DES MOINES WATER WORKS CORROSION …...3 | Page Figure 4: Piece of Pipe Exposed to Multiple Environments Electrolytic corrosion is often referred to as stray current corrosion. The

DES MOINES WATER WORKS

CORROSION CONTROL

PROGRAM REPORT

Prepared by

Katrina Kinsey, Professional Engineer Taylor Andrew, Engineering Technician

June 2016

Table of Contents Topic Page Introduction 1 Anode Retrofit Program 7 Anode Retrofit Program 8 Criteria for Anode Retrofit Program 8 Anode Retrofit Program Installations 8 Pipe-to-Soil Potentials 15 Backfill Material Study 16 Anode Life Expectancy Study 17 Reduced Number of Broken Water Mains 20 City of Des Moines Support 20 Economic Analysis 21 Recommendations 22 Anode Installation During Main Break Repairs 23 Anode Installation During Main Break Repairs 24 Anode Attachment Study 24 Recommendations 25 Corrosion Protection on New Small Ductile Iron Water Mains 26 Corrosion Protection on New Small Ductile Iron Water Mains 27 Recommendations 29 Corrosion Control Systems on Feeder Mains 30 Corrosion Control Systems on Feeder Mains 31 Cathodic Protection on Feeder Mains 32 Corrosion Monitoring on Feeder Mains 33 Recommendations 35 Corrosion of Existing PCCP Feeder Mains 36 Corroded Joints Found in 2010 37 Leaking Joint Found in 2016 38 Recommendations 40 Recommendations 41 Anode Retrofit Program 42 Anode Installation During Main Break Repairs 42 Corrosion Protection on New Small Ductile Iron Water Mains 43 Corrosion Control Systems on Feeder Mains 43 Corrosion of Existing Feeder Mains 43 Appendix 44

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Introduction Water utilities throughout the United States and Canada have been dealing with the deterioration of underground water distribution systems for a number of years. In 2001, AWWA stated in a report called the Dawn of the Replacement Era that water utilities have a significant amount of buried infrastructure that is at or very near the end of its life expectancy. These water mains were installed at different times in history and each of them has a different life expectancy that is coming to an end all at the same time. These distribution systems were primarily constructed using cast iron pipe. Iron is a readily available product and easy to refine into suitable materials used for construction of distribution systems. Some products formed by refining iron include cast iron, ductile iron, and steel, all of which provide high strength and watertight joints. The issue we are facing using iron products is that they are susceptible to corrosion when exposed to environmental elements. Corrosion is accelerating these water mains to reach their life expectancy often quicker than expected, and the need to rehabilitate or replace these water mains has been rising at an increasing rate. A way to extend the life expectancy of these water mains, so to reduce the replacement cost, was examined. The life expectancy of a water main is determined by how deteriorated the water main becomes before it is no longer useable. The deterioration of these water mains is caused by corrosion. Corrosion can be defined as the degradation of a metal to revert back to its original state. Corrosion is a natural process that starts with a metal ore. It is then refined and milled to produce an iron pipe. When that iron pipe is buried and exposed to the environment, corrosion allows the iron pipe to revert to its original stable metal ore as shown below in Figure 1. Corrosion is a chemical reaction between a metal and its environment. Stopping iron corrosion requires the environment to be altered such as removing water and oxygen or by applying an external electrical current to replace electrons leaving the iron during the oxidation of the metal as shown below in Figure 2.

Figure 1: Life Cycle of an Iron Pipe

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Figure 2: Corrosion Process

There are different types of corrosion, but there are only two basic types of corrosion for metallic water mains. These basic types are galvanic and electrolytic corrosion. Both of these types of corrosion have the same four main components that must be in place for corrosion to occur: (1) an anode, (2) a cathode, (3) an electrolyte, and (4) a metallic circuit. An anode is the area where corrosion occurs. A cathode is the area where the metal does not corrode. An electrolyte is the environment where the metal is placed (soil or water). A metallic circuit is an electrical connection between the anode and the cathode. Galvanic corrosion is a natural process where two different (dissimilar) metals are in contact in the same environment as shown in Figure 3 or when one piece of metal is exposed to multiple environments as shown in Figure 4. When dissimilar metals are in contact or when a piece of pipe is exposed to different environments, a current flow is generated creating an anodic area and a cathodic area. Electrons from the anodic area flow to the cathodic area creating an area where there is corrosion (metal loss) at the anodic area. The cathodic area does not lose metal so it is apparent the cathodic area is protected from corrosion.

Figure 3: Dissimilar Metals

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Figure 4: Piece of Pipe Exposed to Multiple Environments

Electrolytic corrosion is often referred to as stray current corrosion. The current that causes electrolytic corrosion is often the result of DC current flow from man-made sources. Some sources include other pipelines, power lines, welding operations, and electroplating. The location where the water main receives the stray current is the cathodic area that does not lose metal. The location where the stray current leaves the water main will cause that location to be anodic and will corrode at an accelerated rate. Des Moines Water Works (DMWW) is a municipally owned water utility that serves more than 500,000 customers in central Iowa and began supplying water in 1871. The DMWW water distribution system consist of 1,428 miles of water mains which includes water main from 2 inches to 60 inches in diameter in various materials including but not limited to cast iron, ductile iron, polyvinyl chloride, steel, and prestressed concrete cylinder pipe. The oldest water main that is still in use in the DMWW distribution system was installed in 1872. Of the 1,428 miles, there are 581 miles of water mains that have reached their life expectancy, and another 63 miles will be reaching their life expectancy during the next ten years. The need for funds to replace the depreciated water mains has increased beyond funding capabilities. Water utilities encounter a number of problems while producing quality water for their customers. One major issue that is problematic to water utilities is water main breaks. Water main breaks are not only disruptive, but they are also costly, dangerous to the community, and affect firefighting capabilities. Damages that can be caused by water main breaks include property damage, public safety, public health, travel delays, loss of time to the public, etc. The resulting repair costs for damages may be a significant factor in the overall operating costs of a water utility. Since 1992, DMWW has seen a steady increase in main breaks as shown in Figure 5. The trendline in this graph shows that by 2030, DMWW will have on average 400 main breaks per year. Visual and metallurgical examination of our water mains indicates that the majority of the water main breaks in our distribution system can be either directly or indirectly related to corrosion. Rarely do we find a main break that corrosion has not contributed to its failure, unless a contractor excavating around our water main has damaged it.

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Figure 5: Total Main Breaks

The majority of the main breaks that DMWW repairs is on cast iron water mains as shown in Figure 6. In 2015, 90 percent of all the main breaks were on cast iron water mains. There are two types of cast iron pipe: pit-cast iron pipe and spin-cast iron pipe. Pit-cast iron pipe was vertically cast into a pit. Using this method the slag would collect at the top of the casting which could easily be removed. The cast iron industry shifted to a different technique of manufacturing cast iron pipe using a spin casting. Spin-cast iron pipe was manufactured using a centrifugal cast. The thickness on the spin-cast iron pipe is significantly thinner than that of pit-cast iron pipe in order to cut down on material and costs due to war times. This thinner wall pipe has less material, so failures from corrosion are more prominent than that of pit-cast iron pipe.

Figure 6: Total Main Breaks by Material

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While the number of main breaks has been rising, the cost to repair main breaks has also been rising each year as shown in Figures 7 and 8. These direct repair costs reflect the actual material costs, labor costs (including benefits with no overheads), and equipment costs.

Year Number of Main Breaks

Equipment Cost

Material Cost

Personnel Cost

Total Cost Repair Cost

per Main Break

2001 310 $111,191 $333,880 $477,644 $922,715 $2,976.50 2002 269 $119,031 $241,533 $430,979 $791,543 $2,942.54 2003 276 $136,613 $383,887 $525,014 $1,045,514 $3,788.09 2004 284 $116,600 $282,098 $464,801 $863,499 $3,040.49 2005 358 $121,582 $406,054 $607,912 $1,135,548 $3,171.92 2006 270 $114,615 $455,383 $573,076 $1,143,075 $4,233.61 2007 327 $145,017 $594,266 $725,085 $1,464,368 $4,478.19 2008 252 $125,152 $468,585 $625,758 $1,219,495 $4,839.27 2009 244 $137,901 $562,861 $689,503 $1,390,264 $5,697.80 2010 247 $130,790 $427,392 $653,951 $1,212,133 $4,907.42 2011 300 $166,544 $612,452 $832,719 $1,611,715 $5,372.38 2012 353 $200,058 $830,517 $1,000,288 $2,030,863 $5,753.15 2013 342 $214,574 $714,499 $1,072,868 $2,001,941 $5,853.63 2014 423 $272,776 $1,591,342 $1,363,882 $3,228,000 $7,631.21 2015 210 $166,605 $643,957 $833,027 $1,643,589 $7,826.62

Figure 7: Direct Main Break Repair Cost

Figure 8: Direct Cost for a Main Break Repair

As shown by the red trendline in Figure 8, DMWW is experiencing the direct repair cost of a main break to increase exponentially each year since 2001. It is estimated based on the red trendline, the direct cost to repair a main break will exceed $10,000 in 2019.

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The direct repair costs were obtained by using the actual costs from the financial records. Obtaining the indirect repair costs can be much more difficult. We utilized the AWWARF Grand Central Model to help us calculate the direct and indirect costs of infrastructure failures. The direct cost component calculated in the Grand Central Model for 2015 was $8,020 and the indirect cost component calculated was $16,466. The direct cost of $8,020 for 2015 from the model compares to DMWW’s direct costs from our financial records of $7,800. With limited resources needed to replace the depreciated iron water mains that have an increasing number of main breaks, DMWW was forced to investigate alternatives to water main replacement. Through this investigation, DMWW determined the most cost effective way of controlling corrosion and extending the life of the water mains was to install anodes on water mains. This alternative lowers the system maintenance and repair costs by reducing the number of main breaks. DMWW implemented the use of galvanic corrosion by installing sacrificial anodes to the distribution system. Galvanic corrosion provides reliable corrosion control, that is easy to maintain, and was the most inexpensive solution to our corrosion problem. Cathodic protection mitigates corrosion by providing an electrical current that causes the water main to become the cathode relative to the expendable anode metal. The anodes are sacrificed to protect the water mains from corrosion (extending the life of the distribution system). The use of sacrificial anodes has expanded from existing infrastructure to installing anodes on new infrastructure. Using this strategy, DMWW has implemented multiple corrosion control programs. DMWW has four components of the current corrosion control program as listed below with plans to implement a fifth plan as indicated later in the report:

Anode Retrofit Program Anode Installation During Main Break Repairs Corrosion Protection on New Small Ductile Iron Water Mains Corrosion Control Systems on Feeder Mains Anode Retrofit Program on Existing Small Ductile Iron Water Mains (new)

This report will provide information on the success of our corrosion control programs with recommendations for their future use. This report will also discuss a study for determining how to control corrosion on existing feeder mains.

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ANODE RETROFIT PROGRAM

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Anode Retrofit Program The anode retrofit program utilizes a cathodic protection system. This program retrofits 32-pound sacrificial anodes to existing cast iron and ductile iron water mains. These anodes are spaced at intervals above the water main based on the size of the water main and are connected to the pipeline utilizing vacuum soil excavating and welding. Test stations are another very important component of the anode retrofit program. These test stations are spaced throughout the project and utilized for obtaining readings that help determine the effectiveness of the program. In the DMWW distribution system, the majority of the water mains are in highly corrosive soils except for a few at the river bottoms where they tend to be far less corrosive. Our corrosion engineer working cooperatively with DMWW’s staff determined the average anode spacing based upon soil resistivity testing on a select group of pipe segments shown in Figure 9:

Pipe Diameter (in.) Anode Spacing (ft.) 6 65 8 50

12 37 Figure 9: Anode Spacing for the Anode Retrofit Program

Criteria for Anode Retrofit Program The water mains selected for each year’s installations were based upon several criteria including pipe size, pipe material, future demands, pipe age, number of main breaks on the pipe, condition of the pipe, the ease of installation of the anodes, soil characteristics, traffic disruption, inconvenience to customers, excavation costs, and restoration costs. For example, installing anodes on existing water mains located in grassy areas behind a curb is less costly than installing anodes on water mains under paving. Installing anodes on water mains under paving requires extra steps that increase the cost, including core drilling and replacing pavement. Future demand is also big factor that should be at the top of the list when deciding whether to select a specific street. If the water main is not adequately sized for the current distribution system or for the future, it should be replaced and is not considered as a candidate for this program. During the first few years of the anode retrofit program, streets with high main break rates were selected for the program to determine if the anode retrofit program would actually reduce main breaks. After DMWW was able to prove that the anode retrofit program worked, DMWW continued to select streets with high break rates. Anode Retrofit Program Installations DMWW has installed the anode retrofit program on existing water mains from 2004 to 2014. In 2015 and 2016, the program was not funded. Over the years we have modified our installation practices with more effective practices as summarized below in Figure 10.

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Task 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Vacuum Excavation X X X X X X X X X X X

Backhoe Excavation X

Core Drilling X X X X X X X X X X Stud Weld Anode to Main

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Clamp Anode to Main X Pin-Brazing Anode to Main

X X X X

Exothermic Weld Anode to Main

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Anodes X X X X X X X X X X X

Test Stations X X X X X X X X X X X

Backfill with Soil X

Backfill with Sand X Backfill with Low-Strength Concrete

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Backfill with Mansand X X

Restoration X X X X X X X X X X X

Figure 10: Anode Retrofit Program Installation Process 2004-2014 In 2004, our pilot program included vacuum excavating a 12-inch-diameter hole, stud welding anodes to the water main, clamping the anode wire to the water main, encasing the anode with sand, and backfilling with soil. We found that stud welding the anodes to existing spin-cast iron water mains worked, but we had problems with stud welding the anodes to existing pit-cast iron water mains. We found utilizing pipe clamps to attach the anodes to existing pit-cast iron water mains worked. When we used pipe clamps, the vacuum excavated hole expanded to a larger backhoe excavated hole which caused the cost to increase for these installations. We also had issues determining how to properly clean the pipe for the stud weld connection. DMWW tested the stud welder to make sure it would work at DMWW prior to taking all the equipment out to the site as shown in Figure 11.

Figure 11: Stud Weld Attachment

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In 2005, some of the streets selected required the anodes to be installed under paving. Core drilling was added as an installation method as shown in Figures 12 and 13. We switched the backfill material from soil to sand because we were trying to eliminate any settlement in the excavated hole. The stud welder worked very well throughout this project since we were attaching to spin-cast iron pipe. We were still figuring out how to more effectively clean the pipe for the stud weld connection.

Figure 12: Core Drilling

Figure 13: Vacuum Excavating the Core Drilled Hole

In 2006, we found a less expensive method of attaching anodes to existing water mains utilizing a pin-brazing technique as shown in Figure 14, but it still did not work well with attaching the anode to pit-cast iron pipe. We also shifted from the installation of sand backfill to low-strength concrete

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backfill to eliminate the settlement in the excavated hole. By the end of installing the anode retrofit program in 2006, DMWW determined sandblasting was the best way to clean the pipe for a stud weld connection.

Figure 14: Pin-Brazing Technique

In 2010, we found a method that would allow for us to install the anode retrofit program on pit-cast iron pipe utilizing an exothermic weld as shown in Figures 15, 16, and 17. We have discovered the exothermic weld will attach the anode to any type of iron pipe. The exothermic welder has been DMWW’s preferred method for attaching the anode wire to the water main.

Figure 15: Crew Welding with the Exothermic Welder

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Figure 16: Exothermic Welder in a Core Drilled Hole

Figure 17: Exothermic Weld

In 2013, we switched the backfill material from low-strength concrete to manufactured sand to speed up the installation process and cut costs. The settlement issues we saw in 2005 have not reappeared since switching the backfill material because DMWW is flooding the vacuum excavated holes with water to eliminate any settling with the manufactured sand. In 2014, no installation methods had changed since the 2013 Anode Retrofit Program. A detail of how to install an anode with a test station in both the parking and under pavement is shown in Figure 18.

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Figure 18: 2014 Anode Retrofit Program Details

Figure 19 summarizes the installations of our anode retrofit program. The table shows the amount of water main that has been protected for each year that the anode retrofit program was installed. Currently, a total of 117,628 feet of existing water main has been cathodically protected with this program which includes 2,321 anodes and 253 test stations.

Year 2004 2005 2006 2007 2008 2009

Water Main Protected (ft.) 2,672 9,935 14,040 9,277 10,384 10,966 # of Anodes Installed 49 221 278 167 212 216

# of Test Stations Installed 6 26 27 31 37 46 Total Cost of Project ($) $24,691.14 $105,179.06 $148,725.51 $132,994.24 $115,748.39 $128,810.68

Cost per Anode ($) $503.90 $475.92 $534.98 $796.37 $545.98 $596.35 Project Cost ($/ft.) $9.24 $10.59 $10.59 $14.34 $11.15 $11.75

Year 2010 2011 2012 2013 2014 Total

Water Main Protected (ft.) 8,299 14,465 13,598 11,752 12,240 117,628 # of Anodes Installed 159 286 255 233 245 2,321

# of Test Stations Installed 34 16 7 11 12 253 Total Cost of Project ($) $112,519.50 $209,894.49 $181,763.92 $183,921.30 $174,531.77 1,518,780.00

Cost per Anode ($) $707.67 $733.90 $712.80 $789.36 $712.37 $654.36 Project Cost ($/ft.) $13.56 $14.51 $13.37 $15.65 $14.26 $12.91

Figure 19: Anode Retrofit Program Installation Summary 2004-2014

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In recent years, test stations have been reduced to one test station per street for the anode retrofit projects since previous testing has proven that anodes reduce corrosion and water main breaks. Shown below in Figures 20 and 21 are the actual cost per anode and the actual total project cost per foot for each year that the anode retrofit program was installed. Also, shown on both graphs is the cost based on the Engineering News Record Construction Cost Index. Both of these graphs show that the actual costs have been increasing at a faster rate than the cost would be based on the Engineering News Record Construction Cost Index since this project began in 2004, mainly due to inflation and the cost of construction.

Figure 20: Cost per Anode for Anode Retrofit Program

Figure 21: Project Cost per Foot for the Anode Retrofit Program

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Pipe-to-Soil Potentials The determination of the effectiveness of the anode retrofit program for water mains requires the measurement of the electrical potential (voltage) of the water main utilizing a standard portable reference electrode that has a constant and reproducible potential. To determine this potential, a special multimeter, as shown in Figure 22, is used to measure the difference in the potential between the water main and the reference electrode which is placed in direct contact with the soil directly over the water main. This measurement is known as a pipe-to-soil potential.

Figure 22: Multimeter

Pipe-to-soil potentials are easily and accurately obtained where existing water mains are in grassy areas behind the curb or in locations that the portable reference electrode can make contact with the soil directly over the water main. However, where existing water mains are located under pavement, the pipe-to-soil potentials are not as easily or accurately obtained because the portable reference electrode is not in contact with the soil directly over the water main. To address this issue of not being able to contact soil above the water main, DMWW has updated the test stations by adding a buried reference electrode to facilitate the measurement of more accurate pipe-to-soil potential data in paved areas. Throughout our project, we have consistently measured the pipe‐to‐soil potential of the water main prior to installing the anodes at locations where the anodes will be installed. This is called the baseline potential profile (pre-test). We obtain these measurements by connecting to the water main utilizing existing valves and hydrants. After the anodes have been installed, a second set of potential readings are measured over and between each anode at the same locations as the pre-test. We obtain these measurements utilizing the anode test stations. This set of potential readings is called the post-installation potential profile (post-test). By comparing the average “shift” in pipe-to-soil potential readings between the two data sets, we can infer the effectiveness of the cathodic protection of the anodes.

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Data from several Canadian water utilities have shown that cathodic protection systems installed on existing cast iron water mains will significantly reduce the rate of corrosion on those systems where 100 millivolts or more pipe‐to‐soil potential shifts are measured after installing the anodes. In 2015, follow-up pipe-to-soil potential measurements were completed on the anode retrofit programs from 2004 to 2014. In only a few instances, the potential shifts less than 100 millivolts as shown in Figure 23 in the pipe-to-soil potential graph. The blue line on the graph is the baseline potential profile and the red line on the graph is the post-installation potential profile. The purple, yellow, and green lines on the graph are follow-up pipe-to-soil potential measurements obtained during different years. The peaks shown on the graph are located at anodes and the valleys are located between the anodes. Keep in mind that the data can be misleading in areas that the main is located under the paving. As previously stated, the portable reference electrode needs to be in contact with the soil above the existing water main for accurate readings.

Figure 23: Pipe-to-Soil Potential Graph

Backfill Material Study In 2016, DMWW completed a backfill material study to determine the most effective backfill material for the anode retrofit program. The backfill material we used in the study was soil, manufactured sand, and low-strength concrete. A buried reference electrode and test station were added at each buried anode location to measure the pipe-to-soil potential. We will continue to monitor this study over time, since currently there is not enough data to make a recommendation.

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For the 2017 Anode Retrofit Program, we will continue to use the same installation methods that were used in the 2014 Anode Retrofit Program and continue to use manufactured sand as the backfill material. Figure 24 shows the installation of the backfill material study where the blue test wire is exothermically welded to the water main, the reference electrode with the yellow wire, and the white anode with a black wire in a vacuum excavated hole. All three wires are brought up into a test station; inside the test station the blue wire and the black wire are hooked together to complete the circuit. The yellow buried reference electrode wire was added to accurately measure the pre-test and post-test pipe-to-soil potentials at each location.

Figure 24: 2016 Backfill Material Study – Backfill Test

Anode Life Expectancy Study In our original report in 2004 and each report after that, we used a 20-year life expectancy for a 32-pound anode based on the recommendation from our corrosion engineer and data that was obtained from anodes in the 2005, 2006, and 2007 anode retrofit installations. In 2015 and 2016, DMWW completed an anode life expectancy study by digging up thirteen anodes from different years of the anode retrofit program to help determine the life expectancy of an anode. DMWW uses a standard 32-pound anode for our anode installations. When a brand new off-the-shelf 32-pound anode was weighed for this study, we found it to weigh 34 pounds. All of these anodes that were dug up were weighed to determine how much of the anode corroded during the time it was protecting the existing water main. Most of the anodes dug up looked like the picture on the left side in Figure 25 and lost approximately 0.3 pounds per year the anode was protecting the existing water main. One of the thirteen did not look like the others when it was dug up as shown in the picture on the right side in Figure 25. After three years of protecting the existing water main, this anode corroded so much that 1 pound of the anode was left when it was dug up. This anode was installed on a water main that was in an area where there was very corrosive soils and a high ground water table. Corrosive soils and a high water table can accelerate

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the rate of decay for the anodes; therefore, dry soil conditions can lead to less current output and less degradation of the anode. As the anode decays its resistance to the soil will increase and lead to less current output.

Figure 25: Anodes Dug Up

All the data gathered from weighing the anodes that were dug up is shown in Figure 26. The graph in Figure 27 is the same graph except the data for the anode that was almost completely corroded is removed. The red trendline shows that as the anodes age the more corroded they become.

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Figure 26: Anode Life Expectancy

Figure 27: Anode Life Expectancy without Anomaly

Figure 28 shows this same graph but with the red trendline extended out to future years. According to this graph, a 32-pound anode will protect an existing water main on average about 25 years.

Figure 28: Expected Anode Service Life

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Previously DMWW has used a 20-year life expectancy for a 32-pound anode. Based on the research completed when the anodes were dug up and weighing them to determine how much of the 32-pound anode has corroded, we will begin using a 25-year life expectancy for evaluation of our installations. Figure 29 represents the anode open-circuit potential for each anode that was part of the anode life expectancy study. The anode open-circuit potential is recorded by unhooking the anode from the water main and utilizing a portable reference electrode. These open-circuit potentials were recorded before the anodes were dug up and removed to record weight loss. The results in Figure 29 reflect that the existing water mains remained protected by the sacrificial anodes and the potentials remain high throughout the degradation of the anode.

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Figure 29: Anode Age versus Anode Open-Circuit Potential versus Weight Loss Reduced Number of Broken Water Mains The anode retrofit program has reduced main breaks on 177,628 feet of water main. Prior to anode retrofit installations, the main breaks were increasing. After the anode retrofit installations, the main breaks started to decrease. Using the trendlines from the main break data of the water mains prior to anode installation, DMWW projects a 5.36 percent per year increase in main breaks. Assuming that the anode retrofit program was not installed and main breaks increased at a rate of 5.36 percent per year, there would be a 60.5 percent reduction in main breaks. City of Des Moines Support The City of Des Moines has a huge investment in their street infrastructure. The majority of the indirect repair cost includes damage to street infrastructure and travel delays. The Engineering and Traffic Departments of the City of Des Moines have had a great interest in our project from

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the very beginning since its intent was to lower the number of main breaks, thus decreasing the damage to their valuable street infrastructure. We have made modifications to the installation process based on their concerns and feedback. With these concerns addressed, the City has continued to be supportive with the results of our installations and the decreased number of main breaks. Economic Analysis All dollars used in the economic analysis have been converted to 2016 costs using the Engineering News Record Construction Cost Index and the interest rate of borrowing money has been excluded from all costs. Based on the direct costs for repairing main breaks in 2015 of $7,826.62, reducing main breaks by at least 60.5 percent, and using an anode life expectancy of 25 years, an analysis could be completed. Figure 30 shows the total life cycle cost for anode retrofit installations, the total life cycle cost for water main replacement, and the total life cycle cost to do nothing including repairing main breaks based over the 25-year life expectancy of the anode retrofit program.

Figure 30: Economic Analysis When Reducing Main Breaks by 60.5 Percent

This graph shows that at the current reduction of main breaks of 60.5 percent, water main replacement is more cost effective than installing an anode retrofit program. DMWW assumes this reduction factor will continue to increase each year as the anode retrofit program continues to minimize main breaks. For the installation of the anode retrofit program to be more cost effective than water main replacement, a 73.7 percent reduction in main breaks would need to be obtained. To increase the

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Cost to do Nothing

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current 60.5 percent reduction factor, water mains with at least a break rate of 0.35 breaks per 100 feet over five years will need to be selected for the anode retrofit program. Recommendations The use of anode retrofit to extend the life of DMWW’s distribution iron water mains has shown to reduce the rate of water main breaks by 60.5 percent and our cathodic protection field data suggest that a 25-year life extension on the water main is a very realistic expectation. The economic analysis shows that installing an anode retrofit program to the existing water mains is more cost effective than doing nothing to these deteriorated water mains and just repairing main breaks. However, the analysis also shows that installing an anode retrofit program is less cost effective than replacing water mains when the interest rate of borrowing money has been excluded from the calculations. It is recommended to replace existing water mains when the opportunity is presented. With the limited resources to replace existing water mains, it is recommended to install the anode retrofit program for existing 8-inch and 12-inch cast iron water mains that have a break rate of at least 0.35 breaks per 100 feet over five years. Water mains that are smaller than 8 inches in diameter are too small for fire protection and may be inadequate for future demands. Water mains that are less than 6 inches in diameter will not be considered for this program. Currently the anode retrofit program installs anodes on existing cast iron water mains. We recommend the development of a similar program for ductile iron water mains in our distribution system that were constructed before polyethylene encasement was installed on ductile iron water mains.

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ANODE INSTALLATION DURING MAIN BREAK REPAIRS

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Anode Installation During Main Break Repairs We began a program in 2005 of adding anodes to existing cast iron and ductile iron water mains during a main break repair. When the main break is caused by a beam break or a hole in the pipe, the main break is repaired with a repair band. The anode is attached to the existing water main immediately adjacent to the repair band with a clamp as shown in Figure 31. When the main break is caused by a split or a large failure that requires replacement of pipe, the main break is repaired using two couplings and a piece of pipe wrapped in polyethylene encasement. The anode is attached to the existing water main with two clamps on either side of the two couplings as shown in the sketch in Figure 32. This allows the anode to protect the existing water main.

Figure 31: Main Break Repair with a Repair Band

Figure 32: Main Break Repair with New Pipe

Anode Attachment Study In 2016, DMWW conducted an anode attachment study to evaluate the effectiveness of installing anodes during main break repairs. This study examined the attachment technique during main break repairs to prevent further corrosion. In order to evaluate this study, DMWW installed six

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anodes with a clamp and six with an exothermic weld at specific distances. A buried reference electrode was added to each location to get accurate pre-test and post-test pipe-to-soil readings. The study showed that clamps do not provide as good of a connection to the existing water main as the exothermic weld. During testing, it was determined that the clamp is not consistently making a good connection to the water main; therefore, the clamp is not sending the current from the anode to the water main as effectively as the exothermic weld connection. After one month of this study, the exothermic weld connection had a 280 millivolt increase over the clamp connection in the pipe-to-soil potential as shown in Figure 33.

Figure 33: Anode Attachment Study

Recommendations It is recommended to continue this program of adding anodes to existing cast iron and ductile iron water mains during main break repairs to slow future corrosion to the water main in that particular area. DMWW believes, based on the study, the clamps are providing some benefit of protecting the existing water mains, but the exothermic weld connection proves to protect the existing water main the best. DMWW will research replacing clamps with handheld exothermic welders. After selecting the exothermic welder best suited for the application, the clamp will quickly get phased out. Another recommendation for this program is to implement installing two anodes during a main break repair that requires installation of ductile iron pipe and couplings, rather than a single anode. Safety is a top priority for DMWW, and repairing main breaks is a dangerous job. DMWW continues to encourage all employees to perform their job in the safest manner possible. Anodes present a safety concern, as they are heavy, so the handling of anodes is our number one concern. To eliminate injuries proper installation training, lifting techniques, and PPE are essential to the continued safety and success of this program.

200

400

600

800

1000

1200

19+84 19+94 20+17 20+57 21+22 22+05

Pip

e-to

-Soi

l Pot

enti

als

Weld Connection versus Clamp Connection

Baseline

Apr-16 Clamp

Apr-16 Weld

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CORROSION PROTECTION ON NEW SMALL DUCTILE IRON

WATER MAINS

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Corrosion Protection on New Small Ductile Iron Water Mains A program was started in 2010 to add cathodic protection to the new small diameter (8-inch to 16-inch) ductile iron water mains. The idea for the small main cathodic protection program was to include this work while the contractor was installing a new ductile iron water main as shown in Figure 34.

Figure 34: Installation of Corrosion Protection on New Small Ductile Iron Water Mains

This work includes anodes spaced at specified intervals along the water main, bonding cables across the pipe joints, an isolation coupling to discontinue the continuity between the existing iron water main and the new ductile iron water main, insulated corporation stops for water services, and test stations. Based on the soil potentials that have been found around the Des Moines metro area, the spacing intervals for the anodes was determined as shown in Figure 35. The anode spacing for the cathodic protection on new small ductile iron water mains is further apart than the anode spacing for the anode retrofit project, because the new small ductile iron water mains have an additional layer of protection from corrosion with the polyethylene encasement compared to the bare iron water mains that the anode retrofit program is installed on.

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Pipe Diameter (in.) Anode O-C Spacing (ft.) 8 90

10 72 12 60 16 45

Figure 35: Anode Spacing for Cathodic Protection on New Small Ductile Iron Water Mains Program Starting in 2014, a buried reference electrode was added to each test station so that it could be tested. Figure 36 summarizes the water mains that have the testing capability. The cathodic protection on these testable water mains was first tested in 2016. Currently there is not enough data to confirm how well the anodes are protecting the water mains from corroding, but the system does appear to be working between the cathodic protection and the polyethylene encasement around the water main. DMWW feels confident that this program will prove to work because the anode retrofit program is similar to this program.

Water Main Information File Information

Street From To Length Install Date Testable Not Testable Mulberry 13th 15th 930 6/1/2011 x

Hubbell University Searle 850 6/9/2011 x

2nd Ave Walnut Court 550 7/21/2011 x

Emma SW 9th SW 8th 200 9/8/2011 x

SE 14th Watrous 200' South 190 10/5/2011 x

SE 1st Court 200' South 200 8/10/2012 x

McKinley Fleur SW 19th 680 10/15/2012 x

Army Post SE 5th 300' East 270 11/1/2012 x

Army Post SE 14th 700' West 670 11/1/2012 x

Payton Ave Fleur 200' East 200 11/14/2013 x

SE Connector SE 15th SE 18th 1990 10/7/2013 x

SE 18th Scott Market 1150 10/7/2013 x

Market SW 4th SW 5th 350 11/15/2014 x

Wakonda View Fleur 400' West 435 10/30/2014 x

SW 9th Hackley Titus 440 5/8/2015 x

Figure 36: Cathodic Protection on New Small Ductile Iron Water Mains Program Installation Summary The cost for adding cathodic protection to new small ductile iron water mains is approximately 3 percent of the total project cost. This cathodic protection system is designed to protect the water main where it comes in contact with the soil. If the water main did not have a polyethylene encasement, the life expectancy of the water main in our corrosive soils would be approximately 50 years. With the polyethylene encasement around the water main, it extends the life expectancy to 75 years. With the added cathodic protection to the ductile iron polyethylene encased water main, the life expectancy is extended to 100 years. The small added cost for cathodic protection significantly increases the life expectancy for all new small ductile iron water mains.

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A detail of how the cathodic protection system is installed on the new small ductile iron water mains is shown in Figure 37.

Figure 37: Cathodic Protection on New Small Ductile Iron Water Mains Program Details

Recommendations It is recommended that we continue this program of adding cathodic protection to new small ductile iron water mains. By adding a 3 percent increase in cost to the projects for this program, the life expectancy of the water mains has doubled. The cathodic protection on these water mains will be tested every two years to look for any corrosion on the water mains.

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CORROSION CONTROL SYSTEMS ON FEEDER MAINS

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Corrosion Control Systems on Feeder Mains Protecting and extending the life of feeder mains (16-inch and larger) is very important for the DMWW distribution system. DMWW has installed two different types of corrosion control for water mains that are 16-inch diameter. In one instance, a 16-inch water main was installed with a New Small Ductile Iron Water Mains Cathodic Protection Program; and in another instance, a 16-inch water main was installed with a Corrosion Control System for Feeder Mains Program. For DMWW, a 16-inch water main could be designed with a small main or a feeder main corrosion system. This determination is based on the soils around the water main. If the soils are sandy, the corrosion control system for the 16-inch water main will be designed under the New Small Ductile Iron Water Mains Cathodic Program. If the soils are anything but sandy, the corrosion control system for the 16-inch water main will be designed as a feeder main by our corrosion engineer. DMWW’s feeder mains provide large quantities of water that travel from our treatment plants to our customers. Failures on feeder mains can be a catastrophic to any distribution system. When one of these feeder mains has a failure, it could be isolated and shut down for a long period of time in order to get all the parts needed to repair the failure, since these parts are not necessarily readily available and very costly. DMWW chose to install corrosion control systems on new feeder mains to help protect and extend the life of these feeder mains. Two types of corrosion control that were installed are cathodic protection and corrosion monitoring. Currently, DMWW is cathodically protecting or has a corrosion monitoring system on 29.4 miles of feeder mains within the distribution system. Figure 38 shows the number of miles that are currently cathodically protected or has a corrosion monitoring system. Figure 39 shows the number of miles per material that DMWW has installed in a corrosion control system.

Figure 38: Miles of Corrosion Control Systems

Cathodic Protection

Corrosion Monitoring

10.1

19.3

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Figure 39: Miles per Material with Corrosion Control Systems

An Operating and Maintenance Manual was prepared by DMWW engineering staff and our corrosion engineer for the cathodic protection and corrosion monitoring systems that have been installed on new feeder mains in the DMWW distribution system. Sections of the Operating and Maintenance Manual is included in the Appendix with sample drawings and inspection forms. Cathodic Protection on Feeder Mains A program was started in 2003 to install cathodic protection on newly installed ductile iron and welded steel pipe. This system would be installed while the contractor was installing the new feeder main. This work includes bonding cables across the pipe joints, flange isolations kits as shown below in Figure 40, anode fields spaced at specified intervals along the feeder main as shown below in Figure 41, reference electrodes, and test stations. Each contract that uses this program is designed by our corrosion engineer and is unique to other contracts. The cost for adding cathodic protection to a feeder main contract is approximately 4.5 percent of the total project cost.

Figure 40: Flange Isolation Kit for Cathodic Protection on Feeder Mains

Ductile Iron Pipe

PrestressedConcrete CylinderPipe

Welded Steel Pipe

9.9

18.6

0.9

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Figure 41: Anode Installation for Cathodic Protection on Feeder Mains

Maintenance of these systems includes inspections every two years. During these inspections, a visual inspection of the test station is completed and readings are obtained and graphed. The inspections and readings are used to determine the effectiveness of the cathodic protection system and to determine if any repairs are required. An example of the readings that are obtained during an inspection can be viewed in the Operating and Maintenance Manual that is included in the Appendix. Corrosion Monitoring on Feeder Mains A program was started in 1997 to begin corrosion monitoring on newly installed prestressed concrete cylinder pipe (PCCP) in the distribution system. This system would be installed while

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the contractor was installing the new feeder main. Corrosion potentials are monitored through test stations that are placed along the feeder main. These test stations have wires attached to the feeder main, bonding cables across the joints to make the feeder main electrically continuous, and a reference electrode buried next to the feeder main. There are no sacrificial anodes installed for any PCCP feeder mains. Each test station allows DMWW to obtain the potential through the soil to measure locations for corrosion. Figure 42 shows the bonding cables getting welded to the PCCP at each joint. Each contract that uses this program is designed by our corrosion engineer and is unique to other contracts.

Figure 42: Bonding Cables Welded to PCCP Joints

Corrosion monitoring inspections are scheduled to be completed every four years on PCCP. These inspections are to be completed during the summer of 2016 and then every four years after that. Figure 43 shows an example of the readings that are obtained during an inspection for corrosion monitoring.

Test Station Info. DMWW Water

Main Foreign Structure

Latest Survey Remarks Approx. P/L STA

#

TS Type

ON P/S I-O P/S

(-mV CSE)

(-mV CSE)

(-mV CSE)

1001+40 ITS #N/A #N/A FIK at N. Collector Well

1004+06 PTS 551 Near N. Collector Well

1013+43 PTS 594 Near Pipe 90 Degree

1022+25 PTS 587

1031+38 PTS 605

1035+51 ITS #N/A #N/A FIK at GV N. of Tee Figure 43: Example of Readings Obtained During Inspections

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Recommendations It is recommended for the cathodic protection program for the feeder mains, to continue to inspect these test stations every two years and to obtain readings that are necessary to determine the effectiveness of the cathodic protection system. Using the visual inspections and the data from the readings that have been obtained, repairs have been completed to ensure that the anode fields are working properly. It is recommended for the corrosion monitoring program for the feeder mains, for the inspections to remain scheduled every four years. Using these readings that are obtained during the inspections can help determine if there are any anomalies that would show if corrosion is taking place.

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CORROSION OF EXISTING PCCP FEEDER MAINS

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Corroded Joints Found in 2010 In 2010, DMWW was involved with a project to relocate a 30-inch PCCP feeder main that was installed in 2000 with a 30-inch ductile iron pipe. When making the two connections at both ends of the 30-inch ductile iron feeder main to the 30-inch PCCP, it was discovered that the PCCP joints were corroded as shown in Figures 44, 45, and 46. DMWW was alarmed of this discovery considering the age of the feeder main and the potential disaster this feeder main would cause if there was a failure, both physically to the surrounding areas and for providing water to DMWW customers.

Figure 44: Corroded Joint on PCCP Found in 2010


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Leaking Joint Found in 2016 Early in 2016, a leak was found on a 36-inch PCCP feeder main that was installed in 1997. After the leak was dug up, it was discovered the leak was coming from a joint. The corrosion found on this joint was similar to what was found in 2010 on the other PCCP joints. When this joint was exposed, a portion of the concrete bell and spigot fell off exposing the steel prestressing wires, and corrosion on the joint could be seen as shown in Figures 47 and 48.

Figure 47: Leak Found on PCCP in 2016

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Figure 48: Leak Found on PCCP in 2016

DMWW exposed the pipe joints on either side of the corroded pipe joint and found little to no corrosion on those joints. To repair the corroded joint, two pipes were removed and replaced with new PCCP and a closure piece as shown in Figure 49.

Figure 49: Repair of Leaking PCCP Joint

DMWW believes that improper diaper installations occurred during installation of the PCCP mains. The improper diaper installation created areas in which corrosion was accelerated in the

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steel of the bell and spigot causing the leak. Then corrosion migrated onto the prestressing wires causing the pipe to fall apart during excavation. Since we have seen issues with corroded joints now on two separate PCCP feeder mains, DMWW plans to complete a study to find out why this is happening to the PCCP joints and to determine if this is happening to any other PCCP joints in the distribution system. Recommendations It is recommended that a study will need to be completed to determine if any of the PCCP feeder mains (not just the ones that have corrosion monitoring but all of them) have any leaks, broken prestressing wires, or corrosion occurring. This will help DMWW find locations where failures due to corrosion are likely and prevent them from becoming costly failures.

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RECOMMENDATIONS

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Anode Retrofit Program The use of anode retrofit to extend the life of DMWW’s distribution iron water mains has shown to reduce the rate of water main breaks by 60.5 percent and our cathodic protection field data suggest that a 25-year life extension on the water main is a very realistic expectation. The economic analysis shows that installing an anode retrofit program to the existing water mains is more cost effective than doing nothing to these deteriorated water mains and just repairing main breaks. However, the analysis also shows that installing an anode retrofit program is less cost effective than replacing water mains when the interest rate of borrowing money has been excluded from the calculations. It is recommended to replace existing water mains when the opportunity is presented. With the limited resources to replace existing water mains, it is recommended to install the anode retrofit program for existing 8-inch and 12-inch cast iron water mains that have a break rate of at least 0.35 breaks per 100 feet over five years. Water mains that are smaller than 8 inches in diameter are too small for fire protection and may be inadequate for future demands. Water mains that are less than 6 inches in diameter will not be considered for this program. Currently the anode retrofit program installs anodes on existing cast iron water mains. We recommend the development of a similar program for ductile iron water mains in our distribution system that were constructed before polyethylene encasement was installed on ductile iron water mains. Anode Installation During Main Break Repairs It is recommended to continue this program of adding anodes to existing cast iron and ductile iron water mains during main break repairs to slow future corrosion to the water main in that particular area. DMWW believes, based on the study, the clamps are providing some benefit of protecting the existing water mains, but the exothermic weld connection proves to protect the existing water main the best. DMWW will research replacing clamps with handheld exothermic welders. After selecting the exothermic welder best suited for the application, the clamp will quickly get phased out. Another recommendation for this program is to implement installing two anodes during a main break repair that requires installation of ductile iron pipe and couplings, rather than a single anode. Safety is a top priority for DMWW, and repairing main breaks is a dangerous job. DMWW continues to encourage all employees to perform their job in the safest manner possible. Anodes present a safety concern, as they are heavy, so the handling of anodes is our number one concern. To eliminate injuries proper installation training, lifting techniques, and PPE are essential to the continued safety and success of this program.

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Cathodic Protection on New Small Ductile Iron Water Mains It is recommended that we continue this program of adding cathodic protection to new small ductile iron water mains. By adding a 3 percent increase in cost to the projects for this program, the life expectancy of the water mains has doubled. The cathodic protection on these water mains will be tested every two years to look for any corrosion on the water mains. Corrosion Control Systems on Feeder Mains It is recommended for the cathodic protection program for the feeder mains, to continue to inspect these test stations every two years and to obtain readings that are necessary to determine the effectiveness of the cathodic protection system. Using the visual inspections and the data from the readings that have been obtained, repairs have been completed to ensure that the anode fields are working properly. It is recommended for the corrosion monitoring program for the feeder mains, for the inspections to remain scheduled every four years. Using these readings that are obtained during the inspections can help determine if there are any anomalies that would show if corrosion is taking place. Corrosion of Existing PCCP Feeder Mains It is recommended that a study will need to be completed to determine if any of the PCCP feeder mains (not just the ones that have corrosion monitoring but all of them) have any leaks, broken prestressing wires, or corrosion occurring. This will help DMWW find locations where failures due to corrosion are likely and prevent them from becoming costly failures.

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APPENDIX

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Appendix Description Page Standard Cathodic Protection Corrosion Monitoring/Cathodic Protection Operating & Maintenance Procedures – Water Transmission Feeder Mains 46

STANDARD CATHODIC PROTECTION CORROSION MONITORING/CATHODI PROTECTION C

ATING & MAINTENANCE PROCEDUWATER TRANSMISSION FEEDER MAINS

OPER RES

DES MOINES WATER WORKS ENGINEERING DEPARTMENT

PREPARED BY

____________________________________________________________________________ JEFF SCHRAMUK – NACE CATHODIC PROTECTION SPECIALIST #7695

CP Solutions, Inc. P: 630-235-1559 1167 Independence Drive Page 2 F: 630-289-5964 Bartlett, IL 60103 www.cpsolutionsinc.net

Introduction

History of Pipe Materials Used by Municipal Water Utilities

In the early 20th century, it was common practice for most municipal water utilities (MWU) to

merely bury their water infrastructure with little regard for corrosion. In those days, pipe

materials were robust and corrosion failures on such thick‐walled, pit‐cast iron pipes were

unlikely. In 1920, the process of casting iron water pipes in spinning sand molds was

introduced. Although the spin‐casting process yielded a lighter‐weight pipe material with less

casting imperfections, the thinner pipe walls resulted in higher corrosion failure rates than

the earlier pit‐cast iron pipe. Up until World War II, poured lead pipe joints were common, but

due to the need for lead to serve the war effort, a plasticized sulfur cement known as leadite

was used as a substitute joint sealant. Unfortunately, leadite was found to cause pipe joint

failures by increasing the internal stresses on the pipe and in 1956 improvements in pipe

manufacturing lead to the development of push‐on pipe joints that used rubber gaskets. The

introduction of ductile iron pipe in the mid 1950’s was revolutionary in that it used nodular

graphite which made it stronger than the older gray cast iron alloy. Throughout the period

from the late 1950’s into the 1970’s, MWUs installed many miles of new water mains to serve

suburban population growth that resulted from the post‐war “baby boom.” However, the pipe

materials that were installed during this period are now showing signs that they may not be

as corrosion resistant as was originally estimated. Thus, MWUs may now be at the point

where they face the “perfect storm” of having installed many different pipe materials over the

ast nearly 100 years ‐ each with its own unique limitations due to corrosion failures. l

The Present Water Infrastructure Problem

In 2004, the American Water Works Association (AWWA) began tracking the critical issues

that face MWUs. At that time, regulatory issues and security concerns were the primary issues

facing most MWUs – presumably the result of the 9/11 terrorist attacks of 2001. Fast forward

to 2009 and the AWWA reports that aging water infrastructure is now the most inadequately

addressed issue currently facing MWUs in the United States. Water infrastructure and the

difficulties associated with funding its rehabilitation rank first as a short‐ (one to three years)


and a long‐term (three to five years) concern as well as the issue being most inadequately

ddressed by MWUs. a

Using Cathodic Protection to Control Corrosion

It is now much more important to consider corrosion control for municipal water

infrastructure than it had been in earlier years. For MWU, there are two choices for corrosion

con oltr on buried metallic water infrastructure piping:

1. Install and maintain cathodic protection (CP) systems, or 2. Periodically replace the infrastructure when the leak failure rate becomes an

operational or financial burden.

Properly designed, installed, operated, and maintained CP systems dramatically reduce the

life‐cycle costs by extending a MWU’s infrastructure service life. Reduced water losses due to

corrosion failures, diminished public liability from premature failures, and improved

customer satisfaction are also ancillary benefits of a MWU’s corrosion‐control program.

Industries studies have shown that that corrosion control costs using CP have a life‐cycle ratio

of at least 10 times and often several times more if implemented in the design phase of a

roject. p

Background of the DMWW Corrosion Mitigation Program

The Des Moines Water Works (DMWW) has been more aggressive than many MWU in funding

capital replacement programs. The DMWW has established a portion of its annual budget just

for this purpose based upon the replacement cost for all assets. However, during recent years,

capital funding to allow the replacement of water distribution assets has been redirected to

ater system alterations or DOT projects. w

Both visual and metallurgical examinations indicate that most of the water main breaks in the

DMWW distribution system can be either directly or indirectly related to corrosion. Rarely is a

water main break found that corrosion has not contributed to its failure, unless a contractor

excavating around the pipe has damaged it. With 521 miles of its 1,380‐mile water

distribution system having reached its life expectancy, and another 92 miles reaching its life


expectancy during the next ten years, the DMWW must budget aggressively for water main

replacements. At end of 2007, approximately 36% of DMWW’s distribution system had been

fully depreciated ‐ but not replaced. If these assets were reaching life expectancy at a uniform

rate, the DMWW would need to expend over $2.3M per year on water main replacement.

Thus, CP can be an important component to maintaining the integrity of the DMWW’s existing

water infrastructure or extending the life of its newly‐installed water infrastructure.

Cathodic Protection Theory

Basic Definitions

Although there are numerous forms of metallic corrosion, there are two basic mechanisms for

corrosion of metallic structures. These mechanisms are known as galvanic and electrolytic

corrosion. In either mechanism, the corrosion cell consists of four main components that must

be in place for corrosion to occur:

Anode – Area where corrosion (metal loss) occurs. Cathode – Area where metal does not corrode (metal is protected). . Electrolyte – Environment into which the metal is placed (soil, water, concrete) Metallic Circuit – An electrical connection between the anode and the cathode.

Galvanic Corrosion

Galvanic corrosion is a natural process that results from the differences in electrical potential

energy along a surface of a metal. These electrical potential differences can be caused by the

coupling of dissimilar metals (bi‐metallic corrosion). Non‐homogeneity in the metallurgy of

the structure or variations in the electrolyte (concentration cells) that exist along a metal’s

surface can also cause galvanic corrosion. The process occurs when two dissimilar metals are

electrically connected and are contained within a conductive electrolyte. One of the metals

(the anode) will corrode, and will provide a source of DC current to the other non‐corroding

metal (the cathode). The current flow is from the anode into the conductive electrolyte and

onto the cathode. The anode‐cathode metallic connection completes the circuit and allows the

orrosion reaction to proceed. c


Electrolytic orrosionC

Electrolytic corrosion, which is sometimes called stray current corrosion, is caused by DC

current flow on a metallic structure. The current is often the result of man‐made DC ground

voltages that result from foreign sources such as DC‐powered transit systems, high voltage DC

power transmission lines, electroplating processes, and welding operations. If a metallic

structure intersects these DC ground voltage gradients, differing energy levels will be

introduced along the structure. Where DC current is picked up on the structure from the

surrounding electrolyte, the structure will receive a degree of cathodic protection, if the

current is not too high to degrade the metallurgy of the metal. However, where DC current is

discharged from the metal into the electrolyte, the structure will corrode and metal loss will

occur. The degree of corrosion damage is directly proportional to the magnitude of current

flow from the structure.

Corrosion Mitigation by Cathodic Protection

Cathodic protection is an electrochemical means of corrosion mitigation that minimizes the

anodic dissolution of a metallic structure by reducing the electrical potential energy difference

between the anodic and cathodic sites on a metal’s surface when placed into a conductive

electrolyte. Theoretically, cathodic protection is achieved when the open circuit potentials of

the cathodic sites are polarized to the open circuit potentials of the anodic sites. The goal is to

make the entire structure a cathode (current receiver) relative to an expendable or

replaceable anode (current provider). Specific criteria have been established by the NACE

International for various metals in different electrolytes. The corrosion engineer must

carefully consider these criteria when deciding on the level of cathodic protection to apply to

a metallic structure.

There are two basic methods of applying cathodic protection, although there are many

variations on installing cathodic protection. These two methods are known as sacrificial

galvanic) anodes and impressed current (rectifier) cathodic protection. (

Sacrificial anodes for underground service are usually made of different alloys of magnesium

or zinc. Each type of sacrificial anode will provide a source of cathodic protection current due


to the anode’s higher electrical potential energy than the structure intended for protection.

The Practical Galvanic Series provides guidance on the selection of anodes that can be used to

provide cathodic protection for various metals. The selection of an alloy for a sacrificial anode

must be made with consideration for the electrolyte in which the anode and the structure are

placed. Additional factors are the size and shape of the anode, the structure’s coating, and the

tended design life of the system. in

An impressed current cathodic protection system uses inert anodes that are powered by an

external source of DC current. Anodes can be materials such as graphite, cast iron, and mixed‐

metal oxide‐coated titanium. Many sizes and shapes of impressed current anodes are available

including wire, rods, tubes, sticks, plates, and disks. The composition of the electrolyte is very

important when selecting an impressed current anode. The DC current source is usually a

rectifier, and in this type of system, the anodes are installed within the structure’s electrolyte.

The anodes are connected to the positive output terminal of the rectifier while the structure is

connected to the rectifier’s negative output terminal. Current flow is from the anodes through

the electrolyte and onto the structure. The metallic connection from the structure to the

rectifier completes the DC circuit. Impressed current systems can have many anode

configurations such as deep anode column, shallow anode column, and surface distributed

anode groundbed. The corrosion engineer’s choice of these configurations is dependent upon

he electrolyte and the geometric layout structure to be protected. t

Corrosion Potential Monitoring vs. Cathodic Protection Maintenance For MWUs, metallic water transmission and distribution pipelines are constructed primarily

of gray cast iron, ductile cast iron, carbon steel, or steel embedded in a concrete jacket.

Corrosion monitoring on these types of ferrous pipelines shall refer to the periodic measuring

and recording of pipe‐to‐soil (P/S) corrosion potentials on pipelines installed without CP

systems. For these structures, analysis of P/S potential data can alert the Owner of the more

actively corroding areas relative to the less corroding areas along a buried pipeline. However,

these data must be carefully evaluated by experienced corrosion personnel considering the

following factors:


Materials used to construct the pipeline Age of the pipeline and the presence of corrosion products on the pipe surface pPresence and efficiency of a bonded dielectric coating applied to the ipeline he pipeline that could shield the Any material or foreign structure in the vicinity of tmeasurement of valid P/S data at the pipe surface

Electrical continuity through mechanical pipeline joints Electrical isolation of the pipeline from non‐ferrous metals Characteristics of the soil in which the pipeline is buried Presence of DC ground voltages in the soil in which the pipeline is buried

On ferrous pipelines installed with any type of CP system, regular maintenance shall refer to

the measuring and recording of CP operating data, whether impressed current (rectified)

anodes or passive sacrificial (galvanic) anodes are used. The Owner is responsible for perform

operational checks of the test stations, electrical isolation devices, and all anode systems to

ensure that the long‐term effectiveness of the CP system continues unabated over its intended

design life.

Recommended Schedule: Periodic SpotChecks/Corrosion Monitoring/CP Maintenance

Perform Periodic Spot Checks at least 3‐months prior to any data collection to include: e. o Include the test station hardware and any exposed wire and cabl

o Perform a visual examination of each system component and note any deterioration. o Repair or replace any defective wire or test station components.

Perform a corrosion monitoring survey on water mains installed with electrically continuous pipe and test stations but without CP anodes for either prestressed concrete

nder pipe (PCCP) and welded steel pipe (WSP) to include: o Measure and record P/S corrosion potentials at a spacing of one meter along the entire cyli

length of the buried pipeline using the Close‐Interval Potential Survey (CIPS) technique at least once every 3 years but not greater than once every 5 years.

o Corrosion potential data should be reviewed by a NACE CP Specialist or Professional Engineer.

Perform maintenance inspections on mains installed with CP at intervals not to exceed eve tcom

ry 2 years for WSP and from 1 to 2 years (depending upon the resul s of the initial missioning survey) for poly‐wrapped ductile iron pipe (DIP). Inspections shall include:

o epresentative Measure and record P/S potentials at each test station and other r

o locations along the pipeline.

o Determine the effectiveness of each accessible electrical isolation device. Tabulation/analysis of the data using standard data sheets.

o Cathodic protection data should be reviewed by a NACE CP Specialist or Professional Engineer.

CP Solutions, Inc. P: 630-235-1559 1167 Independence Drive F: 630-289-5964 Bartlett, IL 60103 www.cpsolutionsinc.net

Appendix B – Details of DMWW’s CP/CM Systems

2005-P17.2

Date of Inspection Performed By

ON P/S IO P/S (mV CSE) (mV CSE) (mV CSE) (mA) (mV CSE)

207+50 N/A ITS N/A N/A Water Tower Feed (TS Lost)203+75 TS0000064 ATS 1561 1495 320202+00 N/A ITS 1458 1453 WDM Connection (FIK Bad?)1+82 TS0000062 CTS 1480 7574+00 N/A ATS 1549 1505 209+00 TS0000059 ATS 1529 1495 3011+61 N/A ITS N/A N/A Waukee Connection (TS Lost)13+60 TS0000052 ATS 1558 1509 40102+60 TS0000046 ATS 1540 1480 60 #12 blue lead is bad108+50 TS0000042 ATS 1526 1415 30109+30 TS0000040 CTS 1489 764113+70 TS0000035 ATS 1532 1491 40116+10 AN0000011 CTS 1495 720119+20 TS0000002 ATS 1542 1516 20124+80 TS0000001 ATS 1512 1462 50127+25 AN0000012 CTS 1559 722 #12 blue lead is bad127+76 AN0000013 ITS 1555 531 Connection to existing WTM

Notes:1. All P/S data recorded at discrete test stations using buried CuCuSO4 reference electrode UNO2. Test Leads: Blue (BL) to New WM UNO; White (WH) to Casings/Existing Mains UNO

Date of Inspection Performed By

West Des Moines (University Ave.) Feeder Main [CSPI Ref. 2005P17.2]Test Station Info DMWW Water Main Foreign Anode Anode

2005Jeff Schramuk

7/25/2011Carolanne Norris

West Des Moines (University Ave.) Feeder Main [CSPI Ref. 2005P17.2]Test Station Info. DMWW Water Main Foreign

StructureAnode Current Approx.

P/L STA #TS Type

Anode Output Latest Survey RemarksGIS Com

ID#

ON P/S IO P/S (mV CSE) (mV CSE) (mV CSE) (mA) (mV CSE)

207+50 N/A ITS 936 562 wires reversed203+75 TS0000064 ATS 1057 893 230 1799202+00 N/A ITS 918 8551+82 TS0000062 CTS 919 6664+00 N/A ATS 1040 899 90 18019+00 TS0000059 ATS 922 799 150 165611+61 N/A ITS 920 497 wires reversed13+60 TS0000052 ATS 982 953 200 1660 Reference cell bad 102+60 TS0000046 ATS 1048 827 220 1742108+50 TS0000042 ATS 1012 894 100 1768109+30 TS0000040 CTS 758 438113+70 TS0000035 ATS 823 711 120 1583116+10 AN0000011 CTS 878 675119+20 TS0000002 ATS 937 888 40 1636 black water main wire was not connected124+80 TS0000001 ATS 995 856 160 1758 need cap127+25 AN0000012 CTS 818 546127+76 AN0000013 ITS 868 501

Test Station Info. DMWW Water Main Foreign Structure

Anode Current Approx.

P/L STA #TS Type

GIS Com ID#

Anode Output Latest Survey Remarks

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p

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p

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150

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276

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16

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p

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144’

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14

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00

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LO

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22

LO

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LO

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LO

T 2

25

LO

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26

LO

T 2

27

LO

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28

LO

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31

97th

CO

UR

T (

FU

TU

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AVE.

(FUTURE)

FIL

E N

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BE

R

SH

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T

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LF

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CA

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25’ PERMANENT

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2004 U

NIV

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SIT

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NU

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WD

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FE

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MA

IN

98th

ST

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70 98th

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78 98th

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EA

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OF

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281

28

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19

31

92

191

190

189

188

182

181

180

179

178

17

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174

173

283

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4

285

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OR

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AS

TIN

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AM

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168 581880.9

32 1546526.8

85 1

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62 pip

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168 t

op a

t bell

169 581924.5

7 1546527.4

84 1

045.4

16 pip

e #

169 t

op a

t bell

170 581969.6

47 1546527.4

11 1

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03 pip

e #

170 t

op a

t bell

171 581989.6

61 1546527.3

57 1

044.2

83 pip

e #

171 t

op a

t bell

172 582011.1

93 1546527.7

64 1

043.6

19 pip

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172 t

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t bell

173 582033.9

07 1546527.7

86 1

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89 pip

e #

173 t

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t bell

174 582055.0

59 1546527.9

38 1

041.0

49 pip

e #

174 t

op a

t bell

176 582097.8

29 1546528.4

92 1

039.1

71 pip

e #

176 t

op a

t bell

177 582119.8

28 1546528.8

96 1

038.9

08 pip

e #

177 t

op a

t bell

178 582141.4

65 1546528.9

92 1

038.7

68 pip

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178 t

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t bell

17

9

58

21

63

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15

46

52

9.3

34

10

38

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9

p

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17

9 t

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180 582184.9

66 1546529.4

39 1

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7 pip

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180 t

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181 582206.5

84 1546529.7

32 1

039.4

59 pip

e #

181 t

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t bell

182 582228.3

66 1546529.7

32 1

039.4

34 pip

e #

182 t

op a

t bell

188 582358.2

64 1546530.8

9 1

038.2

65 pip

e #

188 t

op a

t bell

189 582380.4

32 1546531.1

23 1

037.9

74 pip

e #

189 t

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t bell

19

0

58

24

01

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9

15

46

53

1.4

6

10

38

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1

p

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191 582423.1

74 1546531.1

14 1

037.8

12 pip

e #

191 t

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t bell

192 582445.0

48 1546531.7

32 1

037.6

59 pip

e #

192 t

op a

t bell

193 582466.0

44 1546531.8

83 1

037.4

65 pip

e #

193 t

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t bell

256 581872.2

47 1546526.8

09 1

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86 42" c

asin

g

28

1

58

24

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4

15

46

53

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10

35

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7

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286 582467.6

38 1546535.5

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65 te

sts

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287 581978.4

1 1546526.0

96 1

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9 te

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288 581758.6

49 1546526.4

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92 te

sts

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256

168

169

170

17

1172

A

AA

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A

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00

2+

00

3+

00

4+

00

5+

00

6+

00

7+

00

8+

00

9+

00

R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.TELETELETELETELETELETELETELE

98

th S

TR

EE

T

R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.TELETELETELExxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

66’

FE

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100’

100’

25’ PERMANENT

EASEMENT

25’ TEMPORARY

EASEMENT

ELEC

200+00

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25’ TEMPORARY

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FU

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PCPC

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TS

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R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

BISHOP DRIVE(FUTURE)

LO

T 2

28

LO

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29

LO

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30

97th

CO

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T (

FU

TU

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FIL

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BE

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0

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2004 U

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SIT

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WD

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98

th S

TR

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TS

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00

ST

A.

11

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3

24" G

AT

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AL

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11

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3

24

" G

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AL

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GR

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B

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ST

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P.I

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ST

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P.I

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98

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TR

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P.I

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NIV

ER

SIT

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FIN

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6’

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LA

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11

97

198

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289

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202

203

204

257

122

123

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135

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291

A

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29

22

93

AA 2

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A

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INT

N

OR

TH

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E

AS

TIN

G E

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V N

AM

E

PO

INT

N

OR

TH

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E

AS

TIN

G E

LE

V N

AM

E

201 582650.4

55 1546534.1

78 1

035.9

27 pip

e #

201 t

op a

t bell

202 582662.3

01 1546534.2

14 1

035.8

87 pip

e #

202 t

op a

t bell

203 582704.4

14 1546534.3

4 1

035.7

09 pip

e #

203 t

op a

t bell

204 582734.5

64 1546534.7

4 1

035.9

81 pip

e #

204 t

op a

t bell

25

7

58

27

37

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4

15

46

53

2.3

04

10

35

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1

1

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lan

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25

9

58

28

20

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1

15

46

53

5.8

61

10

37

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4

2

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ep

air

28

9

58

24

88

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10

35

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7

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od

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29

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29

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3

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29

1

58

29

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6

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58

29

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3

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53

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10

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122 5

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19 1546546.7

14 1

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77 pip

e #

122 t

op a

t bell

123 5

83190.3

66 1546537.9

89 1

042.3

06 pip

e #

123 t

op a

t bell

12

6

58

30

58

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7

15

46

53

7.1

93

10

40

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7

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15

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1 1546537.4

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12

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29

71

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3

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53

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55

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4

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29

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13

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194 5

82488.0

43 1546532.0

13 1

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39 pip

e #

194 t

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195 5

82510.0

11 1546532.6

35 1

037.3

67 pip

e #

195 t

op a

t bell

196 5

82531.3

77 1546532.5

65 1

037.0

75 pip

e #

196 t

op a

t bell

197 5

82553.3

53 1546532.7

36 1

036.8

59 pip

e #

197 t

op a

t bell

198 5

82574.7

93 1546532.9

97 1

036.7

59 pip

e #

198 t

op a

t bell

9+

00

10+

00

11+

001

2+

00

13

+0

014+

00

15

+0

016+

00

101+00100+00

F.O. F.O.

F.O.F.O.F.O.F.O.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

98th

ST

RE

ET

R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.TELETELETELETELETELETELETELETELETELETELE

TE

LE

98th

ST

RE

ET

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

66’

GRAVEL

66’

R.O.W.R.O.W.

12

0’

TELETELEGASGASGASGASGASF.O.F.O.F.O.ELECELECELECR.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.SANSANSANR.O.W.R.O.W.

City of Waukee

City of West Des Moines

4" W

PR

IV

AT

E

12" W (WDM)

17+

00

25’ TEMPORARY

EASEMENT

25’ TEMPORARY

EASEMENT

25’ PERMANENT

EASEMENT

F

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F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.

TE

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16"

12"

12"

F

CATV CATV CATV

SANSANSAN24" ST24" ST24" ST24" STxxxxxxxx

20’ PERMANENT

EASEMENT

70

’

30’

elev

1036.866

elev

1036.551

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1036.966

elev

1036.901

TS

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7+

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ST

RE

ET

ST

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10

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CT

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5-79-26

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8th

ST

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ET

P.I

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46 U

NIV

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P.I

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98

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TR

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100

101

103

104

105

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115

116

117

118

119

120

121

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296

297

29

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98

97

96

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67 1547114.9

29 1

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96 5

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43 1547093.1

33 1

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97 jo

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97 5

83197.9

52 1547071.5

14 1

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96 jo

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98 5

83198.1

08 1547051.0

71 1

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5 jo

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99 5

83198.2

47 1547028.4

34 1

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32 jo

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10

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8.9

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1

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8.9

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1

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69

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15 1546920.8

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67

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111 5

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5

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121 5

83199.7

88 1546551.7

1

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29 pip

e #

121 t

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5

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20

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6.8

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ref

ele

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297 5

83198.4

81 1546759.8

78 1

036.7

15 anode

298 5

83197.9

68 1546752.7

2 1

036.7

33 anode

299 5

83198.2

4 1546745.5

43 1

036.7

52 anode

16+00

10

1+

00

10

2+

00

10

3+

00

104+

00

10

5+

00

106+

00

107+

00

10

0+

00

STO

RM

STO

RM

F.O

.

24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST

F.O

.

F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

UN

IVE

RS

ITY

AV

E.

98th STREET

R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.TELE

TELE

66’

R.O.W.R.O.W.

42’

42’

42’

120’

60’

120’

TELETELECABLECABLECABLECABLECABLECABLECABLEF.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.GASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASF.O.F.O.F.O.F.O.F.O.F.O.ELECELECELECELECELECELECR.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.SANSANSANSANSANSANSANSANSANSANSANSANR.O.W.R.O.W.

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STO

RM

STO

RM

STO

RM

24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" STF.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.ELECELECR.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

UN

IVE

RS

ITY

AV

E.

96th STREET

42’

F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.R.O.W.R.O.W.R.O.W.R.O.W.

70’

42’

60’

120’

120’

CABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLEF.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.ELECGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASELECELECELECELECR.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.F.O.F.O.F.O.F.O.F.O.xxxxxxxxxxxxxxxxxxxxxxxSANSANSANSANSANSANSANSANSANSANSANSANSANSANSANSANSANSANSANR.O.W.R.O.W.15" ST

Cit

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25’ PERMANENT

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25’ TEMPORARY

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31 583185.8

46 1548484.1

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32 583185.3

99 1548462.1

48 1

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42 583186.2

18 1548257.2

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43 583186.5

28 1548236.1

79 1

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59 jo

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44 583186.6

87 1548214.0

43 1

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53 583190.6

44 1548023.9

59 1

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54 583191.6

55 1548004.5

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55

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56 583192.6

62 1547961.0

37 1

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57

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59 583193.5

23 1547895.2

47 1

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314 583182.4

25 1548404.1

81 1

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315 583181.9

82 1548412.3

05 1

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316 583181.7

36 1548419.9

39 1

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317 583186.8

38 1548414.5

02 1

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114+

00

11

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00

116+

00

117+

00

118+

00

119+

00

120+

00

12

1+

00

STO

RM

STO

RM

STO

RM

STO

RM

F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" STF.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.ELECELECR.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

Cit

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ELECR.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

94th STREET

Cit

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UN

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AV

E.

F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.

8" W (WDM)

12

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70’

2" B

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R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

120’

60’

120’

15" STCABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLECABLEF.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.GASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASELECELECELECELECR.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.xxxxxxxxxxxxxxxxxxxxR.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.SANSANSANSANSANSANSANSANSANSANSANSANSANSANSANSANSANSANR.O.W.R.O.W.15" ST15" ST

25’ PERMANENT

EASEMENT

25’ TEMPORARY

EASEMENT

30’ PERMANENT

EASEMENT

20’ TEMPORARY

EASEMENT

TELETELETELETELETELETELETELETELETELETELETELETELETELETELETELETELEELEC

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STO

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F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.

UN

IVE

RS

ITY

AV

E.

BOONE DRIVE

24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST24" ST15" STST24" ST24" ST24" STF.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.

!

R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

Cit

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f W

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Cit

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Cit

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Cit

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Des M

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W

92nd STREET

RO

AD

CO

NTRA

CTO

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C.

GO

V’T

LO

T 3

BK

. 826

PG

. 1057-1

060

GREER B

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PG

. 1057-1

060

TELER.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

120’

25’ PERMANENT

EASEMENT

45’ PERMANENT

EASEMENT

120’

60’

120’

15" ST15" STST24" ST24" ST24" ST24" ST24" ST24" ST24" STCABLECABLECABLECABLECABLECABLECABLEELECELECF.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.GASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASGASF.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.F.O.ELECR.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.SANSANSANSANSANSANSANSANSANSANSANSANSANSANSANR.O.W.

20’ TEMPORARY

EASEMENT

100’

20’ PERMANENT EASEMENT

12" W

(C

LIV

E)

12" W

(C

LIV

E)

12" W

(C

LIV

E)

12

" W

(W

DM

)

12" W

(W

DM

)

12" W (WDM)

12" W

(W

DM

)

30’ PERMANENT

EASEMENT

20’ TEMPORARY

EASEMENT

30’ PERMANENT

EASEMENT

20’ TEMPORARY

EASEMENT

TELETELETELETELETELETELETELETELETELETELETELETELETELETELETELETELE

F

ELECGASGASGASGASGASGASGASGASGASGAS

24" W

(D

MW

W) D

I

30" W

(D

MW

W) P

CC

P

R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.R.O.W.

CATV

CATVTELE

TELETELE

R.O

.W.

24" W (DMWW) DI

30" W (DMWW) PCCP

24" W (DMWW) DI

30" W (DMWW) PCCP

24"W

(D

MW

W)

DI

30

"W

(D

MW

W)

PC

CP

TS

ts3

18

TS

ts319

TS

ts320

266

265

26

4

263

324

322

PO

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Appendix C Standard CP/CM Test Procedures

Inspection Process for Flush Mounted Test Stations

What you’ll need:

• Inspection sheet and plan set (CP O&M) • Multimeter and portable Cu‐CuSO4 reference electrode • Can wrench, 10” crescent wrench • Milwaukee Key • Mallet and pry bar (for tough test station lids) • Wire strippers, wire crimpers, flat head screw driver • extra test station terminals • extra test station nuts, bolts and washers • Metal detector • Bug repellant!

Rural flush mounted test stations are marked with tri‐view posts. (I.e. the Joint Eastside Feeder Main)

Anode Test Stations (ATS) – Older Model

Calibrated Resistor (shunt)

Connected to water main

Connected to buried Cu‐CuSO4 Reference Electrode

Connected to Anode Field

Make minor repairs such as tightening bolts and re‐connecting wires to terminals as necessary.


Anode Test Stations (ATS) – Newer Model Calibrated Resistor

(shunt) Connected to water main

Connected to buried Cu‐CuSO4

Reference Electrode

Connected to Anode Field

Inspection Procedure

1. Set the multimeter to 2V DC. 2. Measure the current output of the anode field while it is on. (ON P/S) Attach the red cable

from the multimeter to the Cu‐CuSO4 Reference Cell and black cable from the multimeter to one of the cables connected via the shunt. Because the anode field and water main are electrically connected via the metal shunt, testing either cable will yield the same results.


3. Measure the local interrupted instant‐off potentials (I‐O P/S). • Temporarily disconnect one of the cables that are connected via the metal shunt. Attach

the red cable from the multimeter to the reference electrode and the black cable from the multimeter to the water main wire. The different wires connected to the water main should yield the same results. This reading is the I‐O P/S.

• With the Cathodic Protection disconnected measure the Anode Output. Connect the red wire from the multimeter to the reference cell and the black cable to the anode field.

(This is the water main) (This is the anode)

4. Repeat measurements using a portable Cu‐CuSO4 reference electrode to verify the permanent reference electrode at the test station is functioning properly. The readings with the portable reference electrode should have approximately the same shift (between the ON P/S and I‐O P/S) as the permanent reference electrode if it is functioning properly.


5. Measure the Anode Current. • Set Multimeter to 200mV DC. • Attach meter V‐Ω lead (red wire) to structure side of wire shunt. Attach meter

COM lead (black wire) to anode side of wire shunt. • Multiply mV reading by shunt factor (see below). • The voltage drop across a calibrated resistor (shunt) can be used in conjunction with

Ohm’s Law (Voltage = Current x Resistance). Substituting the measured voltage drop across the tips of the shunt and inserting the known resistance of the shunt allows an algebraic solution for the current to be calculated. This method does not involve breaking the Cathodic protection circuit1. See Dwg. # TP‐2 in Appendix C of the CP O&M for resistance factors.

Example: Wire Shunt resistance factor is 0.01 ohm 07.8 mV * 1amp/10mV = 0.78 amps = 780 mA

1 Testing Procedures‐ Cathodic Protection Commissioning Survey for CSPI Ref. 2005‐P10, Jeff Schramuk


Isolation Test Stations (ITS) and Casing Test Stations (CTS) – Older Model The wiring on the terminal board in the ITS and CTS are the same.


Connected to the Flange Isolation Kits (FIK) or the Casing

Connected to buried Cu‐CuSO4 Reference Electrode

Isolation Test Stations (ITS) and Casing Test Stations (CTS) – Newer Model The wiring on the terminal board in the ITS and CTS are the same.





Reference Electrode

1. Take the reading from the water main (ON P/S).

• Connect the red wire from the multimeter to the buried reference electrode (black wire).

• Connect the black wire from the multimeter to the water main (blue wire). 2. Take the reading from the flange isolation kit or casing (Foreign Structure).


• Connect the black wire from the multimeter to the FIK or casing (white wire). 3. Repeat measurements using a portable Cu‐CuSO4 reference electrode to verify the permanent

reference electrode at the test station is functioning properly.

Inspection Process for Post Mounted Test Stations

What you’ll need:

• Inspection sheet and plan set (CP O&M) • Multimeter and portable Cu‐CuSO4 reference electrode • Can wrench • Milwaukee Key • Mallet and pry bar (for tough test station lids) • Wire strippers, wire crimpers, flat head screw driver • extra test station terminals • extra test station nuts, bolts and washers • Metal detector • Bug repellant!

Anode Test Stations (ATS)

Calibrated Resistor (shunt)

Connected to water main (blue)

Connected to water main or Anode field

Connected to water main or Anode field


Reference Electrode

Make minor repairs such as tightening bolts and re‐connecting wires to terminals as necessary.


Inspection Procedure

1. Set the multimeter to 2V DC. 2. Measure the current output of the anode field while it is on. (ON P/S) Attach the red cable

from the multimeter to the Cu‐CuSO4 Reference Cell and black cable from the multimeter to one of the cables connected via the shunt. Because the anode field and water main are electrically connected via the metal shunt, testing either cable will yield the same results.

3. Measure the local interrupted instant‐off potentials (I‐O P/S). • Temporarily disconnect one of the cables that are connected via the metal shunt. Attach

the red cable from the multimeter to the reference electrode and the black cable from the multimeter to the water main wire. The different wires connected to the water main should yield the same results. This reading is the I‐O P/S.

• With the Cathodic Protection disconnected measure the Anode Output. Connect the red wire from the multimeter to the reference cell and the black cable to the anode field.

(This is the anode) (This is the water main)


4. Repeat measurements using a portable Cu‐CuSO4 reference electrode to verify the permanent reference electrode at the test station is functioning properly. The readings with the portable reference electrode should have approximately the same shift (between the ON P/S and I‐O P/S) as the permanent reference electrode if it is functioning properly.

Portable Cu‐CuSO4 Reference Electrode

5. Measure the Anode Current. • Set Multimeter to 200mV DC. • Attach meter V‐Ω lead (red wire) to structure side of wire shunt. Attach meter

COM lead (black wire) to anode side of wire shunt. • Multiply mV reading by shunt factor (see below). • The voltage drop across a calibrated resistor (shunt) can be used in conjunction with

Ohm’s Law (Voltage = Current x Resistance). Substituting the measured voltage drop across the tips of the shunt and inserting the known resistance of the shunt allows an algebraic solution for the current to be calculated. This method does not involve breaking the Cathodic protection circuit1. See Dwg. # TP‐2 in Appendix C of the CP O&M for resistance factors.

Example: Wire Shunt resistance factor is 0.01 ohm 00.3 mV * 1amp/10mV = 0.03 amps = 30 mA

1 Testing Procedures‐ Cathodic Protection Commissioning Survey for CSPI Ref. 2005‐P10, Jeff Schramuk


Isolation Test Stations (ITS) and Casing Test Stations (CTS) The wiring on the terminal board in the ITS and CTS are the same.


Reference Electrode



1. Take the reading from the water main (ON P/S).


• Connect the black wire from the multimeter to the water main (blue wire).

2. Take the reading from the flange isolation kit or casing (Foreign Structure). • Connect the red wire from the multimeter to the buried reference electrode (black

wire). • Connect the black wire from the multimeter to the FIK or casing (white wire).

3. Repeat measurements using a portable Cu‐CuSO4 reference electrode to verify the permanent

reference electrode at the test station is functioning properly.

INSTRUCTIONS 1. Attach meter V-Ω positive lead to Cu-

CuSO4 reference electrode. 2. Attach meter COM lead to pipe lead wire. 3. Select 200 DC mV scale on meter dial. 4. Record DC mV displayed on meter. 5. By convention, CP data is reported as

“negative” to reference electrode.

V-Ω COM A 10A

DCV ACV

DCA ACA

Ω

Soil surface (not pavement)

Portable Cu-CuSO4 Reference Electrode

(Placed directly over pipe)

Insulated Test Wires Run to Test Station

Underground Pipeline

Buried Cu-CuSO4 Reference Electrode

Scale: NoneDwg. #: TP-1Date: 2009-Dec-16 Rev. 0

Measuring Pipe-to-Soil Potential versus Standard Reference Electrode (Portable or Buried)and Multi-Meter

V-Ω COM A 10A

DCV ACV

DCA ACA

Ω

I

shunt tabs

shunt tabs

Underground Pipeline

Insulated Test Wires Run to Test Station

Calibrated Shunt Resistor


Measuring DC Current in Parallel through a Calibrated Shunt Resistor and Multi-Meter

INSTRUCTIONS 1. Attach meter Amp lead to pipe lead wire. 2. Attach meter COM lead to anode lead wire. 3. Select 2 DCA scale on meter dial. 4. Record DC amps displayed on meter.

I

V-Ω COM A 10A

DCV ACV

DCA ACA

Ω


Measuring DC Current in Series through a Multi-Meter

mA

.8.6.4

1.2

0

ZERO

TESTON

ADJ.

OFF

INSULATION CHECKER

Scale: NoneDwg. #: TP-6.ADate: 2009-Dec-03 Rev. 0

Test Instrument for ExposedFlange Isolation Gasket & BoltsTest Procedure Circuit #1Verify Flange Gasket Isolation

Circuit #1 Test Probes

Refer to Drawing TP-6.C for Specific Test Procedure Steps

Isolation Gasket

Isolation Bolt Sleeve

Isolation Washer

Scale: NoneDwg. #: TP-6.BDate: 2009-Dec-03 Rev. 0

Test Instrument for ExposedFlange Isolation Gasket & BoltsTest Procedure Circuit #2Verify Flange Bolt Isolation

mA

.8.6.4

1.2

0

ZERO

TESTON

ADJ.

OFF

INSULATION CHECKER

Circuit #2 Test Probes

Refer to Drawing TP-6.C for Specific Test Procedure Steps

Isolation Gasket

Isolation Bolt Sleeve

Isolation Washer

Scale: NoneDwg. #: TP-6.CDate: 2009-Dec-03 Rev. 0

Test Instrument for ExposedFlange Isolation Gasket & BoltsCircuit #1& 2Specific Test Procedures

Battery Test (Circuit #1 and #2) 1. Remove the plastic probe guards. 2. Move left hand toggle switch to the "ON" position. 3. Turn the potentiometer until the meter pointer goes full scale. 4. If the meter scale will not go full scale, the two "C" cell batteries must be replaced.

Circuit # 1: Flange Gasket Test Procedure (CPSI Dwg. TP-6.A) Instrument Adjustment:

1. Turn instrument "ON" with the left hand toggle switch. 2. Flip the right hand toggle switch to the "Zero" position. 3. Adjust the potentiometer knob until pointer is at "Zero." 4. Flip the right hand toggle switch to the "Test Position,” (pointer will jump hard to the right

pointer stop). 5. An occasional check may be made shorting across the probes with a screwdriver, knife etc. This

should show a direct short deflecting the pointer to "Zero" or below.

Flange Gasket Test Procedure: Make contact with each probe across the gasket in question. 1. A gasket that is good will read full scale. 2. If a gasket is shorted, the meter pointer will be deflected to or near to "Zero."

Circuit # 2: Flange Bolt Test Procedure (CPSI Dwg. TP-6.B) Instrument Adjustment:

1. With the instrument turned on, put the right hand toggle switch to the "Test" position. 2. Touch (short) the flexible test probe to the right hand fixed probe (marked with a dot) on the

face plate. 3. Adjust the potentiometer until the pointer goes past "Zero" and just touches the left hand

meter stop. This allows for the additional length of the test lead. 4. Break contact between the points - the pointer will jump hard to the right hand meter stop.

Locating a shorted flange bolt (Method 1):

1. After adjusting the instrument, on a double insulated flange unit, make contact from one flange to the bolt on the opposite flange.

2. On a single insulated flange (where the bolts are insulated through one flange only) makecontact with one probe on the insulated flange and the other probe on the bolt on the sameside of the flange unit.

3. If an insulated flange unit shows a definite short but each bolt indicates it is insulated, theshort exists across the flange gasket.

Locating a shorted flange bolt (Method 2):

1. After adjusting the instrument, with the probes making contact across the flanges, adjust themeter pointer to 50 on the meter scale.

2. Walk the instrument around the flanges at each bolt location carefully watching the meterindication.

3. The shorted bolt or bolts exist at the point of lowest reading.


Appendix D NACE International Standards

StandardTest Method

Measurement Techniques Related to Criteria forCathodic Protection on Underground or

Submerged Metallic Piping Systems

This NACE International standard represents a consensus of those individual members who havereviewed this document, its scope, and provisions. Its acceptance does not in any respectpreclude anyone, whether he has adopted the standard or not, from manufacturing, marketing,purchasing, or using products, processes, or procedures not in conformance with this standard.Nothing contained in this NACE International standard is to be construed as granting any right, byimplication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, orproduct covered by Letters Patent, or as indemnifying or protecting anyone against liability forinfringement of Letters Patent. This standard represents minimum requirements and should in noway be interpreted as a restriction on the use of better procedures or materials. Neither is thisstandard intended to apply in all cases relating to the subject. Unpredictable circumstances maynegate the usefulness of this standard in specific instances. NACE International assumes noresponsibility for the interpretation or use of this standard by other parties and acceptsresponsibility for only those official NACE International interpretations issued by NACEInternational in accordance with its governing procedures and policies which preclude theissuance of interpretations by individual volunteers.

Users of this NACE International standard are responsible for reviewing appropriate health, safety,environmental, and regulatory documents and for determining their applicability in relation to thisstandard prior to its use. This NACE International standard may not necessarily address allpotential health and safety problems or environmental hazards associated with the use ofmaterials, equipment, and/or operations detailed or referred to within this standard. Users of thisNACE International standard are also responsible for establishing appropriate health, safety, andenvironmental protection practices, in consultation with appropriate regulatory authorities ifnecessary, to achieve compliance with any existing applicable regulatory requirements prior to theuse of this standard.

CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may berevised or withdrawn at any time without prior notice. NACE International requires that action betaken to reaffirm, revise, or withdraw this standard no later than five years from the date of initialpublication. The user is cautioned to obtain the latest edition. Purchasers of NACE Internationalstandards may receive current information on all standards and other NACE Internationalpublications by contacting the NACE International Membership Services Department, 1440 SouthCreek Drive, Houston, Texas 77084-4906 (telephone +1 281/228-6200).

Reaffirmed 2002-04-11Approved 1997-12-22

NACE International1440 South Creek Drive

Houston, Texas 77084-4906+1 281/228-6200

ISBN 1-57590-047-5©2002, NACE International

NACE Standard TM0497-2002Item No. 21231

TM0497-2002

NACE International i

________________________________________________________________________

Foreword

This NACE International standard test method provides descriptions of the measurementtechniques and cautionary measures most commonly used on underground piping to determinewhether a specific criterion has been complied with at a test site. This test method includes onlythose measurement techniques that relate to the criteria or special conditions, such as a netprotective current, contained in NACE Standard RP0169.1 This test method is intended for use bycorrosion control personnel concerned with the corrosion of buried underground or submergedpiping systems, including oil, gas, water, and similar structures.

The measurement techniques described require that the measurements be made in the field.Because the measurements are obtained under widely varying circumstances of field conditionsand pipeline design, this standard is not as prescriptive as those NACE standard test methods thatuse laboratory measurements. Instead, this standard gives the user latitude to make testingdecisions in the field based on the technical facts available.

This standard contains instrumentation and general measurement guidelines. It includes methodsfor voltage drop considerations when making pipe-to-electrolyte potential measurements andprovides guidance to prevent incorrect data from being collected and used.

The measurement techniques provided in this standard were compiled from information submittedby committee members and others with expertise on the subject. Variations or other techniquesnot included may be equally effective. The complexity and diversity of environmental conditionsmay require the use of other techniques.

Appendix A contains information on the common types, use, and maintenance of referenceelectrodes. Appendix B contains information for the net protective current technique, which, whilenot a criterion, is a useful technique to reduce corrosion. Appendix C contains informationregarding the use of coupons to evaluate cathodic protection. While some engineers use thesetechniques, they are not universally accepted practices. However, there is ongoing research intotheir use.

The test methods in this standard were originally prepared by NACE Task Group T-10A-3 on TestMethods and Measurement Techniques Related to Cathodic Protection Criteria, a component ofUnit Committee T-10A on Cathodic Protection. It was reviewed by Task Group 020 and reaffirmedin 2002 by Specific Technology Group (STG) 35 on Pipelines, Tanks, and Well Casings. Thisstandard is issued by NACE under the auspices of STG 35.

In NACE standards, the terms shall, must, should, and may are used in accordance with thedefinitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shalland must are used to state mandatory requirements. Should is used to state that which is consideredgood and is recommended but is not absolutely mandatory. May is used to state that which isconsidered optional.

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TM0497-2002

ii NACE International

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NACE InternationalStandard

Test Method

Measurement Techniques Related to Criteriafor Cathodic Protection on Undergroundor Submerged Metallic Piping Systems

Contents

1. General......................................................................................................................... 12. Definitions..................................................................................................................... 13. Safety Considerations .................................................................................................. 34. Instrumentation and Measurement Guidelines............................................................. 35. Pipe-to-Electrolyte Potential Measurements ................................................................ 46. Causes of Measurement Errors ................................................................................... 77. Voltage Drops Other Than Across the Pipe Metal/Electrolyte Interface....................... 88. Test Method 1—Negative 850 mV Pipe-to-Electrolyte Potential

of Steel and Cast Iron Piping With Cathodic Protection Applied ................................ 109. Test Method 2—Negative 850 mV Polarized Pipe-to-Electrolyte

Potential of Steel and Cast Iron Piping....................................................................... 1110. Test Method 3—100 mV Cathodic Polarization

of Steel, Cast Iron, Aluminum, and Copper Piping..................................................... 13References........................................................................................................................ 17Bibliography ...................................................................................................................... 17Appendix A: Reference Electrodes .................................................................................. 18Appendix B: Net Protective Current ................................................................................. 19Appendix C: Using Coupons to Determine Adequacy of Cathodic Protection................. 25FiguresFigure 1: Instrument Connections...................................................................................... 6Figure 2: Pipe-to-Electrolyte Potential Corrections for Pipeline Current Flow.................... 9Figure 3: Cathodic Polarization Curves............................................................................ 14Figure B1: Surface Potential Survey................................................................................ 23Figure B2: Pipe-to-Electrolyte Potential Survey of a

Noncathodically Protected Pipeline............................................................................. 24

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Section 1: General

1.1 This standard provides testing procedures to complywith the requirements of a criterion at a test site on a buriedor submerged steel, cast iron, copper, or aluminum pipeline.

1.2 The provisions of this standard shall be applied bypersonnel who have acquired by education and relatedpractical experience the principles of cathodic protection ofburied and submerged metallic piping systems.

1.3 Special conditions in which a given test technique isineffective or only partially effective sometimes exist. Suchconditions may include elevated temperatures, disbondeddielectric or thermally insulating coatings, shielding,bacterial attack, and unusual contaminants in theelectrolyte. Deviation from this standard may be warrantedin specific situations. In such situations corrosion controlpersonnel should be able to demonstrate that adequatecathodic protection has been achieved.

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Section 2: Definitions(1)

Anode: The electrode of an electrochemical cell at whichoxidation occurs. Electrons flow away from the anode in theexternal circuit. Corrosion usually occurs and metal ionsenter the solution at the anode.

Cable: A bound or sheathed group of insulated conductors.

Cathode: The electrode of an electrochemical cell at whichreduction is the principal reaction. Electrons flow toward thecathode in the external circuit.

Cathodic Disbondment: The destruction of adhesionbetween a coating and the coated surface caused byproducts of a cathodic reaction.

Cathodic Polarization: The change of electrode potentialin the active (negative) direction caused by current acrossthe electrode/electrolyte interface. See also Polarization.

Cathodic Protection: A technique to reduce the corrosionof a metal surface by making that surface the cathode of anelectrochemical cell.

Cathodic Protection Coupon: A metal samplerepresenting the pipeline at the test site, used for cathodicprotection testing, and having a chemical compositionapproximating that of the pipe. The coupon size should besmall to avoid excessive current drain on the cathodicprotection system.

Coating: A liquid, liquefiable, or mastic composition that,after application to a surface, is converted into a solidprotective, decorative, or functional adherent film.

Conductor: A bare or insulated material suitable forcarrying electric current.

Corrosion: The deterioration of a material, usually a metal,that results from a reaction with its environment.

Corrosion Potential (Ecorr): The potential of a corrodingsurface in an electrolyte relative to a reference electrodeunder open-circuit conditions (also known as rest potential,open-circuit potential, or freely corroding potential).

Criterion: A standard for assessment of the effectivenessof a cathodic protection system.

Current Density: The current to or from a unit area of anelectrode surface.

Electrical Isolation: The condition of being electricallyseparated from other metallic structures or the environment.

Electrode: A conductor used to establish contact with anelectrolyte and through which current is transferred to orfrom an electrolyte.

Electrode Potential: The potential of an electrode in anelectrolyte as measured against a reference electrode.(The electrode potential does not include any resistancelosses in potential in either the electrolyte or the externalcircuit. It represents the reversible work to move a unitcharge from the electrode surface through the electrolyte tothe reference electrode.)

Electrolyte: A chemical substance containing ions thatmigrate in an electric field. (For the purpose of thisstandard, electrolyte refers to the soil or liquid, includingcontained moisture and other chemicals, next to and incontact with a buried or submerged metallic piping system.)

Foreign Structure: Any metallic structure that is notintended as part of a system under cathodic protection.

NACE International 1

___________________________(1) Definitions in this section reflect common usage among practicing corrosion control personnel and apply specifically to how terms are usedin this standard. As much as possible, these definitions are in accord with those in the “NACE Glossary of Corrosion-Related Terms”(Houston, TX: NACE).

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Free Corrosion Potential: See Corrosion Potential.

Galvanic Anode: A metal that provides sacrificialprotection to another metal that is more noble whenelectrically coupled in an electrolyte. This type of anode isthe current source in one type of cathodic protection.

Holiday: A discontinuity in a protective coating thatexposes unprotected surface to the environment.

Impressed Current: An electric current supplied by adevice employing a power source that is external to theelectrode system. (An example is direct current for cathodicprotection.)

“Instant Off” Potential: A measurement of a pipe-to-electrolyte potential made without perceptible delayfollowing the interruption of cathodic protection.

Interference: Any electrical disturbance on a metallicstructure as a result of stray current.

Isolation: See Electrical Isolation.

Long-Line Current: Current through the earth between ananodic and a cathodic area that returns along anunderground metallic structure.

Long-Line Current Voltage Drop Error: That voltage droperror in the “off” potential that is caused by current flow inthe soil due to potential gradients along the pipe surface.

“Off” or “On”: A condition whereby cathodic protectioncurrent is either turned off or on.

Pipe-to-Electrolyte Potential: The potential differencebetween the pipe metallic surface and electrolyte that ismeasured with reference to an electrode in contact with theelectrolyte. This measurement is commonly termed pipe-to-soil (P/S).

Pipe-to-Soil: See Pipe-to-Electrolyte Potential.

Polarization: The change from the open-circuit potential asa result of current across the electrode/electrolyte interface.

Polarized Potential: The potential across thestructure/electrolyte interface that is the sum of thecorrosion potential and the cathodic polarization.

Potential Gradient: A change in the potential with respectto distance, expressed in millivolts per unit of distance.

Protection Potential: A measured potential meeting therequirements of a cathodic protection criterion.

Reference Electrode: An electrode whose open-circuitpotential is constant under similar conditions of

measurement, which is used for measuring the relativepotentials of other electrodes.

Resistance to Electrolyte: The resistance of a structure tothe surrounding electrolyte.

Reverse-Current Switch: A device that prevents thereversal of direct current through a metallic conductor.

Shielding: Preventing or diverting the cathodic protectioncurrent from its intended path to the structure to beprotected.

Shorted Pipeline Casing: A casing that is in metalliccontact with the carrier pipe.

Side Drain Potential: A potential gradient measuredbetween two reference electrodes, one located over thepipeline and the other located a specified distance lateral tothe direction of the pipe.

Sound Engineering Practices: Reasoning exhibited orbased on thorough knowledge and experience, logicallyvalid, and having true premises showing good judgment orsense in the application of science.

Stray Current: Current through paths other than theintended circuit.

Telluric Current: Current in the earth that results fromgeomagnetic fluctuations.

Test Lead: A wire or cable attached to a structure forconnection of a test instrument to make cathodic protectionpotential or current measurements.

Voltage: An electromotive force or a difference in electrodepotentials expressed in volts.

Voltage Drop: The voltage across a resistance accordingto Ohm’s Law.

Voltage Spiking: A momentary surging of potential thatoccurs on a pipeline when the protective current flow froman operating cathodic protection device is interrupted orapplied. This phenomenon is the result of inductive andcapacitive electrical characteristics of the system and maybe incorrectly recorded as an “off” or “on” pipe-to-electrolytepotential measurement. This effect may last for severalhundred milliseconds and is usually larger in magnitudenear the connection of the cathodic protection device to thepipeline. An oscilloscope or similar instrument may benecessary to identify the magnitude and duration of thespiking.

Wire: A slender rod or filament of drawn metal. In practice,the term is also used for smaller gauge conductors (size 6mm2 [No. 10 AWG(2)] or smaller).

2 NACE International

___________________________(2) American Wire Gauge (AWG).

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Section 3: Safety Considerations

3.1 Appropriate safety precautions, including the following,shall be observed when making electrical measurements.

3.1.1 Be knowledgeable and qualified in electricalsafety precautions before installing, adjusting,repairing, removing, or testing impressed currentcathodic protection equipment.

3.1.2 Use properly insulated test lead clips andterminals to avoid contact with unanticipated highvoltage (HV). Attach test clips one at a time using asingle-hand technique for each connection.

3.1.3 Use caution when long test leads are extendednear overhead high-voltage alternating current (HVAC)power lines, which can induce hazardous voltages ontothe test leads. High-voltage direct current (HVDC)power lines do not induce voltages under normaloperation, but transient conditions may causehazardous voltages.

3.1.3.1 Refer to NACE Standard RP01772 foradditional information about electrical safety.

3.1.4 Use caution when making tests at electricalisolation devices. Before proceeding with further tests,use appropriate voltage detection instruments orvoltmeters with insulated test leads to determinewhether hazardous voltages may exist.

3.1.5 Avoid testing when thunderstorms are in thearea. Remote lightning strikes can create hazardousvoltage surges that travel along the pipe under test.

3.1.6 Use caution when stringing test leads acrossstreets, roads, and other locations subject to vehicularand pedestrian traffic. When conditions warrant, useappropriate barricades, flagging, and/or flag persons.

3.1.7 Before entering, inspect excavations andconfined spaces to determine that they are safe.Inspections may include shoring requirements forexcavations and testing for hazardous atmospheres inconfined spaces.

3.1.8 Observe appropriate electrical codes andapplicable safety regulations.

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Section 4: Instrumentation and Measurement Guidelines

4.1 Cathodic protection electrical measurements requireproper selection and use of instruments. Pipe-to-electrolytepotential, voltage drop, potential difference, and similarmeasurements require instruments that have appropriatevoltage ranges. The user should know the capabilities andlimitations of the equipment, follow the manufacturer’sinstruction manual, and be skilled in the use of electricalinstruments. Failure to select and use instruments correctlycauses errors in cathodic protection measurements.

4.1.1 Analog instruments are usually specified interms of input resistance or internal resistance. This isusually expressed as ohms per volt of full meter scaledeflection.

4.1.2 Digital instruments are usually specified in termsof input impedance expressed as megaohms.

4.2 Factors that may influence instrument selection for fieldtesting include:

(a) Input impedance (digital instruments);(b) Input resistance or internal resistance (analoginstruments);(c) Sensitivity;(d) Conversion speed of analog-to-digital converters usedin digital or data logging instruments;(e) Accuracy;

(f) Instrument resolution;(g) Ruggedness;(h) Alternating current (AC) and radio frequency (RF)signal rejection; and(i) Temperature and/or climate limitations.

4.2.1 Some instruments are capable of measuring andprocessing voltage readings many times per second.Evaluation of the input wave-form processing may berequired if an instrument does not give consistentresults.

4.2.2 Measurement of pipe-to-electrolyte potentials onpipelines affected by dynamic stray currents mayrequire the use of recording or analog instruments toimprove measurement accuracy. Dynamic straycurrents include those from electric railway systems,HVDC transmission systems, mining equipment, andtelluric currents.

4.3 Instrument Effects on Voltage Measurements

4.3.1 To measure pipe-to-electrolyte potentialsaccurately, a digital voltmeter must have a high inputimpedance (high internal resistance, for an analoginstrument) compared with the total resistance of themeasurement circuit.


TM0497-2002

4.3.1.1 An input impedance of 10 megaohms ormore should be sufficient for a digital meter. Aninstrument with a lower input impedance mayproduce valid data if circuit contact errors areconsidered. One means of making accuratemeasurements is to use a potentiometer circuit inan analog meter.

4.3.1.2 A voltmeter measures the potential acrossits terminals within its design accuracy. However,current flowing through the instrument createsmeasurement errors due to voltage drops thatoccur in all resistive components of ameasurement circuit.

4.3.2 Some analog-to-digital converters used in digitaland data logging instruments operate so fast that theinstrument may indicate only a portion of the inputwaveform and thus provide incorrect voltageindications.

4.3.3 Parallax errors on an analog instrument can beminimized by viewing the needle perpendicular to the

4

face of the instrument on the centerline projected fromthe needle point.

4.3.4 The accuracy of potential measurements shouldbe verified by using an instrument having two or moreinput impedances (internal resistance, for analoginstruments) and comparing potential values measuredusing different input impedances. If the measuredvalues are virtually the same, the accuracy isacceptable. Corrections need to be made if measuredvalues are not virtually identical. Digital voltmeters thathave a constant input impedance do not indicate ameasurement error by changing voltage ranges. Analternative is to use a meter with a potentiometercircuit.

4.4 Instrument Accuracy

4.4.1 Instruments shall be checked for accuracybefore use by comparing readings to a standardvoltage cell, to another acceptable voltage source, or toanother appropriate instrument known to be accurate.

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Section 5: Pipe-to-Electrolyte Potential Measurements

5.1 Instruments used to measure AC voltage, direct current(DC) voltage, or other electrical functions usually have oneterminal designated “Common” (COM). This terminal eitheris black in color or has a negative (-) symbol. The positiveterminal either is red in color or has a positive (+) symbol.The positive and negative symbols in the meter displayindicate the current flow direction through the instrument(Figure 1a). For example, a positive symbol in the meterdisplay indicates current flowing from the positive terminalthrough the meter to the negative terminal. One instrumenttest lead is usually black in color and the other red. Theblack test lead is connected to the negative terminal of theinstrument and the red lead to the positive terminal.

5.2 Voltage measurements should be made using thelowest practicable range on the instrument. A voltagemeasurement is more accurate when it is measured in theupper two-thirds of a range selected for a particularinstrument. Errors can occur, for example, when aninstrument with a 2-V range is used to measure a voltage of15 mV. Such a value might be a voltage drop caused bycurrent flowing in a metal pipeline or through a calibratedshunt. A much more accurate measurement would bemade using an instrument having a 20-mV range.

5.3 The usual technique to determine the DC voltageacross battery terminals, pipeline metal/electrolyte interface,or other DC system is to connect the black test lead to thenegative side of the circuit and the red test lead to thepositive side of the circuit. When connected in this manner,an analog instrument needle moves in an upscale

(clockwise) direction indicating a positive value with relationto the negative terminal. A digital instrument connected inthe same manner displays a digital value, usually precededby a positive symbol. In each situation the measuredvoltage is positive with respect to the instrument’s negativeterminal. (See instrument connections in Figure 1a.)

5.4 The voltage present between a reference electrode anda metal pipe can be measured with a voltmeter. Thereference electrode potential is normally positive withrespect to ferrous pipe; conversely the ferrous pipe isnegative with respect to the reference electrode.

5.5 A pipe-to-electrolyte potential is measured using a DCvoltmeter having an appropriate input impedance (orinternal resistance, for an analog instrument), voltagerange(s), test leads, and a stable reference electrode, suchas a saturated copper/copper sulfate (CSE), silver/silverchloride (Ag/AgCl), or saturated potassium chloride (KCl)calomel reference electrode. The CSE is usually used formeasurements when the electrolyte is soil or fresh waterand less often for salt water. When a CSE is used in ahigh-chloride environment, the stability (lack ofcontamination) of the CSE must be determined before thereadings may be considered valid. The Ag/AgCl referenceelectrode is usually used in seawater environments. Thesaturated KCl calomel electrode is used more often forlaboratory work. However, more-rugged, polymer-body,gel-filled saturated KCl calomel electrodes are available,though modifications may be necessary to increase contactarea with the environment.

NACE International

TM0497-2002

5.6 Meter Polarity

5.6.1 Pipe-to-electrolyte potentials are usuallymeasured by connecting the instrument negativeterminal to the pipe and the positive terminal to thereference electrode, which is in contact with the pipeelectrolyte. With this connection the instrumentindicates that the reference electrode is positive withrespect to the pipe. Because the reference electrodehas a positive value with respect to the pipe, the pipevoltage is negative with respect to the referenceelectrode (see Figure 1a). This negative pipe-to-electrolyte potential is the value used for NACE criteria.

5.6.2 Pipe-to-electrolyte potential measurements aresometimes made with the reference electrodeconnected to the instrument negative terminal and thepipeline to the positive terminal. Figure 1b illustratesthis connection.

5.6.2.1 If the instrument is a data logging device,the recorded data may be printed out with anegative symbol unless a polarity reversal occurs.

5.7 The pipe-to-electrolyte potential measurement of aburied pipe should be made with the reference electrodeplaced close to the metal/electrolyte interface of the pipe.The common practice, however, is to place the referenceelectrode as close to the pipe as practicable, which isusually at the surface of the earth above the centerline ofthe pipe. (See Figure 1a.) This measurement includes acombination of the voltage drops associated with the:

(a) Voltmeter;(b) Test leads;(c) Reference electrode;(d) Electrolyte;(e) Coating, if applied;(f) Pipe; and(g) Pipe metal/electrolyte interface.

5.8 The pipe-to-electrolyte potential measurement asdescribed above is a resultant of the:

(a) Voltage drop created by current flowing through theelectrical resistances of the items listed in Paragraph 5.7;and(b) For coated pipe, the influence of coating holidays,depending on their location, number, and size.

5.9 Pipe-to-electrolyte potential measurements made todetermine the level of cathodic protection at the test siteshould consider the following:

(a) Effectiveness of coatings, particularly those known orsuspected to be deteriorated or damaged;(b) Bare sections of pipe;(c) Bonds to mitigate interference;(d) Parallel coated pipelines, electrically connected andpolarized to different potentials;(e) Shielding;

(f) Effects of other structures on the measurements;(g) History of corrosion leaks and repairs;(h) Location of impressed current anodes;(i) Unknown, inaccessible, or direct-connected galvanicanodes;(j) Location of isolation devices, including high-resistancepipe connections and compression couplings;(k) Presence of electrolytes, such as unusual corrosives,chemical spills, extreme soil resistivity changes, acidicwaters, and contamination from sewer spills;(l) Location of shorted or isolated casings;(m) DC interference currents, such as HVDC, telluric,welding equipment, foreign rectifier, mining equipment, andelectric railway or transit systems;(n) Contacts with other metals or structures;(o) Locations where the pipe enters and leaves theelectrolyte;(p) Areas of construction activity during the pipelinehistory;(q) Underground metallic structures close to or crossingthe pipeline;(r) Valves and other appurtenances; and(s) HVAC overhead power lines.

5.10 Voltage drops other than those across the pipemetal/electrolyte interface shall be considered for validinterpretation of pipe-to-electrolyte voltage measurementsmade to satisfy a criterion. Measurement errors should beminimized to ensure reliable pipe-to-electrolyte potentialmeasurements.

5.11 The effect of voltage drops on a pipe-to-electrolytepotential measurement can be determined by interruptingall significant current sources and then making themeasurement. This measurement is referred to as an“instant-off” potential. The measurement must be madewithout perceptible delay after current interruption to avoidloss of polarization. The voltage value measured isconsidered to be the “polarized potential” of the pipe at thatlocation. Because the current interruption may cause avoltage spike, recording the spike as the “instant-offpotential” must be avoided. The magnitude and duration ofthe voltage spike can vary; however, the duration is usuallywithin 0.5 second. The following are examples of when itmay not be practical to interrupt all current sources to makethe “instant-off potential” measurement.

5.11.1 Galvanic Anodes

5.11.1.1 Galvanic anodes connected directly tothe pipe without benefit of aboveground teststations or connections. Interruption requiresexcavation of the connections.

5.11.2 Impressed Current Systems

5.11.2.1 Galvanic anodes directly connected topiping protected using an impressed currentsystem;

5.11.2.2 Multiple impressed current sources;


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-

DC

VOLT

COM

+

-

0.850

+

Pipe Test Lead

Voltmeters

+-

Direction of meter current+

ReferenceElectrode

CL

Electrode potentialdoes not vary

Pipe potentialis the variable

Pipe

0 1

Figure 1aInstrument Connection

Pipe Test Lead

Voltmeter

+-

Direction of meter current

ReferenceElectrode

CL

Electrode potentialdoes not vary

Pipe potentialis the variable

Pipe

DC

VOLT

COM

-

-

0.850

+

Figure 1bAlternative Instrument Connection

FIGURE 1Instrument Connections

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5.11.2.3 Impressed current devices on foreignpiping; and

5.11.2.4 Numerous cross bonds to parallelpipelines.

5.11.3 Natural and Manmade Stray Currents

5.11.3.1 Telluric currents; and

5.11.3.2 Manmade DC stray currents, such asthose from mass transit and mining operations.

5.12 When voltage drops have been evaluated at a testlocation and the pipe-to-electrolyte potential found to besatisfactory, the “on” pipe-to-electrolyte potential value maybe used for monitoring until significant environmental,structural, or cathodic protection system parameterschange.

5.12.1 Significant environmental, structural, orcathodic protection system parameter changes mayinclude:

(a) Replacement or addition of piping;(b) Addition, relocation, or deterioration of cathodicprotection systems;(c) Failure of electrical isolating devices;(d) Effectiveness of coatings; and(e) Influence of foreign structures.

5.13 After a cathodic protection system is operating, timemay be required for the pipe to polarize. This should beconsidered when measuring the potential at a test site on anewly protected pipe or after reenergizing a cathodicprotection device.

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Section 6: Causes of Measurement Errors

6.1 Factors that contribute to faulty potentialmeasurements include:

6.1.1 Pipe and instrument test leads

(a) Broken or frayed wire strands (may not be visibleinside the insulation);(b) Damaged or defective test lead insulation thatallows the conductor to contact wet vegetation, theelectrolyte, or other objects;(c) Loose, broken, or faulty pipe or instrumentconnections; and(d) Dirty or corroded connection points.

6.1.2 Reference electrode condition and placement

(a) Contaminated reference electrode solution orrod, and solutions of insufficient quantity or saturation(only laboratory-grade chemicals and distilled water, ifwater is required, should be used in a referenceelectrode);(b) Reference electrode plug not sufficiently porousto provide a conductive contact to the electrolyte;(c) Porous plug contaminated by asphalt, oil, orother foreign materials;(d) High-resistance contact between referenceelectrode and dry or frozen soil, rock, gravel,vegetation, or paving material;(e) Reference electrode placed in the potentialgradient of an anode;(f) Reference electrode positioned in the potentialgradient of a metallic structure other than the one withthe potential being measured;(g) Electrolyte between pipe and disbonded coatingcausing error due to electrode placement in electrolyteon opposite side of coating;

(h) Defective permanently installed referenceelectrode;(i) Temperature correction not applied whenneeded; and(j) Photo-sensitive measurement error (in CSE witha clear-view window) due to light striking the electrodeelectrolyte solution (photovoltaic effect).

6.1.3 Unknown isolating devices, such as unbondedtubing or pipe compression fittings, causing the pipe tobe electrically discontinuous between the testconnection and the reference electrode location.

6.1.4 Parallel path inadvertently established by testpersonnel contacting instrument terminals or metallicparts of the test lead circuit, such as test lead clips andreference electrodes, while a potential measurement isbeing made.

6.1.5 Defective or inappropriate instrument, incorrectvoltage range selection, instrument not calibrated orzeroed, or a damp instrument sitting on wet earth.

6.1.6 Instrument having an analog-to-digital converteroperating at such a fast speed that the voltage spikesproduced by current interruption are indicated insteadof the actual “on” and “off” values.

6.1.7 Polarity of the measured value incorrectlyobserved.

6.1.8 Cathodic protection current-carrying conductorused as a test lead for a pipe potential measurement.


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6.1.9 Interference

6.1.9.1 Electromagnetic interference or inductionresulting from AC power lines or radio frequencytransmitters inducing test lead and/or instrumenterrors. This condition is often indicated by a fuzzy,fluctuating, or blurred pointer movement on ananalog instrument or erratic displays on digitalvoltmeters. A DC voltmeter must have sufficientAC rejection capability, which can be determinedby referring to the manufacturer’s specification.

6.1.9.2 Telluric or stray DC currents flowingthrough the earth and piping.

6.2 Reference electrode contact resistance is reduced by:

6.2.1 Soil moisture—If the surface soil is so dry thatthe electrical contact of the reference electrode with the

electrolyte is impaired, the soil around the electrodemay be moistened with water until the contact isadequate.

6.2.2 Contact surface area—Contact resistance maybe reduced by using a reference electrode with a largercontact surface area.

6.2.3 Frozen soil—Contact resistance may be reducedby removing the frozen soil to permit electrode contactwith unfrozen soil.

6.2.4 Concrete or asphalt-paved areas—Contactresistance may be reduced by drilling through thepaving to permit electrode contact with the soil.

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Section 7: Voltage Drops Other Than Across the Pipe Metal/Electrolyte Interface

7.1 Voltage drops that are present when pipe-to-electrolytepotential measurements are made occur in the following:

7.1.1 Measurement Circuit—The voltage drop otherthan across the pipe metal/electrolyte interface in themeasurement circuit is the sum of the individualvoltage drops caused by the meter current flow throughindividual resistances that include:

(a) Instrument test lead and connection resistances;(b) Reference electrode internal resistance;(c) Reference electrode-to-electrolyte contactresistance;(d) Coating resistance;(e) Pipe metallic resistance;(f) Electrolyte resistance;(g) Analog meter internal resistance; and(h) Digital meter internal impedance.A measurement error occurs if the analog meterinternal resistance or the digital meter internalimpedance is not several orders of magnitude higherthan the sum of the other resistances in themeasurement circuit.

7.1.2 Pipe—Current flowing within the pipe wallcreates a voltage drop. This voltage drop and thedirection of the current shall be considered when thereference electrode is not near the pipe connection andsignificant current is conducted by the pipe.Consideration is needed because an error in the pipe-to-electrolyte potential measurement will occur if thepipe current causes a significant voltage drop. Currentdirected to the pipe connection from the referenceelectrode causes the measured potential to be morenegative by the amount of the pipe current voltage drop(see Figure 2a). Conversely, the potential is lessnegative by that amount if the pipe current direction is

from the pipe connection to the reference electrode(see Figure 2b).

7.1.3 Electrolyte—When a pipe-to-electrolyte potentialis measured with cathodic protection current applied,the voltage drop in the electrolyte between thereference electrode and the metal/electrolyte interfaceshall be considered. Measurements taken close tosacrificial or impressed current anodes can contain alarge voltage drop. Such a voltage drop can consist of,but is not limited to, the following:

(a) A voltage drop caused by current flowing tocoating holidays when the line is coated; and(b) A voltage drop caused by large voltage gradientsin the electrolyte that occur near operating anodes(sometimes termed “raised earth effect”).

7.1.3.1 Testing to locate galvanic anodes bymoving the reference electrode along thecenterline of the line may be necessary when thelocations are not known.

7.1.4 Coatings—Most coatings provide protection tothe pipe by reducing the pipe surface contact with theenvironment. Due to the relative ionic impermeabilityof coatings, they resist current flow. While theinsulating ability of coatings reduces the currentrequired for cathodic protection, coatings are notimpervious to current flowing through them. Currentflow through the coating causes a voltage drop that isgreater than when the pipe is bare, under the sameenvironmental conditions.

7.2 Specialized equipment that uses various techniques tomeasure the impressed current wave form and to calculatea pipe-to-electrolyte potential free of voltage drop is


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available. This equipment may minimize problems resultingfrom spiking effects, drifting of interrupters, and current fromother DC sources.


+_

PIPE METAL VOLTAGE DROP

PIPELINE CURRENT

PIPE TESTCONNECTION

REFERENCEELECTRODE

VOLTMETER

ADD PIPE METAL VOLTAGE DROP TO PIPE-TO-ELECTROLYTEMEASUREMENT WHEN CURRENT IS TOWARD PIPE CONTACT

Figure 2aCorrection When Pipeline Current Flows Toward Pipe Test Connection

+_

PIPE METAL VOLTAGE DROP

PIPELINE CURRENT

PIPE TESTCONNECTION

REFERENCEELECTRODE

VOLTMETER

SUBTRACT PIPE METAL VOLTAGE DROP FROM PIPE-TO-ELECTROLYTEMEASUREMENT WHEN CURRENT IS AWAY FROM PIPE CONTACT

Figure 2bCorrection When Pipeline Current Flows Away from Pipe Test Connection

FIGURE 2Pipe-to-Electrolyte Potential Corrections for Pipeline Current Flow

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Section 8: Test Method 1—Negative 850 mV Pipe-to-Electrolyte Potentialof Steel and Cast Iron Piping with Cathodic Protection Applied

8.1 Scope

Test Method 1 describes a procedure to assess theadequacy of cathodic protection on a steel or cast ironpipeline according to the criterion stated in NACE StandardRP0169,1 Paragraph 6.2.2.1.1:

A negative (cathodic) potential of at least 850 mV withthe cathodic protection applied. This potential ismeasured with respect to a saturated copper/coppersulfate reference electrode (CSE) contacting theelectrolyte. Voltage drops other than those across thestructure-to-electrolyte boundary must be consideredfor valid interpretation of this voltage measurement.

NOTE: Consideration is understood to mean theapplication of sound engineering practice indetermining the significance of voltage drops bymethods such as:

(a) Measuring or calculating the voltage drop(s);(b) Reviewing the historical performance of thecathodic protection system;(c) Evaluating the physical and electricalcharacteristics of the pipe and its environment; and(d) Determining whether there is physical evidence ofcorrosion.

8.2 General

8.2.1 Cathodic protection current shall remain “on”during the measurement process. This potential iscommonly referred to as the “on” potential.

8.2.2 Test Method 1 measures the pipe-to-electrolytepotential as the sum of the polarized potential and anyvoltage drops in the circuit. These voltage dropsinclude those through the electrolyte and pipelinecoating from current sources such as impressedcurrent, galvanic anodes, and telluric effects.

8.2.3 Because voltage drops other than those acrossthe pipe metal/electrolyte interface may be included inthis measurement, these drops shall be considered, asdiscussed in Paragraph 8.6.

8.3 Comparison with Other Methods

8.3.1 Advantages

(a) Minimal equipment, personnel, and vehicles arerequired; and(b) Less time is required to make measurements.

8.3.2 Disadvantages

(a) Potential measured includes voltage drops otherthan those across the pipe metal/electrolyte interface;and(b) Meeting the requirements for considering thesignificance of voltage drops (see Paragraph 8.6) canresult in added time to assess adequacy of cathodicprotection at the test site.

8.4 Basic Test Equipment

8.4.1 Voltmeter with adequate input impedance.Commonly used digital instruments have a nominalimpedance of 10 megaohms. An analog instrumentwith an internal resistance of 100,000 ohms per voltmay be adequate in certain circumstances in which thecircuit resistance is low. A potentiometer circuit may benecessary in other instances.

8.4.2 Two color-coded meter leads with clips forconnection to the pipeline and reference electrode.

8.4.3 Reference Electrode

8.4.3.1 CSE.

8.4.3.2 Other standard reference electrodes maybe substituted for the CSE. These referenceelectrodes are described in Appendix A,Paragraph A2.

8.5 Procedure

8.5.1 Before the test, verify that cathodic protectionequipment has been installed and is operatingproperly. Time should be allowed for the pipelinepotentials to reach polarized values.

8.5.2 Determine the location of the site to be tested.Selection of a site may be based on:

(a) Location accessible for future monitoring;(b) Other protection systems, structures, and anodesthat may influence the pipe-to-electrolyte potential;(c) Electrical midpoints between protective devices;(d) Known location of an ineffective coating if the lineis coated; and(e) Location of a known or suspected corrosiveenvironment.

8.5.3 Make electrical contact between the referenceelectrode and the electrolyte at the test site, directlyover the centerline of the pipeline or as close to it as ispracticable.


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8.5.4 Connect the voltmeter to the pipeline andreference electrode as described in Paragraph 5.6.

8.5.5 Record the pipe-to-electrolyte potential and itspolarity with respect to the reference electrode.

8.6 Considering the Significance of Voltage Drops for ValidInterpretation of the Criterion

8.6.1 The significance of voltage drops can beconsidered by:

8.6.1.1 Comparing historical levels of cathodicprotection with physical evidence from the pipelineto determine whether corrosion has occurred.

8.6.1.2 Comparing soil corrosiveness withphysical evidence from the pipeline to determinewhether corrosion has occurred.

8.6.2 Physical evidence of corrosion is determined byevaluating items such as:

(a) Leak history data;

(b) Buried pipeline inspection report data regardinglocations of coating failures, localized conditions ofmore-corrosive electrolyte, or substandard cathodicprotection levels have been experienced; and/or(c) Verification of in-line inspection-tool metal lossindications by follow-up excavation of anomalies andinspection of the pipe external surface.

8.6.3 Cathodic protection shall be judged adequate atthe test site if:

(a) The pipe-to-electrolyte potential measurement isnegative 850 mV, or more negative, with respect to aCSE; and(b) The significance of voltage drops has beenconsidered by applying the principles described inParagraphs 8.6.1 or 8.6.2.

8.7 Monitoring

When the significance of a voltage drop has beenconsidered at the test site, the measured potentials may beused for monitoring unless significant environmental,structural, coating integrity, or cathodic protection systemparameters have changed.

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Section 9: Test Method 2—Negative 850 mV Polarized Pipe-to-ElectrolytePotential of Steel and Cast Iron Piping

9.1 Test Method 2 describes the most commonly used testmethod to satisfy this criterion (see Paragraph 9.2). Thismethod uses current interruption to determine whethercathodic protection is adequate at the test site according tothe criterion.

9.2 Scope

This method uses an interrupter(s) to eliminate the cathodicprotection system voltage drop from the pipe-to-electrolytepotential measurement for comparison with the criterionstated in NACE Standard RP0169,1 Paragraph 6.2.2.1.2:

A negative polarized potential of at least 850 mVrelative to a saturated copper/copper sulfate referenceelectrode (CSE).

9.3 General

9.3.1 Interrupting the known cathodic protectioncurrent source(s) eliminates voltage drops associatedwith the protective currents being interrupted.However, significant voltage drops may also occurbecause of currents from other sources, as discussedin Section 7.

9.3.2 To avoid significant depolarization of the pipe,the “off” period should be limited to the time necessary

to make an accurate potential measurement. The “off”period is typically less than 3 seconds.

9.3.3 The magnitude and duration of a voltage spikecaused by current interruption can vary, but theduration is typically within 0.5 second. After the currentis interrupted, the time elapsed until the measurementis recorded should be long enough to avoid errorscaused by voltage spiking. On-site measurements withappropriate instruments may be necessary todetermine the duration and magnitude of the spiking.

9.3.4 Current sources that can affect the accuracy ofthis test method include the following:

(a) Unknown, inaccessible, or direct-connectedgalvanic anodes;(b) Cathodic protection systems on associatedpiping or foreign structures;(c) Electric railway systems;(d) HVDC electric power systems;(e) Telluric currents;(f) Galvanic, or bimetallic, cells;(g) DC mining equipment;(h) Parallel coated pipelines, electrically connectedand polarized to different potentials;(i) Uninterrupted current sources;(j) Unintentional connections to other structures orbonds to mitigate interference; and(k) Long-line currents.


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9.4 Comparison with Other Methods

9.4.1 Advantages

(a) Voltage drops associated with the protectivecurrents being interrupted are eliminated.

9.4.2 Disadvantages

(a) Additional equipment is required;(b) Additional time, personnel, and vehicles may berequired to set up equipment and to make pipe-to-electrolyte potential measurements; and(c) Test results are difficult or impossible to analyzewhen stray currents are present or direct-connectedgalvanic anodes or foreign impressed current devicesare present and cannot be interrupted.

9.5 Basic Test Equipment

9.5.1 Voltmeter with adequate input impedance.Commonly used digital instruments have a nominalimpedance of 10 megaohms. An analog instrumentwith an internal resistance of 100,000 ohms per voltmay be adequate in certain circumstances in which thecircuit resistance is low. A potentiometer circuit may benecessary in other instances.

9.5.2 Two color-coded meter leads with clips forconnection to the pipeline and reference electrode.

9.5.3 Sufficient current interrupters to interruptinfluential cathodic protection current sourcessimultaneously.

9.5.4 Reference electrode

9.5.4.1 CSE.

9.5.4.2 Other standard reference electrodes maybe substituted for the CSE. These referenceelectrodes are described in Appendix A,Paragraph A2.

9.6 Procedure

9.6.1 Before the test, verify that cathodic protectionequipment has been installed and is operatingproperly. Time should be allowed for the pipelinepotentials to reach polarized values.

9.6.2 Install and place in operation necessaryinterrupter equipment in all significant DC sources

protecting the pipe at the test site, and place inoperation with a synchronized and/or known “off” and“on” cycle. The “off” cycle should be kept as short aspossible but still long enough to read a polarized pipe-to-electrolyte potential after any “spike” as shown inFigure 3a has collapsed.

9.6.3 Determine the location of the site to be tested.Selection of a site may be based on:

(a) Location accessible for future monitoring;(b) Other protection systems, structures, and anodesthat may influence the pipe-to-electrolyte potential;(c) Electrical midpoints between protection devices;(d) Known location of an ineffective coating whenthe pipeline is coated; and(e) Location of a known or suspected corrosiveenvironment.

9.6.4 Make electrical contact between the referenceelectrode and the electrolyte at the test site, directlyover the centerline of the pipeline or as close to it as ispracticable.

9.6.5 Connect voltmeter to the pipeline and referenceelectrode as described in Paragraph 5.6.

9.6.5.1 If spiking may be present, use anappropriate instrument, such as an oscilloscope orhigh-speed recording device, to verify that themeasured values are not influenced by a voltagespike.

9.6.6 Record the pipe-to-electrolyte “on” and “off”potentials and their polarities with respect to thereference electrode.

9.7 Evaluation of Data

Cathodic protection shall be judged adequate at the test siteif the polarized pipe-to-electrolyte potential is negative 850mV, or more negative, with respect to a CSE.

9.8 Monitoring

When the polarized pipe-to-electrolyte potential has beendetermined to equal or exceed a negative 850 mV, thepipeline “on” potential may be used for monitoring unlesssignificant environmental, structural, coating integrity, orcathodic protection system parameters have changed.


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Section 10: Test Method 3—100 mV Cathodic Polarizationof Steel, Cast Iron, Aluminum, and Copper Piping

10.1 Test Method 3 describes the use of either pipelinepolarization decay or pipeline polarization formation todetermine whether cathodic protection is adequate at thetest site according to the criterion. Consequently, this testmethod consists of two mutually independent parts, TestMethods 3a and 3b, that describe the procedures fortesting. Cathodic polarization curves for Test Methods 3aand 3b are shown in Figure 3. These are schematicdrawings of generic polarization decay and formation.

10.2 Test Method 3a — Use of Pipeline Polarization Decay(Figure 3a)

10.2.1 Scope

This method uses pipeline polarization decay to assessthe adequacy of cathodic protection on a steel, castiron, aluminum, or copper pipeline according to thecriterion stated in NACE Standard RP0169,1 Paragraph6.2.2.1.3, 6.2.3.1, or 6.2.4.1 (depending on the pipemetal). The paragraph below states Paragraph6.2.2.1.3:

The following criterion shall apply: A minimum of100 mV of cathodic polarization between thestructure surface and a stable reference electrodecontacting the electrolyte. The formation or decayof polarization can be measured to satisfy thiscriterion.

10.2.2 General

10.2.2.1 Interrupting the known cathodicprotection source(s) eliminates voltage dropsassociated with the protective current(s) beinginterrupted.

10.2.2.2 Other current sources that can affect theaccuracy of this test method include the following:

(a) Unknown, inaccessible, or direct-connectedgalvanic anodes;(b) Cathodic protection systems on associatedpiping or foreign structures;(c) Electric railway systems;(d) HVDC electric power systems;(e) Telluric currents;(f) Galvanic, or bimetallic, cells;(g) DC mining equipment;(h) Parallel coated pipelines, electricallyconnected and polarized to different potentials;(i) Uninterrupted current sources;(j) Unintentional connections to other structuresor bonds to mitigate interference; and(k) Long-line currents.

10.2.2.3 The magnitude and duration of a voltagespike caused by current interruption can vary, butthe duration is typically within 0.5 second. Afterthe current is interrupted, the time elapsed until themeasurement is recorded should be long enoughto avoid errors caused by voltage spiking. On-sitemeasurements with appropriate instruments maybe necessary to determine the duration andmagnitude of the spiking.

10.2.3 Comparison with Other Methods

10.2.3.1 Advantages

(a) This method is especially useful for bare orineffectively coated pipe; and(b) This method is advantageous whencorrosion potentials may be low (for example, 500mV or less negative) and/or the current required tomeet a negative 850 mV polarized potentialcriterion would be considered excessive.

10.2.3.2 Disadvantages

(a) Additional equipment is required;(b) Additional time, personnel, and vehicles maybe required to set up equipment and to make pipe-to-electrolyte potential measurements; and(c) Test results are difficult or impossible toanalyze when direct-connected galvanic anodes orforeign impressed current devices are present andcannot be interrupted, or when stray currents arepresent.

10.2.4 Basic Test Equipment

10.2.4.1 Voltmeter with adequate inputimpedance. Commonly used digital instrumentshave a nominal impedance of 10 megaohms. Ananalog instrument with an internal resistance of100,000 ohms per volt may be adequate in certaincircumstances in which the circuit resistance islow. A potentiometer circuit may be necessary inother instances.

10.2.4.1.1 Recording voltmeters can beuseful to record polarization decay.

10.2.4.2 Two color-coded meter leads with clipsfor connection to the pipeline and referenceelectrode.

10.2.4.3 Sufficient current interrupters to interruptinfluential cathodic protection current sourcessimultaneously.


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Spike

"On" Potential

"Instant Off" Potential (Polarized Potential)

Depolarizing Line

Voltage Drop (IR Drop)

Polarization Decay

Figure 3aPolarization Decay

Normal Operation

"On" Potential

Current Interruption

"Instant-Off"Potential

Polarization

Cathodic Protection Applied

Corrosion Potential

Polarizing Line

Figure 3bPolarization Formation

FIGURE 3Cathodic Polarization Curves

1,200

1,100

1,000

900

800

700

600

500

1,100

1,000

900

800

700

600

500

400

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10.2.4.4 Reference electrode

10.2.4.4.1 CSE.

10.2.4.4.2 Other standard referenceelectrodes may be substituted for the CSE.These reference electrodes are described inAppendix A, Paragraph A2.

10.2.5 Procedure

10.2.5.1 Before the test, verify that cathodicprotection equipment has been installed and isoperating properly. Time should be allowed for thepipeline potentials to reach polarized values.

10.2.5.2 Install and place in operation necessaryinterrupter equipment in all significant DC sourcesprotecting the pipe at the test site, and place inoperation with a synchronized and/or known “off”and “on” cycle. The “off” cycle should be kept asshort as possible but still long enough to read apolarized pipe-to-electrolyte potential after any“spike” as shown in Figure 3a has collapsed.

10.2.5.3 Determine the location of the site to betested. Selection of a site may be based on:

(a) Location accessible for future monitoring;(b) Other protection systems, structures, andanodes that may influence the pipe-to-electrolytepotential;(c) Electrical midpoints between protectiondevices;(d) Known location of an ineffective coating ifthe pipeline is coated; and(e) Location of a known or suspected corrosiveenvironment.

10.2.5.4 Make electrical contact between thereference electrode and the electrolyte at the testsite, directly over the centerline of the pipeline oras close to it as is practicable.

10.2.5.4.1 Identify the location of theelectrode to allow it to be returned to thesame location for subsequent tests.

10.2.5.5 Connect the voltmeter to the pipeline andreference electrode as described in Paragraph5.6.

10.2.5.5.1 If spiking may be present, use anappropriate instrument, such as anoscilloscope or high-speed recording device,to verify that the measured values are notinfluenced by a voltage spike.

10.2.5.6 Measure and record the pipe-to-electrolyte “on” and “instant off” potentials and theirpolarities with respect to the reference electrode.

10.2.5.6.1 The “instant off” pipe-to-electrolytepotential is the “baseline” potential from whichthe polarization decay is calculated.

10.2.5.7 Turn off sufficient cathodic protectioncurrent sources that influence the pipe at the testsite until at least 100 mV cathodic polarizationdecay has been attained.

10.2.5.7.1 Continue to measure and recordthe pipe-to-electrolyte potential until it either:

(a) Has become at least 100 mV lessnegative than the “off” potential; or(b) Has reached a stable depolarized level.

10.2.5.7.2 Measurements shall be made atsufficiently frequent intervals to avoid attainingand remaining at a corrosion potential for anunnecessarily extended period.

10.2.5.7.3 When extended polarizationdecay time periods are anticipated, it may bedesirable to use recording voltmeters todetermine when adequate polarization decayor a corrosion potential has been attained.

10.2.6 Evaluation of Data

Cathodic protection shall be judged adequate at thetest site if 100 mV or more of polarization decay ismeasured with respect to a standard referenceelectrode.

10.2.7 Monitoring

When at least 100 mV or more of polarization decayhas been measured, the pipeline “on” potential at thetest site may be used for monitoring unless significantenvironmental, structural, coating integrity, or cathodicprotection system parameters have changed.

10.3 Test Method 3b—Use of Pipeline PolarizationFormation (Figure 3b)

10.3.1 Scope

This method provides a procedure using the formationof polarization to assess the adequacy of cathodicprotection at a test site on steel, cast iron, aluminum, orcopper piping according to the criteria stated in NACEStandard RP0169,1 Paragraphs 6.2.2.1.3, 6.2.3.1, or6.2.4.1 (depending on the pipe metal). The paragraphbelow states Paragraph 6.2.2.1.3:



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10.3.2 General

Ferrous, aluminum, and copper pipelines may beadequately cathodically protected if applying cathodicprotection causes a polarization change of 100 mV ormore with respect to a reference potential.

10.3.2.1 Current sources that can affect theaccuracy of this test method include the following:

(a) Unknown, inaccessible, or direct-connectedgalvanic anodes;(b) Cathodic protection systems on associatedpiping or foreign structures;(c) Electric railway systems;(d) HVDC electric power systems;(e) Telluric currents;(f) Galvanic, or bimetallic, cells;(g) DC mining equipment;(h) Parallel coated pipelines, electricallyconnected and polarized to different potentials;(i) Uninterrupted current sources;(j) Unintentional connections to other structuresor bonds to mitigate interference; and(k) Long-line currents.

10.3.3 Comparison with Other Methods

10.3.3.1 Advantages

(a) This method is especially useful for bare orineffectively coated pipe; and(b) This method is advantageous whencorrosion potentials may be low (for example, 500mV or less negative) and/or the current required tomeet a negative 850 mV potential criterion wouldbe considered excessive.

10.3.3.2 Disadvantages

(a) Additional equipment is required;(b) Additional time, personnel, and vehicles maybe required to set up equipment and to make thepipe-to-electrolyte potential measurements; and(c) Test results are difficult or impossible toanalyze when stray currents are present or whendirect-connected galvanic anodes or foreignimpressed currents are present and cannot beinterrupted.

10.3.4 Basic Test Equipment

10.3.4.1 Voltmeter with adequate inputimpedance. Commonly used digital instrumentshave a nominal impedance of 10 megaohms. Ananalog instrument with an internal resistance of100,000 ohms per volt may be adequate in certaincircumstances in which the circuit resistance islow. A potentiometer circuit may be necessary inother instances.

10.3.4.2 Two color-coded meter leads with clipsfor connection to the pipeline and referenceelectrode.

10.3.4.3 Sufficient current interrupters to interruptinfluential cathodic protection current sourcessimultaneously.

10.3.4.4 Reference electrode

10.3.4.4.1 CSE.

10.3.4.4.2 Other standard referenceelectrodes may be substituted for the CSE.These reference electrodes are described inAppendix A, Paragraph A2.

10.3.5 Procedure

10.3.5.1 Before the test, verify that cathodicprotection equipment has been installed but is notoperating.

10.3.5.2 Determine the location of the site to betested. Selection of a site may be based on:

(a) Location accessible for future monitoring;(b) Other protection systems, structures, andanodes that may influence the pipe-to-electrolytepotential;(c) Electrical midpoints between protectiondevices;(d) Known location of an ineffective coating ifthe line is coated; and(e) Location of a known or suspected corrosiveenvironment.

10.3.5.3 Make electrical contact between thereference electrode and the electrolyte at the testsite, directly over the centerline of the pipeline oras close to it as is practicable.

10.3.5.3.1 Identify the location of theelectrode to allow it to be returned to thesame location for subsequent tests.

10.3.5.4 Connect the voltmeter to the pipeline andreference electrode as described in Paragraph5.6.

10.3.5.5 Measure and record the pipe-to-electrolyte corrosion potential and its polarity withrespect to the reference electrode.

10.3.5.5.1 This potential is the value fromwhich the polarization formation is calculated.

10.3.5.6 Apply the cathodic protection current.Time should be allowed for the pipeline potentialsto reach polarized values.


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10.3.5.7 Install and place in operation necessaryinterrupter equipment in all significant DC sourcesprotecting the pipe at the test site, and place inoperation with a synchronized and/or known “off”and “on” cycle. The “off” cycle should be kept asshort as possible but still long enough to read apolarized pipe-to-electrolyte potential after any“spike” as shown in Figure 3a has collapsed.

10.3.5.8 Measure and record the pipe-to-electrolyte “on” and “off” potentials and theirpolarities with respect to the reference electrode.The difference between the “off” potential and thecorrosion potential is the amount of polarizationformation.

10.3.5.8.1 If spiking may be present, use anappropriate instrument, such as an

oscilloscope or high-speed recording device,to verify that the measured values are notinfluenced by a voltage spike.

10.3.6 Evaluation of Data

Cathodic protection shall be judged adequate if100 mV or more of polarization formation ismeasured with respect to a standard referenceelectrode.

10.3.7 Monitoring

When at least 100 mV or more of polarizationformation has been measured, the pipeline “on”potential may be used for monitoring unlesssignificant environmental, structural, coatingintegrity, or cathodic protection system parametershave changed.

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References

1. NACE Standard RP0169 (latest revision), “Control ofExternal Corrosion on Underground or Submerged MetallicPiping Systems” (Houston, TX: NACE).

2. NACE Standard RP0177 (latest revision), “Mitigation ofAlternating Current and Lightning Effects on MetallicStructures and Corrosion Control Systems” (Houston, TX:NACE).

3. F.J. Ansuini, J.R. Dimond, “Factors Affecting theAccuracy of Reference Electrodes,” MP 33, 11 (1994), p.14.

4. NACE Publication 35201 (latest revision), “TechnicalReport on the Application and Interpretation of Data fromExternal Coupons Used in the Evaluation of CathodicallyProtected Metallic Structures” (Houston, TX: NACE).

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Bibliography

Ansuini, F.L., and J.R. Dimond. “Factors Affecting theAccuracy of Reference Electrodes.” MP 33, 11 (1994):pp. 14-17.

Applegate, L.M. Cathodic Protection. New York, NY:McGraw-Hill, 1960.

Bushman, J.B., and F.E. Rizzo. “IR Drop in CathodicProtection Measurements.” MP 17, 7 (1978): pp. 9-13.

Cathodic Protection Criteria — A Literature Survey. Ed.coord. R.A. Gummow. Houston, TX: NACE, 1989.

Corrosion Control/System Protection, Book TS-1, GasEngineering and Operating Practices Series. Arlington,VA: American Gas Association, 1986.

Dabkowski, J., and T. Hamilton. “A Review of Instant-OffPolarized Potential Measurement Errors.”CORROSION/93, paper no. 561. Houston, TX: NACE,1993.

Dearing, B.M. “The 100-mV Polarization Criterion.” MP 33,9 (1994): pp. 23-27.

DeBethune, A.J. “Fundamental Concepts of ElectrodePotentials.” Corrosion 9, 10 (1953): pp. 336-344.

Escalante, E., ed. Underground Corrosion, ASTM STP 741.Philadelphia, PA: ASTM, 1981.

Ewing, S.P. “Potential Measurements for DeterminingCathodic Protection Requirements.” Corrosion 7, 12(1951): pp. 410-418.

Gummow, R.A. “Cathodic Protection Potential Criterion forUnderground Steel Structures.” MP 32, 11 (1993): pp.21-30.

Jones, D.A. “Analysis of Cathodic Protection Criteria.”Corrosion 28, 11 (1972): pp. 421-423.

NACE Publication 2C154. “Some Observations onCathodic Protection Potential Criteria in LocalizedPitting.” Houston, TX: NACE, 1954.

NACE Publication 2C157. “Some Observations onCathodic Protection Criteria.” Houston, TX: NACE,1957.


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NACE Publication 35201 (latest revision). “Technical Reporton the Application and Interpretation of Data fromExternal Coupons Used in the Evaluation ofCathodically Protected Metallic Structures.” Houston,TX: NACE, 2001.

NACE Publication 54276. “Cathodic Protection Monitoringfor Buried Pipelines.” Houston, TX: NACE, 1990.

Peabody’s Control of Pipeline Corrosion. 2nd ed. R.Bianchetti, ed. Houston, TX: NACE, 2001.

Parker, M.E. Pipeline Corrosion and Cathodic Protection.2nd ed. Houston, TX: Gulf Publishing, 1962.

Stephens, R.W. “Surface Potential Survey Procedure andInterpretation of Data,” in Proceedings of theAppalachian Corrosion Short Course, held May 1980.Morgantown, WV: University of West Virginia, 1980.

West, L.H. “Fundamental Field Practices Associated withElectrical Measurements,” in Proceedings of theAppalachian Corrosion Short Course, held May 1980.Morgantown, WV: University of West Virginia, 1980.

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Appendix A: Reference Electrodes

A1 Pipeline metals have unstable electrical potentialswhen placed in an electrolyte such as soil or water.However, a half-cell that has a stable, electrochemicallyreversible potential characterized by a single, identifiablehalf-cell reaction is a reference electrode. The stability of areference electrode makes it useful as an electricalreference point or benchmark for measuring the potential ofanother metal in soil or water. When connected by avoltmeter to another metal in soil or water, the referenceelectrode becomes one half of a corrosion cell. Thereference electrodes used for measuring potentials onburied or submerged pipelines have voltage values that arenormally positive with respect to steel.

A2 Pipeline potentials are usually measured using either asaturated copper/copper sulfate (CSE), a silver/silverchloride (Ag/AgCl), or a saturated potassium chloride (KCl)calomel reference electrode. CSEs are usually used formeasurements when the electrolyte is soil or fresh water,and less often for salt water. When a CSE is used in ahigh-chloride environment, the stability (i.e., lack ofcontamination) of the electrode must be determined beforethe readings may be considered valid. Ag/AgCl referenceelectrodes are usually used for seawater environments.The KCl calomel electrodes are more often used forlaboratory work because they are generally less rugged,unless specially constructed, than the other two referenceelectrodes.

A2.1 The voltage equivalents (at 25°C [77°F]) tonegative 850 mV referred to a CSE are:

A2.1.1 Ag/AgCl seawater reference electrodeused in 25 ohm-cm seawater: -800 mV,3 and

A2.1.2 Saturated KCl calomel referenceelectrode: -780 mV.

A2.2 A CSE is composed of a pure copper rodimmersed in a saturated solution of distilled water andcopper sulfate (CuSO4). The pure copper rod extendsfrom one end of the reference electrode, providing ameans of connection to a voltmeter. The other end ofthe reference electrode has a porous plug that is used

to make an electrical contact with the pipelineelectrolyte. Undissolved CuSO4 crystals in thereference electrode should always be visible to ensurethe solution is saturated. The reference is reasonablyaccurate (within 5 mV when measured against areference electrode known to be free of contamination).The advantages of this reference electrode are lowcost and ruggedness.

A2.3 Ag/AgCl reference electrodes are used in marineand soil environments. The construction and theelectrode potential vary with the application and withrelation to the potential of a CSE reference electrode.The electrolytes involved may be natural seawater,saturated KCl, or other concentrations of KCl. Theuser shall utilize the manufacturer’s recommendationsand potential values for the type of Ag/AgCl cell used.The Ag/AgCl reference electrode has a high accuracy(typically less than 2 mV when handled and maintainedcorrectly) and is very durable.

A2.4 A saturated KCl calomel reference electrode forlaboratory use is composed of a platinum wire incontact with a mercury/mercurous chloride mixturecontacting a saturated KCl solution enclosed in a glasscontainer, a voltmeter connection on one end, and aporous plug on the other end for contact with thepipeline electrolyte. For field use a more-rugged,polymer-body, gel-filled KCl calomel electrode isavailable, though modifications may be necessary toincrease contact area with the environment. Thepresence of mercury in this electrode makes itenvironmentally less desirable for field use.

A2.5 In addition to these standard referenceelectrodes, an alternative metallic material or structuremay be used in place of the saturated CSE if thestability of its electrode potential is ensured and if itsvoltage equivalent referred to a CSE is established.

A2.6 A permanently installed reference electrode maybe used; however, whether it is still accurate should bedetermined.


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A3 It is good practice to verify the accuracy of referenceelectrodes used in the field by comparing them with acarefully prepared master reference electrode that, to avoidcontamination, is never used for field measurements. Theaccuracy of a field reference electrode can be verified byplacing it along with the master reference electrode in acommon solution, such as fresh water, and measuring the

voltage difference between the two electrodes. A maximumvoltage difference of 5 mV between a master referenceelectrode and another reference electrode of the same typeis usually satisfactory for pipeline potential measurements.When reference electrode-to-reference electrode potentialmeasurements are made in the field, it is necessary thatelectrodes with matching potentials be used.

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Appendix B: Net Protective Current

B1 NACE Standard RP0169,1 Paragraph 6.2.2.2.1, statesthat measuring the net protective current from theelectrolyte to the pipe surface by an earth current techniqueat predetermined current discharge points may be sufficienton bare or ineffectively coated pipelines when long-linecorrosion activity is of primary concern.

B1.1 This technique is a measure of the net protectivecurrent from the electrolyte onto the pipe surface and ismost practicable for use on bare pipelines.

B1.2 The electrolyte current measurements often arenot meaningful in multiple pipe rights-of-way, high-resistivity electrolyte, deeply buried pipe, large-diameter pipe, stray current areas, and pipe that is notelectrically isolated from other underground structures.Using this technique does not confirm elimination oflocal corrosion cell action.

B2 Measurement Techniques for Net Protective Current

B2.1 The principal anodic areas along the pipelineshould be located. Sufficient cathodic protectioncurrent should be applied to cause a net protectivecurrent from the electrolyte to the pipe surface. Thepipe-to-electrolyte potential measurements for thesetechniques are performed on piping that is notcathodically protected.

B2.2 The two-reference-electrode potential survey ora pipe-to-electrolyte potential survey method is used todetect the probable current discharge (anodic) areasalong a pipeline.

B2.2.1 The two-reference-electrode methodmeasures the direction of the potential gradientalong the earth’s surface. Measurements shouldbe made at 3-m (10-ft) intervals directly over thecenterline of the pipe. The instrument positiveterminal is connected to the lead (front) referenceelectrode in the direction of survey travel. Asuspected anodic condition is indicated by achange of the instrument polarity indication.Suspected anodic conditions and their magnitudescan be confirmed by making two-reference-electrode tests laterally to the pipeline. Onereference electrode is placed over the line and theother spaced laterally the same distance as for thetransverse measurements over the line. These

tests should be made on both sides of the pipe toverify that current is leaving the line.

B2.3 The pipe-to-electrolyte potential survey, whenused as a tool for locating probable anodic conditionson unprotected pipe, should be conducted by makingindividual readings at 3-m (10-ft) intervals along theroute of the pipe. Probable anodic conditions areindicated at survey points where the most negativereadings are determined. It may be desirable toconfirm these suspected anodic conditions by makingthe two-reference-electrode test lateral to the pipe asdescribed for the two-reference-electrode method.

B3 Two-Reference-Electrode Surface Survey

B3.1 Two-reference-electrode surface measurementsconsist of measuring the potential difference betweentwo matched CSEs in contact with the earth. This typeof test, when made directly over the route of the pipe, isuseful in locating suspected anodic conditions on thepipe. The two-reference-electrode survey is particularlysuited for bare pipe surveys to locate anodic areas forapplying a “hot spot” type of protection. The techniqueis not usually used on coated pipe.

B3.2 For this survey technique to be effective, specialattention shall be given to the reference electrodesused. Because potential values to be measured canbe expected to be as low as 1 mV, the referenceelectrodes shall be balanced to within 3 mV of eachother. The potential difference between referenceelectrodes can be measured by:

(a) Placing about 2.5 cm (1 in.) depth of tap water ina small plastic or glass container;(b) Placing the two reference electrodes in the water;and(c) Measuring the potential difference betweenthem.

B3.2.1 If the potential difference between the tworeference electrodes is not satisfactory, they canbe corrected by servicing both referenceelectrodes. This may be accomplished bythoroughly cleaning the inside of the plastic body,rinsing it with distilled water, soaking the porousplug in distilled water or simply replacing the oldplug with a new one, cleaning the copper rod


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inside the reference electrode, and replacing thesolution with new, clean saturated copper sulfatesolution. If the first cleaning does not achieve thedesired results, the process should be repeated.The copper rod should never be cleaned withemery cloth or any other material with metallicabrasive. Only nonmetallic sandpaper should beused.

NOTE: Reference electrode potential values maychange during the survey. Therefore, it isdesirable to check reference electrodesperiodically for balance and to have matched orbalanced spares available for replacement ifneeded.

B3.3 A voltmeter with sufficiently high inputimpedance, at least 10 megaohms, and sufficiently lowranges should be used to make the two-reference-electrode surface survey. Measured values are usuallyless than 50 mV. The required equipment for thissurvey includes an appropriate voltmeter, two balancedCSEs, and related test leads. The front referenceelectrode in the direction of travel shall be connected tothe positive terminal of the instrument. (See FigureB1.)

B3.4 Careful placement of reference electrodes isessential when using the two-reference-electrodesurface survey. Minor measurement errors due toincorrect placement of the reference electrodes canresult in misinterpretation of the data. Before thesurvey is conducted, the pipe should be accuratelylocated and marked, using a dependable locatingdevice. Special care shall be exercised in situations inwhich multiple pipelines are on the same right-of-way.

B3.5 Reference electrode spacing should be uniform.A spacing of 3 m (10 ft) is acceptable. When a groundgradient reversal (anodic condition) has been located,the spacing may be reduced by one half and the areareexamined to locate the anodic area more closely.

B3.6 The survey is made by placing two referenceelectrodes in the earth at the selected spacing directlyover the pipeline. The front test lead in the direction oftravel is connected to the positive terminal of theinstrument. Because the voltage values between thereference electrodes arel normally low, it is desirablethat the reference electrode contact with the earth befree of leaves, grass, rocks, and other debris.

B3.7 Results of the measurement are recorded on anappropriate form. Special attention shall be given torecording the polarity of each voltage measurementcorrectly. With the reference electrodes placed and theinstrument connected as described, a possibly anodiccondition is indicated when a polarity change occurs.(When the polarity of the measured value changesagain, a possibly cathodic condition is indicated.) (SeeFigure B1.)

B3.8 The severity and extent of an anodic conditionmay be further determined by making two-reference-electrode surface measurements lateral to the directionof the pipe. This is accomplished by relocating the rearreference electrode to the side of the pipe. A positivevalue measured from this side reference electrodeindicates current flowing from the pipe into theelectrolyte, which is an anodic condition. A negativevalue measured from this side reference electrodetoward the reference electrode over the pipe indicatescurrent flowing from the electrolyte toward the pipe,which is a cathodic condition. Measurements shouldbe taken on both sides of the pipe. Enoughmeasurements along the pipe and on both sides of thepipe should be taken to define the limits of the anodiccondition.

B3.9 The presence of a galvanic anode connected tothe pipe affects two-reference-electrode surfacemeasurements and generally appears as an anodiccondition. Close observation of measured values quiteoften suggests the presence of galvanic anodes. Asan anode is approached, its presence is usuallyindicated by earth gradients that are somewhat higherthan normal for the area being surveyed. The two-reference-electrode lateral test may provide highermeasured values on the side of the pipe where theanode is buried and lower values on the side of thepipe opposite the anode. Service taps, sideconnections, other components of the pipe (such asmechanical couplings or screw collars with a highermetallic resistance than the pipe), or other close buriedmetallic structures may provide measured values thatindicate an anodic condition. The lateral test is usefulto evaluate the data. Any situation not determined tobe caused by some other factor shall be considered asan anodic condition. Adequate marking of anodicconditions is necessary so they can be located forfuture attention.

B3.10 Soil resistivity tests should be made at anodicareas discovered by using the two-reference-electrodesurface survey. These tests are helpful in evaluatingthe severity of ongoing corrosion, anode current, andanode life.

B3.11 The two-reference-electrode surface potentialsurvey data may be used to generate a pipe-to-electrolyte potential gradient curve using closelyspaced measurements. This curve appears as anyother pipe-to-electrolyte potential curve and isgenerated by the following procedure:

B3.11.1 The pipe-to-electrolyte potential ismeasured at a test point, such as a test station.This value is recorded and becomes the referencevalue to which all other two-reference-electrodemeasurements are referenced.

B3.11.2 The reference electrode is left in the samelocation and is connected to the negative terminalof the voltmeter. A second reference electrode is


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placed over the pipe centerline in clean, moistearth a selected distance from the first referenceelectrode and is connected to the positive side ofthe instrument.

B3.11.3 The potential between the two referenceelectrodes is then measured and recorded.Special attention shall be given to the polarity ofthe measurement between the two referenceelectrodes.

B3.11.4 The measured value is then algebraicallyadded to the pipe-to-electrolyte potentialmeasured in the first step of this procedure. Thesum obtained from the algebraic addition is thepipe-to-electrolyte potential at the location of thesecond reference electrode.B3.11.5 The rear reference electrode (connectedto the instrument negative terminal) is movedforward and placed in the same spot previouslyoccupied by the front reference electrode.

B3.11.6 The front reference electrode is movedahead over the line to the previously selecteddistance.

B3.11.7 The potential between the two referenceelectrodes is again measured with specialattention to reference electrode polarity. Thisvalue is algebraically added to the calculated valuefor the previous test. This calculated pipe-to-electrolyte potential is the pipe-to-electrolytepotential at the location of the front referenceelectrode.

B3.11.8 This process is repeated until the next teststation is met. At this time the last calculated pipe-to-electrolyte potential is compared with the pipe-to-electrolyte potential measured using the teststation. If the survey is carefully performed, uponcomparison these two values should be nearlyidentical.

B3.11.9 These potential data can then be plottedas a typical pipe-to-electrolyte potential curve.

B3.12 Errors in observing instrument polarities,incorrect algebraic calculations, unbalanced referenceelectrodes, and poor earth/reference electrodecontacts cause the calculated values to be incorrect.

B3.13 To use the data collected effectively, a formhaving a suitable format should be developed. Thespecific needs of each user should be consideredwhen a data form is being developed. The form shouldhave space for each measured numerical value, thepolarity of each value, calculated values, andcomments. It is also useful to provide space for asketch of the area surveyed.

B4 Data Interpretation:

B4.1 Interpretation of survey data is complex butshould consider the following:

(a) Polarity change of a measured value;(b) Magnitude of the value measured;(c) Magnitude of the lateral two-reference-electrodevalue;(d) Soil resistivity;(e) Unknown pipe resistances;(f) Physical location of the pipe with respect to otherstructures; and(g) Known corrosion leak history.

B5 Pipe-to-Electrolyte Potential Survey

B5.1 Pipe-to-electrolyte potential measurementsmeasure the potential difference between a CSE incontact with the earth and a connection to the pipeline.When taken and recorded at measurement intervals of3 m (10 ft) directly over a pipeline, thesemeasurements are useful in locating suspected anodicconditions of an unprotected pipeline. The interval ofmeasurement may be shortened when anodicconditions are indicated or other unusual conditionsoccur (see Figures B2a and B2b).

B5.2 Individual users may find it appropriate to modifythe above suggested spacing based on the followingconditions.

(a) Pipeline length;(b) Availability of test leads to the pipe;(c) Terrain characteristics;(d) Accessibility;(e) Presence of foreign pipelines and cathodicprotection systems;(f) Coating condition or lack of coating;(g) Corrosion history of the pipeline;(h) Results of previous surveys; and(i) Pipe depth.

B5.3 The survey consists of measuring and recordingvoltages along an unprotected pipeline at specificintervals as shown in Figures B2a and B2b. Tointerpret the survey data correctly and to ensuremeaningful results, the pipeline must be electricallycontinuous, or the location of insulating or high-resistance joints must be known. The “peaks,” or areasof highest negative potential, usually indicate anodicconditions. Pipe-to-electrolyte potential measurementsshould be plotted or tabulated (see Figure B2c).

B5.4 The presence of an unknown galvanic anodeaffects measurements, causing a location to appear tobe an anodic condition. If records or measurements donot indicate that a galvanic anode has been installed,all “peaks” shall be considered as anodic conditions. Ifrecords regarding galvanic anodes in the area are notavailable or are believed to be inaccurate, a fewadditional measurements can help to determine thesource of the peaks. Pipe-to-electrolyte (or electrode-to-electrode) potential measurements should be made


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in 0.3-m (1-ft) increments for about 1.5 to 3.0 m (5 to10 ft) laterally to the pipe and through the “peak.” Themaximum potential will occur a few feet to the side ofthe pipe if the peak is due to a galvanic anode.Moreover, if the pipe location is known with certaintyand a galvanic anode is present, the potentials will be aminimum over or to the side of the pipe opposite wherethe maximum occurs. The closer the transversemeasurements are to the anode, the more the locationof the minimum will be shifted away from the side of thepipe opposite the location of the maximum.

B5.5 Stray current flowing to a pipe from sources suchas foreign rectifiers and electrified railroads cause thepipe at that location to have more-negative potentialand may be misinterpreted as an anodic condition.Stray current discharging from a pipe can cause a less-negative potential and be misinterpreted as a cathodiccondition.

B6 Cathodic Protection Using the Net Protective CurrentTechnique

B6.1 Cathodic protection should be applied to theanodic area(s).

B6.2 It is necessary to wait until polarization hasstabilized before making a detailed evaluation of thenet current protective level. Polarization of bare pipemay require a relatively long time ranging up to severalmonths.

B6.3 When an impressed current source is used, theside drain potential (potential gradient lateral to thepipe longitudinal direction) should be measured at thepredetermined anodic condition with the protectivecurrent applied. Relative to the reading directly overthe pipe, a higher (more-negative) reading with thereference electrode lateral to the pipe indicates thatcurrent is being conducted to the pipe at this point.The amount of current flow indicated by this methodmay not be enough to control small local corrosioncells.

B6.4 Galvanic anodes are usually installed at or nearthe location of the anodic areas. Caution shall be usedwhen interpreting the results of pipe-to-electrolytepotential measurements made close to an anode.

B6.5 Monitoring of cathodic protection can besimplified by establishing test points and recording thepipe-to-electrolyte potential exhibited when the sidedrain measurements indicate a net current flow to thepipe. These potentials may then be used to monitorthe level of cathodic protection.


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v- - - - -++ + + +

+ xx mV - xx mV- xx mV- xx mV+ xx mV

CURRENT IN PIPE WALL CURRENT IN PIPE WALL

DIRECTION OF SURVEY TRAVEL

CA

TH

OD

IC

AR

EA

AN

OD

ICA

RE

A

CA

TH

OD

IC

AR

EA

Electrolyte

CurrentElectrolyte

Current

UNPROTECTED PIPELINE

v vvv

NOTE: Actual readings are usually 50 mV or less.

As the anodic condition in the center of the figure is passed (traveling left to right), the indicatedpolarity switches from positive to negative. This polarity reversal indicates an anodic condition.

FIGURE B1Surface Potential Survey

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STATIONARY METERAND WIRE REEL

UNPROTECTED PIPE

+_

REFERENCE ELECTRODE POSITIONFOR RELATED READINGS

TEST CONNECTIONTO PIPELINE

NOTE: Cathodic protection not applied.

Figure B2aReference Electrode Intervals for Potential Survey Using Stationary Meter and Wire Reel.

UNPROTECTED PIPE

REFERENCE ELECTRODE POSITIONFOR RELATED READINGSTEST CONNECTION

TO PIPELINE

MOVING METERAND WIRE REEL

+_

Figure B2bReference Electrode Intervals for Potential Survey Using Moving Meter and Wire Reel.

0

100

200

300

400

500

600

700

800

-400

-500

-600

Pip

e-to

-Ele

ctro

lyte

Pot

entia

l(m

V)

AREAS EXPERIENCING CORROSION

-700

CATHODIC PROTECTION NOT APPLIED

Linear Distance

Figure B2cVariation of Pipe-to-Electrolyte Potential with Survey Distance

FIGURE B2Pipe-to-Electrolyte Potential Survey of a Noncathodically Protected Pipeline

Significant errors in the potential measurements can occur when surveys are undertaken as shown if there is abreak in the lead wire insulation or if leakage occurs through the insulation.

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________________________________________________________________________

Appendix C: Using Coupons to Determine Adequacy of Cathodic Protection

C1 Coupons have been used judiciously, particularly whenaccompanied by other engineering tools and data, toevaluate whether cathodic protection at a test site complieswith a given criterion. See NACE Publication 352014 formore information on coupon use. The following testprocedures are suggested as guides.

C2 Cathodic Protection Coupon Test Method 1—forNegative 850 mV Polarized Pipe-to-Electrolyte Potential ofSteel and Cast Iron Piping

C2.1 Scope

This method uses a cathodic protection coupon toassess the adequacy of cathodic protection on a steelor cast iron pipeline according to the criterion stated inNACE Standard RP0169,1 Paragraph 6.2.2.1.2:

A negative polarized potential of at least 850 mVrelative to a saturated copper/copper sulfatereference electrode (CSE).

C2.2 General

C2.2.1 This method uses a coupon to assess theadequacy of cathodic protection applied to aselected test site. A cathodic protection coupon isa metal sample representing the pipeline at thetest site and used for cathodic protection testing.The coupon should be:

(a) Nominally of the same metal and surfacecondition as the pipe;(b) Small to avoid excessive current drain onthe cathodic protection system;(c) Placed at pipe depth in the same backfill asthe pipe;(d) Prepared with all mill scale and foreignmaterials removed from the surface; and(e) Placed at a known location of an ineffectivecoating when the line is coated.

C2.2.2 A coupon has an insulated test leadbrought above ground and, during normaloperations, connected to a pipeline test lead. Thecoupon receives cathodic protection current andrepresents the pipeline at the test site. For testingpurposes, this connection is opened, and thepolarized potential of the coupon is measured.The time the connection is open to measure thecoupon’s “off” potential should be minimized toavoid significant depolarization of the coupon. The“off” period is typically less than 3 seconds. Whenpossible, coupon current direction and magnitudeshould be verified, using a current clip gauge orresistor permanently placed in series with thecoupon lead. Measurements showing discharge

of current from the coupon should be reason toquestion the validity of using a coupon at the testsite.

C2.2.3 The significance of voltage drops due tocurrents from other sources may not be a problemwhen a coupon is used to represent the pipeline.The coupon’s small size may reduce the effect ofthese voltage drops. The magnitude of thesevoltage drops can be quantified by interruptingcathodic protection current sources while thecoupon is disconnected and noting whether thereis a shift in the coupon-to-electrolyte potential.

C2.3 Comparison with Other Methods

C2.3.1 Advantages

(a) Can provide a polarized coupon-to-electrolyte potential, free of voltage drop, with aminimum of specialized equipment, personnel,and vehicles; and(b) Can provide a more comprehensiveevaluation of the polarization at the test site thanconventional pipe-to-electrolyte potentialmeasurements that may be influenced by thelocation, size, and number of coating holidayswhen the pipeline is coated.

C2.3.2 Disadvantage—Can have high initial coststo install coupons, especially for existing pipelines.

C2.4 Basic Test Equipment

C2.4.1 Voltmeter with adequate input impedance.Commonly used digital instruments have anominal impedance of 10 megaohms. An analoginstrument with an internal resistance of 100,000ohms per volt may be adequate in certaincircumstances in which the circuit resistance islow. A potentiometer circuit may be necessary inother instances.

C2.4.2 Two color-coded meter leads with clips forconnection to the coupon and reference electrode.

C2.4.3 Reference electrode

C2.4.3.1 CSE

C2.4.3.2 Other standard referenceelectrodes may be substituted for the CSE.These reference electrodes are described inAppendix A, Paragraph A2.

C2.5 Procedure


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C2.5.1 Before the test, verify that:

(a) Cathodic protection equipment has beeninstalled and is operating properly; and(b) Coupon is in place and connected to apipeline test lead.

Time should be allowed for the pipeline andcoupon potentials to reach polarized values.

C2.5.2 Determine the location of the site to betested. Selection of a site may be based on:

(a) Location accessible for future monitoring;(b) Other protection systems, structures, andanodes that may influence the pipe-to-electrolyteand coupon-to-electrolyte potentials;(c) Electrical midpoints between protectiondevices;(d) Known location of an ineffective coatingwhen the line is coated; and(e) Location of a known or suspected corrosiveenvironment.

C2.5.3 Make electrical contact between thereference electrode and the electrolyte at the testsite as close to the coupon as is practicable.

C2.5.4 Connect the voltmeter to the coupon testlead and reference electrode as described inParagraph 5.6.

C2.5.5 Measure and record the pipeline andcoupon “on” potentials.

C2.5.6 Momentarily disconnect the coupon testlead from the pipeline test lead and immediatelymeasure and record the coupon-to-electrolyte “off”potential and its polarity with respect to thereference electrode. This should be performedquickly to avoid depolarization of the coupon.

C2.5.7 Reconnect the coupon test lead to thepipeline test lead for normal operations.

C2.6 Evaluation of Data

Cathodic protection may be judged adequate at thetest site if the polarized coupon-to-electrolyte potentialis negative 850 mV, or more negative, with respect to aCSE. The polarized potential of the coupon dependson the coupon surface condition, the soil in which thecoupon is placed, its level of polarization, and its timepolarized. Therefore, the polarized potential of thecoupon may not be the same as that of the pipe andmay not accurately reflect the polarization on the pipeat the coupon location. It must also be understood thatthe polarization measured on the pipeline is a“resultant” of the variations of polarization on the pipeat the test site. The causes of these variations includethe pipe surface condition, soil strata variations, oxygendifferentials, and length of time the pipe has been

polarized. Making precise comparisons may not bepossible.

C2.7 Monitoring

When the polarized coupon-to-electrolyte potential hasbeen determined to equal or to exceed a negative 850mV, the pipeline “on” potential may be used formonitoring unless significant environmental, structural,coating integrity, or cathodic protection systemparameters have changed.

C3 Cathodic Protection Coupon Test Method 2—for 100mV Cathodic Polarization of Steel, Cast Iron, Aluminum,and Copper Piping

C3.1 Scope

This method uses cathodic protection couponpolarization decay to assess the adequacy of cathodicprotection on a steel, cast iron, aluminum, or copperpipeline according to the criteria stated in NACEStandard RP0169,1 Paragraphs 6.2.2.1.3, 6.2.3.1, or6.2.4.1 (depending on the pipe metal). The paragraphbelow states Paragraph 6.2.2.1.3:


C3.2 General

Ferrous, aluminum, and copper pipelines may beadequately cathodically protected when applyingcathodic protection causes a polarization change of100 mV or more with respect to a reference potential.

C3.2.1 This method uses a coupon to assess theadequacy of cathodic protection applied at a testsite. A cathodic protection coupon is a metalsample representing the pipeline at the test siteand used for cathodic protection testing. Thecoupon should be:

(a) Nominally of the same metal and surfacecondition as the pipe;(b) Small to avoid excessive current drain onthe cathodic protection system;(c) Placed at pipe depth in the same backfill asthe pipe;(d) Prepared with all mill scale and foreignmaterials removed from the surface; and(e) Placed at a known location of an ineffectivecoating when the line is coated.

C3.2.2 The significance of voltage drops due tocurrents from other sources may be accounted forwhen a coupon is used to represent the pipeline.The magnitude of these voltage drops can be


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quantified by interrupting cathodic protectionsources while the coupon is disconnected andnoting whether there is a shift in the coupon-to-electrolyte potential.

C3.2.3 A coupon has an insulated test leadbrought above ground and, during normaloperations, connected to a pipeline test lead. Thecoupon receives cathodic protection current andrepresents the pipeline at the test site. For testingpurposes, this connection is opened, and thepolarized “off” potential of the coupon is measured.The time the connection is open to measure thecoupon’s “off” potential should be minimized toavoid significant depolarization of the coupon. The“off” period is typically less than 3 seconds. Thecoupon is then allowed to depolarize. Whenpossible, coupon current direction and magnitudeshould be verified, using a current clip gauge orresistor permanently placed in series with thecoupon lead. Measurements showing dischargeof current from the coupon should be reason toquestion the validity of using a coupon at the testsite.

C3.3 Comparison with Other Methods

C3.3.1 Advantages

(a) Can measure coupon-to-electrolyte polari-zation decay with a minimum of specializedequipment, personnel, and vehicles;(b) Can provide an indication of the amount ofpolarization present at the test site withoutinterrupting the cathodic protection currentsupplied to the pipeline;(c) Can provide a better indication of cathodicprotection levels due to eliminating the effects of“long-line” current flow when the pipeline “off”potentials are measured.

C3.3.2 Disadvantage—Can have high initial coststo install a coupon, especially for existingpipelines.

C3.4 Basic Test Equipment

C3.4.1 Voltmeter with adequate input impedance.Commonly used digital instruments have anominal impedance of 10 megaohms. An analoginstrument with an internal resistance of 100,000ohms per volt may be adequate in certaincircumstances where the circuit resistance is low.A potentiometer circuit may be necessary in otherinstances.

C3.4.2 Two color-coded meter leads with clips forconnection to the coupon and reference electrode.

C3.4.3 Reference electrode

C3.4.3.1 CSE.

C3.4.3.2 Other standard referenceelectrodes may be substituted for the CSE.These reference electrodes are described inAppendix A, Paragraph A2.

C3.5 Procedure

C3.5.1 Before the test, verify that:

(a) Cathodic protection equipment is installed(b) and operating properly; and(c) Coupon is in place and connected to apipeline test lead.

Time shall be allowed for the pipeline and couponpotentials to reach polarized values.

C3.5.2 Determine the location of the site to betested. Selection of a site may be based on:

(a) Location accessible for future monitoring;(b) Other protection systems, structures, andanodes that may influence the pipe-to-electrolyteand coupon-to-electrolyte potentials;(c) Electrical midpoints between protectiondevices;(d) Known location of an ineffective coatingwhen the line is coated; and(e) Location of a known or suspected corrosiveenvironment.

C3.5.3 Make electrical contact between thereference electrode and the electrolyte at the testsite as close to the coupon as is practicable.

C3.5.3.1 Identify the location of theelectrode to allow it to be returned to thesame location for subsequent tests.

C3.5.4 Connect the voltmeter to the coupon testlead and reference electrode as described inParagraph 5.6.

C3.5.5 Measure and record the pipeline andcoupon “on” potentials.

C3.5.6 Disconnect the coupon test lead from thepipeline test lead and immediately measure thecoupon-to-electrolyte potential.

C3.5.6.1 The coupon-to-electrolytepotential becomes the “base line value” fromwhich polarization decay is measured.

C3.5.7 Record the coupon-to-electrolyte “off”potential and its polarity with respect to thereference electrode.

C3.5.8 Leave the coupon test lead disconnectedto allow the coupon to depolarize.


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C3.5.9 Measure and record the coupon-to-electrolyte potential periodically. The differencebetween it and the “off” potential is the amount ofpolarization decay. Continue to measure andrecord the coupon-to-electrolyte potential until iteither:

(a) Has become at least 100 mV less negativethan the “off” potential; or(b) Has reached a stable depolarized level.

C3.5.10 Reconnect the coupon test lead to thepipeline test lead for normal operations.

C3.6 Evaluation of Data

Cathodic protection may be judged adequate at thetest site when 100 mV or more of polarization decay ismeasured with respect to a standard reference

28

electrode. The depolarized potential of the coupondepends on the coupon surface condition, the soil inwhich the coupon is placed, its level of polarization,and its time polarized. Therefore, the depolarizedpotential of the coupon may not be the same as that ofthe pipe and may not accurately reflect the polarizationon the pipe at the coupon location. It must also beunderstood that the polarization measured on thepipeline is a “resultant” of the variations of polarizationon the pipe at the test site. These variations arecaused by the pipe surface condition, soil stratavariations, oxygen differentials, and time the pipe hasbeen polarized. Making precise comparisons may notbe possible.

C3.7 Monitoring

When at least 100 mV or more of polarization decayhas been measured, the pipeline “on” potential at thetest site may be used for monitoring unless significantenvironmental, structural, coating integrity, or cathodicprotection system parameters have changed.

NACE International

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