Water Line Stray Current Control

7/17/2019 Water Line Stray Current Control

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LIGHT RAIL TRANSIT STRAY CURRENT CONTROL:HOW MUCH WATER LINE PROTECTION IS REALLY NEEDED?

Dale Lindemuth, P.E.Corrpro Companies, Inc.

7000B HollisterHouston, Texas 77040

[email protected]

David Kroon, P.E.Corrpro Companies, Inc.

7000B HollisterHouston, Texas 77040

ABSTRACT

Modern-day DC powered light rail lines are designed with many effective stray current controlfeatures built-in, principally an electrically ungrounded traction power negative return circuit.This often includes track construction measures intended to establish much higher track-to-earth resistances when compared to the streetcars of long ago. This attribute dramaticallyreduces stray current leakage to tolerable levels with limited if any negative impact onunderground pipeline corrosion control. Case histories of water pipelines constructed nearlight rail lines built within the last nine years are reviewed. Results of field evaluations inSacramento, Salt Lake City and Minneapolis are presented. Guidelines for stray currentcorrosion protection strategies for ductile iron pipelines are provided.

Keywords: Light rail transit (LRT) line, track-to-earth resistance, ductile iron pipe,polyethylene encasement, cathodic protection, pipe-to-soil potential, track-to-earth potential.

INTRODUCTION

Since the 1970s, most if not all direct current (DC) powered light rail lines constructed in theUnited States have included provisions to control stray traction current directly at the source,i.e. the transit system. Typically, the primary means of minimizing stray current has been tomaximize track-to-earth resistance. All other factors equal, the higher the track-to-earthresistance, the lower the level of stray current and resulting stray current corrosion impact onunderground metallic pipelines and other nearby metallic structures.



For street-running embedded track sections, early attempts to electrically isolate the rails fromground included a poured insulating material immediately around the embedded portion ofeach rail to form an insulated trough. Another approach used an insulating material under theentire track slab. These early rail isolation techniques varied in their effectiveness relative toachieving a suitable design, good workmanship during construction, and long-term durability.

Achieving the target track-to-earth resistance was often a case of hit or miss.

More recent light rail transit (LRT) lines and extensions to existing lines predominantly use anelectrically high resistant “boot” for embedded track sections. The formed boot is fitted aroundeach rail in straight track sections prior to installation of the rail anchors (fasteners) andplacement of the paving. An insulating membrane arrangement (“bathtub”) under and aroundthe entire trackway is often used at crossovers, switches, and other “special track-work” wherethe boot design is not suitable.

Specifications for light rail construction acceptance usually require a minimum track-to-earthresistance after construction is complete. Specified resistances vary from system to systemdepending on expected track-to-earth potentials, utility density, soil resistivity, and severalother design considerations. The authors are aware of specifications for different LRT systems

requiring minimum track-to-earth resistances ranging from 50 ohms-1,000 feet to 250 ohms-1,000 feet for one track (2 rails) for embedded rail construction. As a point of comparison,non-insulated older generation streetcar tracks embedded in asphalt or concrete have track-to-earth resistances in the 0.1 to 1 ohm-1,000 feet range.

Occasionally, realizing the specified minimum track-to-earth resistance has not been an easytask. Extensive troubleshooting and correction of construction deficiencies is sometimesrequired, particularly for the “bathtub” configurations. Unfortunately, for many modern-daytransit lines, once the specified resistance is achieved and the construction is accepted, littleongoing surveillance is performed to determine track-to-earth resistance levels periodicallyduring operation and maintenance. The authors believe periodic track-to-earth resistance

measurements are an important component of transit system O&M procedures. This facilitatesthe reasonable detection and correction of anomalous conditions. It also aids in stray currentcontrol programming as the rail system ages and track-to-earth isolation measures deteriorate.Effective test procedures and troubleshooting techniques readily exist that can be performedwith little if any disruption to transit operations. Remote monitoring through the transit SCADAsystem or other means is also technically viable with a short pay-back period.

This paper presents three case histories where ductile iron water pipelines were included inthe construction of light rail lines built within the last nine years. The pipelines were installedunder and parallel to the LRT lines, typically as a relocation of an existing pipeline because ofa conflict with the transit construction. The primary stray current control and monitoring design

for the pipelines consisted of pipe joint electrical bonding, test stations and polyethyleneencasement (ANSI/AWWA C105/A21.51). Cathodic protection using either galvanic anodes oran impressed current system was not included.

The LRT tracks in the immediate vicinity of all three case histories are embedded in the street.The rails are designed to have a high track-to-earth resistance. The insulating rail boot is usedin all cases for straight track sections.



The data from the ductile iron pipeline case histories document the stray current corrosioncontrol performance of the particular mitigation measures employed. They also aid indeveloping stray current corrosion protection design guidelines for new ductile iron pipelinesconstructed near light rail transit lines where positive track-to-earth isolation measures areincluded.

FIELD EVALUATION PROCEDURES

Battery-powered portable digital dataloggers captured most of the field data. This includedpipe-to-soil potential measurements and pipe current measurements at test stations. Pipecurrent measurements used a span of pipe as a calibrated shunt, either a 100-feet long spanwith test wires brought into a common test station or by measuring the voltage drop across aspan of pipe between two consecutive test stations. Monitoring periods typically ranged fromone hour to one day depending on location and initial observations.

Where allowed by the transit operator, track-to-earth potential measurements documented thisparameter and related it to stray current effects detected on the ductile iron pipelines. In thecase of the Sacramento and Minneapolis evaluations, the track-to-earth resistance for thesection of LRT line in the immediate vicinity of the study area was determined.

CASE HISTORIES – SACRAMENTO, SALT LAKE CITY, AND MINNEAPOLIS

Case History No. 1 - Sacramento, California

Operations for the Sacramento “RT” light rail transit system commenced in 1987 with an 18-mile “starter line.” Since then, additional lines and extensions have been built, the most recentbeing an extension of the Gold Line into the downtown central business district in late 2006.The total length of the light rail system is currently 37 miles.

As part of the Gold Line extension, a 1,300-feet long section of paralleling 20-inch diameter

and 24-inch diameter riveted steel water pipelines was replaced with a single 42-inch diameterductile iron main. The riveted steel pipelines were installed in 1873 and 1903 respectively.The new ductile iron pipeline crosses under the LRT tracks at two locations. It then extends inthe street perpendicular to the rail line for 800 feet. Figure 1 shows the basic arrangement.The pipeline crosses the LRT at 7th and 8th Streets.

The new ductile iron pipeline design included polyethylene encasement, pipe joint bonding,test stations, and pipe insulating flanges at tie-ins. At the onset of construction in 2005, thepipeline contractor was trained on the proper installation of these materials. Due diligence bythe contractor and by the inspectors resulted in the quality installation needed for effectivestray current corrosion control. Figures 2 through 4 show photographs of the pipe

construction.

Figures 5 and 6 present sample datalogger traces (versus time) for two of the pipe-to-soilpotential measurements. Figure 7 shows pipe current flow (2 locations) and Figure 8 shows atrace of the track-to-earth potential. Pipe-to-soil potential measurements were made at thecrossings with the LRT and at the end test station 800 feet perpendicular from the LRT line.These locations typically would be expected to experience the maximum variations(fluctuations) in pipe-to-soil potential because of transit operations, which the collected data



demonstrates. The pipe current measurements were taken at intermediate locations wherestray current flow along the pipeline is usually the greatest.

The polarity used for the pipe-to-soil potential dataloggers for each case history was such thata positive potential change on the traces (with respect to absolute zero) indicates possiblestray current corrosion (anodic effects). A negative potential change indicates the transit-generated stray current may be reducing pipe corrosion rates during the particular event(cathodic effects).

The magnitude-time relationship for the potential and current measurements in Figures 5through 7 are characteristic of a pipeline being influenced by a DC powered transit line. Thesepatterns are similar to those for the LRT track-to-earth potentials (Figure 8), indicating adefinite cause and effect relationship. Track-to-earth potentials typically vary throughout theday with a predictable signature as traction power demands fluctuate. The fluctuations areeffected by transit vehicle acceleration and deceleration, and the number and location ofvehicles on the system, among other influencing factors. The track-to-earth potentialvariations and the resulting stray current effects on nearby structures are caused by thecombined operation of transit vehicles along the entire rail system, not just the vehiclesoperating in the immediate vicinity. The track-to-earth potentials represent a portion of the

total voltage drop developed in the running rails because of propulsion current through the railsbetween the transit vehicles and the traction power substations.

As shown in Figures 5 and 6, maximum corrosive or protective variations are in the 0.03 to0.05 volt range. Pipe current (Figure 7) is bi-directional with a typical maximum variation ineither direction of approximately 0.05 to 0.10 ampere. When analyzing transit generated straycurrent effects on a pipeline or other structure, it is important to recognize that an individualpeak effect (e.g. potential or current) has a very short time duration. This is illustrated by theexpanded trace in Figure 9 that shows a 5-minute portion of the same pipe-to-soil potentialrecording in Figure 5. Any given positive or negative peak in pipe-to-soil potential lasts lessthan 10 seconds.

To better assess the stray current corrosion impact on pipelines, time weighted average valuesof pipe-to-soil potential and pipe current are calculated. The time weighted average valuesallow the dynamic (time varying) conditions to be related to interference effects caused by aconstant source of stray current, e.g., an impressed current cathodic protection system. Thehorizontal lines in the potential and current traces in Figures 5 through 7 and 9 show the timeweighted values. This is also true for the data discussed later for the Salt Lake City andMinneapolis case histories.

For the Sacramento ductile iron pipeline, the following time weighted average interferenceeffects are calculated:

Pipe-to-soil potential change, corrosive or protective – no more than 0.007 volt. Pipe current – less than 0.015 ampere with the predominant direction westward away

from the LRT.

While the evaluation of the Sacramento water pipeline shows the LRT is causing stray currentinterference, the magnitude and time varying nature of this interference is inconsequential topipe service life, provided there is no significant increase. Time weighted average variations in



pipe-to-soil potential would typically have to exceed 0.05 to 0.10 volt before raising a concernrelative to long-term pipe reliability. In such cases, further field investigation would beappropriate to determine the corrosion control significance of the measured effects.

It is worth noting that a very low track-to-earth resistance, less than 1 ohm-1,000 feet, wasmeasured during the field testing for an approximate 1,000 feet long section of the LRT railsnear the two crossings with the water pipeline. These data were obtained during the earlymorning hours when LRT vehicles pass through the area on a reduced schedule. The

minimum track-to-earth resistance for construction acceptance for the Sacramento RT (GoldLine Extension) is 200 ohms-1,000 feet for embedded rails. Troubleshooting has beenundertaken subsequent to the water line evaluation to determine the cause of the out-of-specification condition and establish a suitable course of action. For the particular waterpipeline evaluated, the insignificant stray current influences will be reduced even further oncecorrective action is taken. The very low-level stray current effects on the water linedemonstrate the value of the selected stray current control measures, even under extreme,anomalous conditions.

Case History No. 2 – Salt Lake City, Utah

With the first phase opening for revenue service in 1999, the current total length of the TRAXlight rail system in Salt Lake City is 23 miles. Major sections of the TRAX rails are embeddedin the street. The construction specifications included a minimum track-to-earth resistance of250 ohms-1,000 feet for acceptance of the embedded track.

Ductile iron water piping totaling over five miles was included in the TRAX construction. Thestray current corrosion control system of choice for much of the piping along the Sandy/SaltLake LRT line consisted of polyethylene encasement, pipe joint bonding and test stations. TheSandy/Salt Lake line has been in service since 1999. The data discussed here was obtainedin October 2006, seven years after construction.

The pipe-to-soil potential traces in Figures 10 through 12 typify conditions along thepolyethylene encased and electrically continuous sections of ductile iron pipe that parallel andcross straight track construction where the insulating rail boot was used. Pipeline test stationsfor these measurements as well as other measurements in Salt Lake City are all within 50 feetof the LRT tracks, often within 20 feet. The transit generated fluctuations vary from virtuallynon-existent (Figure 10) to no more than a time weighted average of 0.01 volt (Figure 12).Pipe current measured at one location (Figure 12) exhibited a total variation of 0.38 ampere.The equivalent time weighted average current is 0.06 ampere. Similar to Sacramento (CaseHistory No. 1), the very low-level stray current effects are of little corrosion consequence,provided there is no significant increase.

Figures 13 and 14 present pipe-to-soil potential traces near switch tracks that use an insulating“bathtub” arrangement to increase track-to-earth resistance. While still considered tolerable,the pipe-to-earth potential variations at these locations are notably greater than thosemeasured along the straight track sections (Figures 10 through 12). The maximum variationsoccur near an embedded “T” track where the Sandy/Salt Lake LRT line connects to theUniversity Line. In this case, time weighted average corrosive and protective variations inpipe-to-soil potentials of 0.034 volt and 0.042 volt are calculated respectively (Figure 14). Arecords review indicates this condition was first detected in 2002. Experience suggests the



cause of the increased stray current effects is likely related to a less than desired track-to-earthresistance for the special “T” track construction. It is quite possible the condition existed sincethe “T” track was constructed in 2001. This points out the need for adequate track-to-earthresistance testing during the construction phase to correct deficiencies before transit servicebegins.

Figure 15 shows a pipe-to-soil potential trace for a ductile iron water main along the TRAXUniversity Line. This pipeline was constructed in 2001 and included a bonded dielectric

coating, pipe joint bonding, and test stations. Transit caused corrosive and protectivevariations in pipe-to-soil potential are 0.011 and 0.014 volt respectively. At face value, there isno discernible difference in stray current corrosion control performance when compared to thepolyethylene encased ductile iron pipelines discussed elsewhere in this paper. The primarydifference is the notably greater cost for the dielectric coating. Work by Kroon (Kroon, 20052)indicates the dielectric coating typically represents a capital and life cycle cost increase ofmore than 10% when compared to the pipe alone without corrosion control. In contrast, theincreased cost associated with polyethylene encasement is less than two percent.

Case History No. 3 – Bloomington, Minnesota (suburb of Minneapolis)

Opened for service in 2004, the Hiawatha light rail line in the greater Minneapolis area is 12miles long. It provides service between downtown Minneapolis, the Minneapolis/St. PaulInternational Airport, and the Mall of America in Bloomington. A minimum track-to-earthresistance of 200 ohms-1,000 feet was specified for construction acceptance of the embeddedtrack. A review of the construction records indicates excellent (high) resistances at that timefor embedded track, typically in the 500 to 1,000 ohms-1,000 feet range. A track-to-earthresistance in excess of 600 ohms-1,000 feet was measured for a 1,700-feet long section ofLRT system in the immediate area of the pipeline measurements

The predominantly ductile iron water pipeline system included in this case history is operatedby the Bloomington Utilities Department. The piping evaluated parallels and crosses

embedded track near the Mall of America. Pipe construction along the LRT in Bloomingtonincluded polyethylene encasement, pipe joint bonding, and test stations for stray currentcontrol and monitoring. The Bloomington Utilities Department standard of construction forductile iron pipe outside the transit corridor includes pipe joint bonding for electrical thawing ofservice laterals during the very cold winter months.

Figures 16 through 18 present potential and current traces for three locations included in thiscase history. Figure 16 shows the pipe-to-soil potential traces at the three locations. Alsoshown in this figure is a power neutral (electrical ground) to soil potential trace at Location No.3. Figure 17 is a trace of pipe current. Figure 18 shows the track-to-earth potentialmeasurements.

Once again, the pipe-to-earth potential data and the pipe current data indicate stray currentsfrom transit operations have inconsequential effects on pipe corrosion rates. ReferencingFigure 16, corrosive and protective pipe-to-soil potential fluctuations are both typically lessthan 0.01 volt. The limited monitoring period precludes an accurate calculation of the timeweighted average potential changes. As shown in Figure 17, measured variations in pipecurrent are generally less than 0.2 ampere with a time weighted average value of 0.048ampere.



Track-to-earth potentials (Figure 18) vary between +20 volts (stray current discharging fromthe rails) and -20 volts (stray current accumulating on to the rails). The magnitude and bi-polarity nature of the track-to-earth potentials are typical of an LRT system and do not indicateany readily apparent operational irregularities.

Referencing Figure 16, the power neutral-to-soil potential trace (“Loc. 2PN Power Neutral”)exhibits variations that are five times greater than the corresponding pipe-to-earth potential

variations at the same location (“Loc. 2 Pipe”). Typically, power neutral connections are moresensitive to stray current influences as they represent a composite of effects because of theextensive, distributed electrical neutral/grounding system. As such, power neutral-to-soilpotential measurements often provide a good “first glance” assessment of stray current effectson the underground infrastructure.

The exemplary, inconsequential stray current impact on the Bloomington water lines isconsistent with satisfactory findings reported for the natural gas distribution system in the area(Beggs and Fitzgerald 20053). The effective control of transit generated stray current isattributed to proactive design and construction efforts for the transit system and for theunderground utilities. The gas company continues to monitor their facilities for stray current.

This includes permanent, buried clamp-on ammeters placed around the pipe at strategiclocations. Instrument wires from the ammeter clamps are routed to test stations used forperiodic surveillance and connected to a portable meter when measurements are made.

CONCLUSIONS

1. Stray currents emanating from DC powered light rail lines can be effectively minimized toinconsequential levels by establishing and maintaining a high track-to-earth resistance,which is practical to achieve. Track designs should be based on in-service conditionsexpected over the life of the rail system, including the effects of moisture accumulating onthe track surface during rain events, snowstorms, etc.

2. The three case histories discussed in this paper demonstrate the effective use ofpolyethylene encasement and pipe joint bonding for controlling and monitoring transitgenerated stray current corrosion on underground ductile iron pipelines. These findings areconsistent with water line evaluations by others for the LRT in Portland, Oregon(Greenberger 20054).

3. Data obtained in Salt Lake City indicate no discernible difference in the stray currentcorrosion control performance of polyethylene encased ductile iron pipe when compared toductile iron pipe installed with a notably more expensive bonded dielectric coating.

4. Stray current corrosion control measures for ductile iron pipelines should be determinedbased on project specific considerations. This includes the anticipated levels of straycurrent leakage from the transit system over the desired life of the pipeline, O&Mprocedures and commitment, and soil corrosivity. A holistic approach is best when definingcost effective corrosion control measures, taking into account stray current impacts andnatural, galvanic corrosion rates.



5. For modern-day LRT systems that employ an effective means of isolating the rails from

ground, the minimum corrosion protection measure for ductile iron pipe should bepolyethylene encasement. Project specifications and inspection practices shouldadequately cover this item to avoid out-of-specification materials and assure a qualityinstallation.

6. Pipe joint bonding of polyethylene encased ductile iron pipe allows for stray current

monitoring, if deemed appropriate by the designer and pipeline operator. Cathodicprotection further reduces pipe corrosion rates and is completely compatible withpolyethylene encasement. The synergistic use of these two corrosion control strategies iswell proven based on several years of experience in highly corrosive soils (Lindemuth andKroon 20075, Horton et al 20056, Bell and Romer 20047).

7. While polyethylene encasement, with or without pipe joint bonding and cathodic protection,is the stray current corrosion control method of choice for ductile iron pipelines near newLRT lines, it may not be appropriate in all cases. This is particularly true when high levelsof stray earth currents exist or can be expected, e.g. older streetcar systems such as thosein Philadelphia and Boston. Again, stray current corrosion control measures should be

determined based on project specific considerations and analyses.

8. Utility operators should play an active role in the planning and design stages of new LRTsystems to assure adequate provisions are included in the construction to maintain straycurrent levels to a practicable minimum. Master agreements between the utilities and thetransit agencies should include appropriate language to protect the utility infrastructure fromtransit generated stray current over the life of the rail system. Utility operators should be anintegral part of the transit system design review process, including having stray currentcorrosion control input for relocated utility facilities.

9. Once an LRT system begins service, utility operators should be cognizant of the need for

some reasonable level of stray current control surveillance. The extent of this surveillancedepends heavily on the in-service level of track-to-earth resistance maintained by thetransit agency.

ACKNOWLEDGEMENTS

The authors wish to acknowledge the following agencies for their wholehearted support of andparticipation in the stray current corrosion control evaluations summarized herein:

City of Sacramento Department of Utilities Sacramento Regional Transit District Salt Lake City Public Utilities Utah Transit Authority (TRAX) City of Bloomington Utilities Metro Transit, Minneapolis/St. Paul Metro Area



REFERENCES

1. American Water Works Association. “Polyethylene Encasement for Ductile Iron PipeSystems”, ANSI/AWWA C105/A21.5, AWWA, Denver CO

2. D. Kroon. “Life Cycle Cost Comparisons of Corrosion Protection Methods for Ductile IronPipe”. CORROSION 2005, paper no. 05037. (Houston, TX: NACE International, 2005)

3. J. Beggs, J. Fitzgerald. “Stray Current Testing on Gas Distribution Piping Following Start-Up of a New Light Rail Transit Line”. CORROSION 2005, paper no. 05248. (Houston, TX:NACE International, 2005)

4. S. Greenberger. “Parametric Stray Current Monitoring and Mitigation for Electric Rail StrayCurrent”. CORROSION 2005, paper no. 05249. (Houston, TX: NACE International, 2005)

5. D. Lindemuth, D. Kroon. “Cathodic Protection of Pipe Encapsulated in Polyethylene Film”.CORROSION 2007, paper no. 07040. (Nashville, TN: NACE International, 2007)

6. M. Horton, D. Lindemuth, G. Ash. “Ductile Iron Pipe Case Study: Corrosion ControlPerformance Monitoring In A Severely Corrosive Tidal Muck”. CORROSION 2005, paperno. 05038. (Houston, TX: NACE International, 2005)

7. G. Bell, A. Romer. “Making “Baggies” Work for Ductile Iron Pipe”. ASCE Pipelines-2004Conference, American Society of Civil Engineers, Reston VA

FIGURE 1 – Sacramento Water Main Layout



FIGURE 2 – Sacramento Water Main Construction – 42” Diameter Ductile Iron



FIGURE 3 – Sacramento Water Main Construction, Pipe Joint Bonding

FIGURE 4 – Sacramento Water Main ConstructionProper Materials For and Installation of Polyethylene Encasement is a Must!



-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

3:00 PM 6:00 PM 9:00 PM 12:00 AM 3:00 AM 6:00 AM 9:00 AM

P I P E T O

S O I L P O T E N T I A L

C H A N G E ( V O L T )

8th Street at Transit Line 21+00

Time Weighted Corrosive (+) Potent ial Change +0.003 Volt

Time Weighted Pro tecti ve (-) Potential Change -0.003 Volt

FIGURE 5 – Sacramento Water Main Potential, 8th Street at Transit Line

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

12:00 AM 3:00 AM 6:00 AM 9:00 AM 12:00 PM 3:00 PM 6:00 PM

P I P

E T O

S O I L P O T E N T I A L C H A N G

E ( V O L T )

5th Street 10+00

Time Weighted Corrosive (+) Potential Change +0.007 Volt

Time Weighted Protective (-) Potential Change -0.005 Volt

FIGURE 6 – Sacramento Water Main Potential, 5 th Street



-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

3:00 PM 9:00 PM 3:00 AM 9:00 AM 3:00 PM 9:00 PM 3:00 AM

P I P E C U R R E N T ( A

M P E R E )

6th Street 13+00

7th Street at Transit L ine 18+00

Time Weighted Average (+) Current Westward +0.014 Ampere

Time Weighted Average (-) Current Eastward -0.012 Ampere

6th Street7th Street

FIGURE 7 – Sacramento Water Main Current

-8

-6

-4

-2

0

2

4

6

8

10:00 AM 10:30 AM 11:00 AM 11:30 AM 12:00 PM 12:30 PM

T R A C K T O

E A R T H P O T E N T I A

L ( V O L T )

8th Street Transit Rails 21+00

Connection to rail temporarily

removed to allow LRT to pass (typ.)

FIGURE 8 – Sacramento Track-to-Earth Potential



-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

5:05 PM 5:06 PM 5:07 PM 5:08 PM 5:09 PM 5:10 PM

P I P E T O

S O I L P O T E N T I A L C H

A N G E ( V O L T )

8th Street at Transit Line 21+00

Time Weighted Corrosive (+) Potential Change +0.003 Volt

Time Weighted Protective (-) Potential Change -0.003 Volt

FIGURE 9 – Sacramento Water Main Potential, 8th Street at Transit Line (Zoom)

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

11:00 AM 1:00 PM 3:00 PM 5:00 PM

P I P E T

O

S O I L P O T E N T I A L V A R I A T I O N ( V O

L T )

S. Temple at W. Temple, At Downtown End Of TRAX

FIGURE 10 – Salt Lake City Water Main Potential, South Temple



-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

10:00 AM 12:00 PM 2:00 PM 4:00 PM

P I P E

T O

S O I L P O T E N T I A L V A R I A T I O N ( V O L T )

Main at 100S, Parallel To TRAX

Time Weighted Average Corrosive (+) Potential Variation +0.003 Volt

Time Weighted Average Protective (-) Potential Variation -0.003 Volt

FIGURE 11 – Salt Lake City Water Main Potential, Main at 100S

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

1:00 PM 2:00 PM 3:00 PM 4:00 PM 5:00 PM

P I P E T O

S O I L P O T E N T I A L V A R I A T I O N ( V O L

T )

200W at Fayette Avenue, Parallel to TRAX Sandy Line



Time Weighted Average Variation In Pipe Current = 0.06 Ampere (0.38 Ampere Peak)

FIGURE 12 – Salt Lake City Water Main Potential, 200W at Fayette Avenue



-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

9:00 AM 12:00 PM 3:00 PM 6:00 PM 9:00 PM 12:00 AM

P I P E T O

S O I L P O T E N T I A L V A R I A T I O N ( V O L T )

200W at 700S, Parallel to TRAX Sandy Line



FIGURE 13 – Salt Lake City Water Main Potential, 200W at 700S

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

9:00 AM 11:00 AM 1:00 PM 3:00 PM 5:00 PM

P I P

E T O

S O I L P O T E N T I A L V A R I A T I O N

( V O L T )

Main at Universi ty (400S), at TRAX Switch Track, Northeast Corner



FIGURE 14 – Salt Lake City Water Main Potential, Main at Universi ty



-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

3:00 PM 9:00 PM 3:00 AM 9:00 AM

P I P E

T O

S O I L P O T E N T I A L V A R I A T I O N ( V

O L T )

University Blvd. at 1100E, Parallel to TRAX University Line



FIGURE 15 – Salt Lake City Water Main Potential, University Blvd. (Dielectric Coating)

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

6:00 AM 9:00 AM 12:00 PM 3:00 PM 6:00 PM

P I P E

T O S O I L P O T E N T I A L V A R I A T I O N ( V O L

T )

LOC. 1 - Crossin g LRT Near Mall of America - Pipe

LOC. 2 - Crossing L RT at American Boulevard - Pipe

LOC. 3 - Paralleling L RT at I-494 - Pipe

LOC. 2PN - American Bou levard - Power Neutral

LOC. 1

Pipe

LOC. 2

Pipe

LOC. 3

Pipe

LOC. 2PN

Power

Neutral

FIGURE 16 – Bloomington Water Main Potentials



0.00

0.10

0.20

0.30

10:30 AM 10:35 AM 10:40 AM 10:45 AM 10:50 AM 10:55 AM 11:00 AM

P I P E C U R R E N T ( A M P

E R E )

LOC. 3 - Paralleling LRT at I-494

Time Weighted Average Current +0.048 Ampere

FIGURE 17 – Bloomington Water Main Current

-20

-15

-10

-5

0

5

10

15

20

3:30 PM 4:30 PM 5:30 PM

R A I L T O E A R T H P O T E N T I A L ( V O

L T )

LOC. 3 - At I-494

LOC. 1 - Near Mall of Am erica

LOC. 3

Rail

LOC. 1

Rail

FIGURE 18 – Bloomington Track-to-Earth Potent ial

Documents

Water Line Stray Current Control