Agenda In class training over PowerPointIn class training over PowerPoint Open discussion and reviewOpen discussion and review LunchLunch Hands on and

AgendaAgenda

• In class training over PowerPointIn class training over PowerPoint

• Open discussion and reviewOpen discussion and review

• LunchLunch

• Hands on and field testingHands on and field testing

• Follow up back in class room settingFollow up back in class room setting

Definition of Stray CurrentDefinition of Stray Current

InterferenceInterference

The National Association of Corrosion The National Association of Corrosion Engineers (NACE) recommended practice on Engineers (NACE) recommended practice on cathodic protection underground structures cathodic protection underground structures

provides several insights to the definition and provides several insights to the definition and evaluation of interference. evaluation of interference.

Stray currentStray current is defined as “current through is defined as “current through paths other than the intended circuit” or “the paths other than the intended circuit” or “the

deterioration of a material, usually a metal that deterioration of a material, usually a metal that results from a reaction with its environment”.results from a reaction with its environment”.

Interference Objectives

Interference Objectives

• RecognizeRecognize

• TestTest

• MitigateMitigate

RecognizeRecognize• Pipe to soil potentials indication of Pipe to soil potentials indication of

possible interference situationpossible interference situation

• Areas of high voltage gradients or Areas of high voltage gradients or polarization polarization

• Structural effect of stray current pickup Structural effect of stray current pickup and dischargeand discharge

TestTest• Basic survey measurements techniques Basic survey measurements techniques

• What are the minimum requirements?What are the minimum requirements?

• Selection of testing equipment and Selection of testing equipment and materialsmaterials

• IR and Polarization measurements IR and Polarization measurements

MitigateMitigate• Why mitigate?Why mitigate?

• Difficulties in interpreting data?Difficulties in interpreting data?

• Selection and method of mitigation Selection and method of mitigation

Fundamental ReviewFundamental Review

• Corrosion diminishes the integrity of the Corrosion diminishes the integrity of the pipeline, increases the probability of pipeline pipeline, increases the probability of pipeline failures and loss of system reliability.failures and loss of system reliability.

• Failure to properly analyze and arrest Failure to properly analyze and arrest corrosion may result in loss of life and corrosion may result in loss of life and property, jeopardize pipeline integrity and property, jeopardize pipeline integrity and corporate image, not to mention the economic corporate image, not to mention the economic forfeiture of pipeline system revenues.forfeiture of pipeline system revenues.

ContinuedContinued

This training session encompasses interference This training session encompasses interference stray current, effect on pipeline polarization, stray current, effect on pipeline polarization, recognition and role of voltage gradients, recognition and role of voltage gradients, importance of the consideration of voltage importance of the consideration of voltage drops, and understanding when stray current drops, and understanding when stray current interference may result in corrosion.interference may result in corrosion.

Fundamental ReviewFundamental Review

Rates of Metal LossRates of Metal Loss

Fe (Iron) / STEELFe (Iron) / STEEL 20LBs /20LBs /AmpAmp/ / YearYear

Al (Aluminum)Al (Aluminum) 6.5 6.5

Cu (Copper)Cu (Copper) 45.7 45.7

Pb (Lead)Pb (Lead) 74.5 74.5

Mg (Magnesium)Mg (Magnesium) 8.8 8.8

Zn (Zinc)Zn (Zinc) 23.6 23.6

Basic Faradays’ LawBasic Faradays’ Law

Given: 1 amp of current discharging from aGiven: 1 amp of current discharging from a

pipeline for 1 year.pipeline for 1 year.

Metal loss: Approximately 20 lbs.Metal loss: Approximately 20 lbs.

EQUIVALENT METAL LOSS

Equivalent Length

Pipe Diameter/W.T. Pipe Weight/Foot of Pipe Loss

4” = 4.500” O.D. x 0.188 W.T 8.66 lbs/ft. 2.31 ft.

6” = 6.625” O.D. x 0.280 W.T. 18.97 lbs/ft. 1.05 ft.

10” = 10.750” O.D. x 0.188 W.T. 21.21 lbs/ft. 0.94 ft.

16” = 16.000” O.D. x 0.250 W.T. 42.05 lbs/ft. 5.70 in.

20” = 20.000” O.D. x 0.250 W.T. 52.73 lbs/ft. 4.55 in.

Stray Current cases can result in high Amp discharges, in which results to rapid corrosion or

metal loss

Remember the basic law of corrosion - For corrosion to occur all the components of a basic corrosion cell must be present.

Conventional Current FlowConventional Current Flow

Cathode AnodeAnode

Positive Negative

Conventional current Flow - is the flow of is the flow of current from positive to current from positive to negative in a electrical negative in a electrical circuit.circuit.

Current Flow - needs to needs to return to it’s original return to it’s original power source.power source.

Electromotive Force is the potential is the potential difference between difference between the two structure.the two structure.

Metallic connection

Electrolyte

Electron Flow

Conventional Current Flow – Conventional Current Flow – Rectified SystemRectified System

Positive (+)

Negative (-)

( - )( - )

Current Flow

Current Flow

Anode bed

Structure - Pipeline

Rectifier Unit

(+)(+)

Recognize Stray CurrentRecognize Stray Current

• Foreign structures nearbyForeign structures nearby– other pipelinesother pipelines– buried tanks or petroleum facilities buried tanks or petroleum facilities

• Increase leakage in areaIncrease leakage in area• Readings increase more negative or positive Readings increase more negative or positive

(Annual monitoring, Bi-monthly inspections)(Annual monitoring, Bi-monthly inspections)• Corrosion focus on a pinpoint location onto Corrosion focus on a pinpoint location onto

structurestructure• Coating disbondment near foreign line Coating disbondment near foreign line

Types of InterferenceTypes of Interference

There are two types of interferenceThere are two types of interference

1.1. DynamicDynamic

2.2. StaticStatic

Dynamic InterferenceDynamic Interference• Dynamic interference is recognized by Dynamic interference is recognized by

pipe-to-soil measurements that fluctuate as pipe-to-soil measurements that fluctuate as a result of the source of stray current. a result of the source of stray current. These currents are continually varying in These currents are continually varying in amplitude and/or continually, changing amplitude and/or continually, changing their electrolytic paths.their electrolytic paths.

• Light rail systems.Light rail systems.• DC mining activities.DC mining activities.• DC welding on the pipeline.DC welding on the pipeline.

Dynamic Interference Example

Two areas of dischargeTwo areas of dischargeTwo areas of dischargeTwo areas of discharge

Bond between pipeline and DC substation

Two Interference bonds Two Interference bonds connectedconnected

Two Interference bonds Two Interference bonds connectedconnected

Reverse Switch or Diodes UsedReverse Switch or Diodes Used

• The rail system potential builds up The rail system potential builds up positivepositive

• In prevention of shorting out company In prevention of shorting out company system with the return interference bond, system with the return interference bond, in which bring the pipe line structure in which bring the pipe line structure positive with the rail system, diodes are positive with the rail system, diodes are used used

Static InterferenceStatic Interference

• Static interference is a steady, continuous Static interference is a steady, continuous stray current source, such as, an impressed stray current source, such as, an impressed cathodic protection rectifier.cathodic protection rectifier.

• This session deals primarily with the This session deals primarily with the definition, recognition, testing, and definition, recognition, testing, and mitigation of static interference stray mitigation of static interference stray current.current.

Static interference caused by a cathodic protection system

Conventional Current FlowConventional Current FlowConventional Current FlowConventional Current Flow

+

-

Current returns Current returns through the soilthrough the soil

Current returns Current returns through the soilthrough the soil

Current Current Discharge Discharge – –

CorrosionCorrosion


CorrosionCorrosion


CorrosionCorrosion


CorrosionCorrosion

Foreign Line Crossing and Stray Current Pickup and Discharge


Current Current Discharge – Discharge –

CorrosionCorrosion


CorrosionCorrosion

Testing non crossing foreign pipeline for stray current interference



CorrosionCorrosion


CorrosionCorrosion


CorrosionCorrosion


CorrosionCorrosion

Voltage GradientsVoltage Gradients

• Remember the rectifier transformers, Remember the rectifier transformers,

– The voltage gradient is build around the primary The voltage gradient is build around the primary coils, energize a iron ore, which the secondary coils coils, energize a iron ore, which the secondary coils picks up the voltage potential and current flows picks up the voltage potential and current flows through the circuitthrough the circuit

– Current still returns backCurrent still returns back

– Stray current works in the same principalStray current works in the same principal

– When ever pipe passes through one of these voltage When ever pipe passes through one of these voltage gradients from a foreign line, it picks up currentgradients from a foreign line, it picks up current

Ion FlowIon Flow

• Remember basic corrosion, electrons Remember basic corrosion, electrons flow the opposite direction as currentflow the opposite direction as current

• At the cathode area (pick up), electrons At the cathode area (pick up), electrons will flow and build up to a negative will flow and build up to a negative potentialpotential

• At the anode area (discharge location), At the anode area (discharge location), loss of electrons builds up to a positive loss of electrons builds up to a positive potentialpotential

Conventional Current FlowConventional Current Flow

• Conventional current will flow, from Conventional current will flow, from positive to negative, positive to negative, – From the foreign ground bed system to the From the foreign ground bed system to the

companies pipeline pickup areacompanies pipeline pickup area– Through the pipeline to the anodeThrough the pipeline to the anode– From the anode (discharge area) to the From the anode (discharge area) to the

foreign structure through the electrolyte foreign structure through the electrolyte

Interference ConsiderationInterference ConsiderationFactors Impacting Corrosion Severity

• Separation and routing of facilities

• The location of the interfering current source

• Magnitude and density of the current

• Coating quality

• Absence of external coating on the structures involved

• Presence and location of mechanical joints of high electrical resistance

Interference DetectionInterference Detection

• When stray current interference is When stray current interference is detecteddetected– Time is of the essenceTime is of the essence– Leakage can occur with in days or weeksLeakage can occur with in days or weeks

TestingTesting

Effect of Interference Stray Current Effect of Interference Stray Current Pickup and DischargePickup and Discharge

Laws of Electricity and Interference Laws of Electricity and Interference CurrentCurrent

• Current will always take the path of Current will always take the path of least resistance.least resistance.

• Stray current will always return to the Stray current will always return to the source. source.

Effect of Interference Stray Current Effect of Interference Stray Current Pickup and DischargePickup and Discharge

Current Discharge May Only Reduce Current Discharge May Only Reduce Polarization.Polarization.

• Where the stray current discharges, a detrimental Where the stray current discharges, a detrimental affect will occur.affect will occur.

• Pipe-to soil readings will be less negative.Pipe-to soil readings will be less negative.

• May result in possible corrosionMay result in possible corrosion

• Whether actual structural damage of corrosion Whether actual structural damage of corrosion occurs depends upon the existing level of occurs depends upon the existing level of cathodic polarization.cathodic polarization.

• If there is adequate polarization, current If there is adequate polarization, current discharge discharge may notmay not cause metal loss. cause metal loss.

• Potential shifts less negative are not necessarily Potential shifts less negative are not necessarily indicative of interference corrosionindicative of interference corrosion

Electronic or IonicElectronic or Ionic

When the stray current discharges, one of When the stray current discharges, one of two reactions will occur.two reactions will occur.

1.1. If adequate polarization exists, the If adequate polarization exists, the current discharge will result in an current discharge will result in an electronic exchange electrochemically.electronic exchange electrochemically.

– No corrosion occurs.No corrosion occurs.– Reduces the cathodic polarization.Reduces the cathodic polarization.

Electronic or IonicElectronic or Ionic

2.2. When there is a lack of cathodic When there is a lack of cathodic polarization present, the discharge of polarization present, the discharge of current will result in corrosion damage.current will result in corrosion damage.

Foreign Stray Current Affect Foreign Stray Current Affect on Polarizationon Polarization

• Stray current pickup increases Stray current pickup increases polarization, this is represented by the polarization, this is represented by the higher,more negative, pipe-to-soil higher,more negative, pipe-to-soil readingsreadings

• Stray current discharge decreases Stray current discharge decreases polarization, this is represented by a polarization, this is represented by a more positive or less negative pipe-to-soil more positive or less negative pipe-to-soil readingsreadings

NativePotential Polarization + IR Drop

Depolarization

1.050 -

1.100 -

.950-

1.300-

(volts)

T = time

In Reference to CSE

.850 - V Polarization Criteria

P/S Reading = .950- V (ON)

Reaching peak Polarization

SufficentCP Polarizatoin300 mV of

@ the peak of Depolarization

.650 -

InterferenceLost350 mVPolarization

Meeting -.850 V Criteria

Total CP being applied = 650 mV

IR drop information needed to use 100 mV shift Criteria or -.850 V polarization criteria

IR drop information needed to use 100 mV shift Criteria or -.850 V polarization criteria

Pick Up and Discharge AreasPick Up and Discharge Areas

• Need to identify areas of Pick up and DischargeNeed to identify areas of Pick up and Discharge– Pick up area, Pick up area,

• More negative More negative

– Discharge area, Discharge area, • More PositiveMore Positive

• Determine locations by CIS Determine locations by CIS – Interrupting foreign structureInterrupting foreign structure

– Data logger is the best tool to useData logger is the best tool to use

Connect Interrupter in Connect Interrupter in series with the structure or series with the structure or ground cable. In this case, ground cable. In this case, we used the structure cable.we used the structure cable.

Interrupter Interrupter MCM used to MCM used to find peak and find peak and valleys of reads.valleys of reads.

Sincorder 2 for Sincorder 2 for the CISthe CIS

Discharge AreaDischarge Area

• Indicated in CIS as the most positive potential Indicated in CIS as the most positive potential readingreading

• The area considered anodicThe area considered anodic• The area that will corrodeThe area that will corrode

– Faraday's law = 1amp = 20lb’s per yrFaraday's law = 1amp = 20lb’s per yr

• Most likely found at the point of crossing or the Most likely found at the point of crossing or the maximum exposure to the foreign linemaximum exposure to the foreign line

• The location for the bond to be establishedThe location for the bond to be established

Graph of Stray Current Pickup and Discharge on Bare Pipeline

Graph of Stray Current Pickup and Discharge on Coated

Pipeline

Pipe-to-Soil Readings Through Foreign Influence and Resultant Depression in Potentials

Rules of Thumb - Interference Rules of Thumb - Interference TestingTesting

1.1. Current will always take the path of Current will always take the path of least resistance.least resistance.

2.2. Current must always return to its Current must always return to its source. source.

3.3. Get the “big picture” of all metallic Get the “big picture” of all metallic structures and possible stray current structures and possible stray current sources, and.sources, and.

Interference Testing Rules of Interference Testing Rules of ThumbThumb

4.4. Follow the data if practical by finding Follow the data if practical by finding the corresponding stray current the corresponding stray current discharge point when a stray current discharge point when a stray current pickup is found.pickup is found.

5.5. Simplest test is to measure the metallic Simplest test is to measure the metallic voltage shiftsvoltage shifts..

The greatest The greatest voltage shiftvoltage shift

The greatest The greatest voltage shiftvoltage shift

Beware of Interference Testing Beware of Interference Testing Difficulties Difficulties

• Limited access to the pipelines due to Limited access to the pipelines due to blacktop or concrete requires drilling to blacktop or concrete requires drilling to obtain measurementsobtain measurements

• Polarization testing is complex and time Polarization testing is complex and time consumingconsuming

• Polarization testing may require Polarization testing may require substantial number of current substantial number of current interrupters that are synchronizableinterrupters that are synchronizable

Beware of Interference Testing Beware of Interference Testing DifficultiesDifficulties

If you have more then one rectifier, you If you have more then one rectifier, you need to have synchronizable current need to have synchronizable current interrupters.interrupters.

Time programmableTime programmable

Master – SlaveMaster – Slave

GPSGPS

Testing CriterionTesting Criterion

• It is necessary prior to conducting any It is necessary prior to conducting any field-testing to gain agreement on what field-testing to gain agreement on what criterion will be utilized to test, evaluate, criterion will be utilized to test, evaluate, interpret, and mitigate any stray current interpret, and mitigate any stray current problems that may be identified. problems that may be identified.

• Prior to conducting field tests all parties Prior to conducting field tests all parties should agree to the standard remediation should agree to the standard remediation requirements. requirements.

Testing CriterionTesting Criterion

• Columbia’s acceptable criteriaColumbia’s acceptable criteria– 50 mV voltage shift, with foreign system 50 mV voltage shift, with foreign system

interrupted, more positive interrupted, more positive – .850- V CSE Criteria, with foreign CP .850- V CSE Criteria, with foreign CP

system operating system operating

• Both criteria's must be metBoth criteria's must be met

Interference Testing Outline Interference Testing Outline SummarySummary

Data Needed to be Obtained:Data Needed to be Obtained:

– A survey of the pipelines with the existing current A survey of the pipelines with the existing current from groundbeds in the area (On Potential Reading from groundbeds in the area (On Potential Reading of the foreign structure)of the foreign structure)

– A survey of each pipelines as if no foreign pipelines A survey of each pipelines as if no foreign pipelines were present with only the companies current (Off were present with only the companies current (Off Potential Reading of foreign structure)Potential Reading of foreign structure)

– A survey of each pipeline depolarized to obtain a A survey of each pipeline depolarized to obtain a static potentialstatic potential


How to Accomplish This?How to Accomplish This?

• Conduct an ON/OFF survey of Columbia’s pipeline with Conduct an ON/OFF survey of Columbia’s pipeline with the existing bonds broken and all known foreign influencing the existing bonds broken and all known foreign influencing rectifiers interrupted (Columbia’s CP system operating) rectifiers interrupted (Columbia’s CP system operating)

• Perform an ON/OFF survey of Columbia’s system with Perform an ON/OFF survey of Columbia’s system with only Columbia’s rectifiers interrupted. The foreign only Columbia’s rectifiers interrupted. The foreign companies are to be turned off at least 12 hours prior to companies are to be turned off at least 12 hours prior to each surveyeach survey

• Obtain potentials after all rectifiers have been turned off Obtain potentials after all rectifiers have been turned off for at least 48 hoursfor at least 48 hours


Why an ON/OFF Survey?Why an ON/OFF Survey?• An ON survey alone does not give insight into the actual An ON survey alone does not give insight into the actual

condition of pipe regarding its actual cathodic protectioncondition of pipe regarding its actual cathodic protection

• The actual cathodic protection is demonstrated by The actual cathodic protection is demonstrated by measuring the chemical activity at the pipeline surface measuring the chemical activity at the pipeline surface that regards corrosionthat regards corrosion

• On potentials have included in the measurementOn potentials have included in the measurement– IR through the soilIR through the soil– IR in the pipeIR in the pipe– Chemical activity representing polarizationChemical activity representing polarization– Native potential of the steelNative potential of the steel


Why an ON/OFF Survey?Why an ON/OFF Survey?ContinuedContinued

• Instant OFF potentials only include the static potential Instant OFF potentials only include the static potential of the steel and the chemical polarization. By of the steel and the chemical polarization. By simultaneously shutting off the current, the IR through simultaneously shutting off the current, the IR through the soil and steel of the pipe is eliminatedthe soil and steel of the pipe is eliminated

• The actual chemical polarization of the pipeline is The actual chemical polarization of the pipeline is determined after static potentials are obtaineddetermined after static potentials are obtained

Instant OFF – Static = chemical PolarizationInstant OFF – Static = chemical Polarization


Determine the Acceptable Amount of Determine the Acceptable Amount of Interference:Interference:

• Must have at least 100 mV of polarization in the “as Must have at least 100 mV of polarization in the “as existing” condition. This results in a protected pipeline existing” condition. This results in a protected pipeline with no metal losswith no metal loss

• Loss of polarization between the individual company Loss of polarization between the individual company does not mean metal loss as long as at least 100 mV of does not mean metal loss as long as at least 100 mV of chemical polarization exists. The companies affected chemical polarization exists. The companies affected must agree upon the acceptable level of polarization must agree upon the acceptable level of polarization loss or gain due to interferenceloss or gain due to interference


Determine the Acceptable Amount of Determine the Acceptable Amount of Interference:Interference:

• If the potentials of the pipeline is above the .850- V If the potentials of the pipeline is above the .850- V CSE criteria with the foreign line CP operating, this CSE criteria with the foreign line CP operating, this indicates adequate polarization on Columbia’s pipeline indicates adequate polarization on Columbia’s pipeline to prevent corrosionto prevent corrosion

• However, due to possible miss-interrupted readings due However, due to possible miss-interrupted readings due to soil conditions with seasonal effects, -50 mV shift is to soil conditions with seasonal effects, -50 mV shift is used as minimum accepted criteria with the foreign used as minimum accepted criteria with the foreign system interrupted system interrupted

• Interrupt the foreign structureInterrupt the foreign structure• Perform CIS over Columbia’s structurePerform CIS over Columbia’s structure• Set interrupter for 500 milliseconds “Off” and 1 Set interrupter for 500 milliseconds “Off” and 1

second “ON”second “ON”• Log survey on data loggerLog survey on data logger• Identify Low points & High points on the “ON” Identify Low points & High points on the “ON”

cyclecycle• Identify & measure Voltage shift to the most Identify & measure Voltage shift to the most

positive direction (maximum exposure area)positive direction (maximum exposure area)• Mark locationsMark locations

Interference Testing Outline Interference Testing Outline Best PracticeBest Practice

Mitigation Mitigation

Mitigation of Stray CurrentMitigation of Stray Current1.1. ““Design and installation of electrical bonds of Design and installation of electrical bonds of

proper resistance between the affected proper resistance between the affected structures.structures.

2.2. Cathodic protection current can be applied to Cathodic protection current can be applied to the affected structure at those locations where the affected structure at those locations where the interfering current is being discharged. The the interfering current is being discharged. The source of cathodic protection may be galvanic or source of cathodic protection may be galvanic or impressed current anodes.impressed current anodes.

3.3. Adjustment of the current output from the Adjustment of the current output from the interfering cathodic protection rectifiers may interfering cathodic protection rectifiers may resolve interference problems.resolve interference problems.

Mitigation of Stray CurrentMitigation of Stray Current4.4. Relocation of the groundbeds of cathodic Relocation of the groundbeds of cathodic

protection rectifiers can reduce or eliminate protection rectifiers can reduce or eliminate the pickup of interference currents on nearby the pickup of interference currents on nearby structures.structures.

5.5. Rerouting of proposed pipelines may avoid Rerouting of proposed pipelines may avoid sources of interference current.sources of interference current.

6.6. Properly located isolating fittings in the Properly located isolating fittings in the affected structures may reduce interference affected structures may reduce interference problems.problems.

7.7. Application of external coating to current Application of external coating to current pickup area(s) may reduce or resolve pickup area(s) may reduce or resolve interference problems.”interference problems.”

• Applying coating to the pick up area, will provide a high resistant barrier for Columbia’s pipeline to pick up current from the foreign ground bed system

Mitigation of Stray CurrentMitigation of Stray Current

Resolution of Interference Resolution of Interference ProblemsProblems

Indications that interference or stray current Indications that interference or stray current problems have been resolved can be problems have been resolved can be demonstrated by:demonstrated by:

• Interrupt system (Foreign structure)Interrupt system (Foreign structure)– 500 milliseconds “ON” and 1 second “Off”500 milliseconds “ON” and 1 second “Off”

• Perform CIS with data loggerPerform CIS with data logger• Indication of no voltage shift or less than 50mVIndication of no voltage shift or less than 50mV• Indication of no potential readings below .850- V Indication of no potential readings below .850- V

CSECSE

Bond at foreign pipeline crossing

Setting a Resistant Bond – Best Setting a Resistant Bond – Best PracticePractice

• Attach two no. 8 and no. 12 wires onto both Attach two no. 8 and no. 12 wires onto both structures (Columbia and foreign structure)structures (Columbia and foreign structure)

• Wire sizes may change due to design of higher Wire sizes may change due to design of higher expected ampere outputexpected ampere output

• Mark the foreign structure wires for easy Mark the foreign structure wires for easy identification (normally with white or red tape)identification (normally with white or red tape)

• Connect an high impedance volt meter to the Connect an high impedance volt meter to the companies no. 12 wire and place the CSE over companies no. 12 wire and place the CSE over the maximum exposure area the maximum exposure area


• Connect an amp meter in series with Columbia Connect an amp meter in series with Columbia and the foreign structure to achieve the maximum and the foreign structure to achieve the maximum current drain readingcurrent drain reading– Set meter at it’s highest setting to prevent blowing fusesSet meter at it’s highest setting to prevent blowing fuses

• Connect a temporary bond rated for the ampere Connect a temporary bond rated for the ampere measuredmeasured

• Normal practice – set up a one ohm slide resister, Normal practice – set up a one ohm slide resister, with the setting half way (= .5 ohms)with the setting half way (= .5 ohms)

• Take potential reading at maximum exposure Take potential reading at maximum exposure area before and after temporary connectedarea before and after temporary connected


• If potential shift over structure goes from If potential shift over structure goes from a depressed state to an impressed state, a depressed state to an impressed state, resistance is too lowresistance is too low

• If potential shift over structure is still in a If potential shift over structure is still in a depressed state, resistance is too highdepressed state, resistance is too high

• Keep adjusting slide resistance to desire Keep adjusting slide resistance to desire criteria is met by checking maximum criteria is met by checking maximum exposure areaexposure area

O N / O FFS W I TC H

A D J US TA B L ER ES I S TO R

# 8 G A G EW I R E TOC O M PA NYL I NE

8 G A G EW I R E TOFO R EI G N L I NE

2 # 1 2 G A G EW I R E TOC O M PA NYL I NE

2 # 1 2 G A G EW I R E TOFO R EI G N L I NE

B O N D B O X

Galvanic anodes used to drain current

Installation of AnodesInstallation of Anodes

• Method is not preferredMethod is not preferred– Due to large amount of current discharge Due to large amount of current discharge

normally consumes anode in rapid time normally consumes anode in rapid time frame, requiring regular replacementframe, requiring regular replacement

– Must connect the anode bed into the test Must connect the anode bed into the test station box for amp drain measurements station box for amp drain measurements

– Decrease in amp drain measurements, may Decrease in amp drain measurements, may indicate depletion of anodesindicate depletion of anodes

– Galvanic anodes used (Magnesium)Galvanic anodes used (Magnesium)

Hydrogen Embrittlement

• Pick area needs to be lowered below –2.00 V CSE due to possible coating disbondment of hydrogen build up and possible hydrogen embrittlement, in which results in pipe failure

• Normal resolution to problem, after bond is set, high potentials exist, add more coating to increase resistance– Bond may need readjusting after completion of task

Shield Installation

• Not preferred,

• Due to cost of excavation with material and labor

• As like the anodes, will deplete over time and need to be replaced

Example 1

• With our rectifier “on” the pipe-to-soil potential for our line is -0.990

• Foreign pipeline has a pipe-to-soil potential of

-0.960

• Rectifier switched “off”• Our potential becomes more positive (-0.850)• Foreign pipeline becomes more negative (-0.980)

O UR G R O UND B ED

O UR R EC TI FI ER

+

_

O UR L I NE

FO R EI G NL I NE

S TA TI O N

Foreign Line Our LineON -0.960 V ON -0.990 VOFF -0.980 V OFF -0.850 V V + 0.020 V V -0.140 V

Conclusion

• Based on the recorded test data, our line is considered to be protected

• The potential on the foreign line decreased(became more positive) when are rectifier was switched on

• There is a possibility a holiday exists near the point of crossing

• The reduction is not sufficient to indicate loss of protection, no corrective measures required

Example 2

• With our rectifier “on” the pipe-to-soil potential for our line is –1.150

• Foreign pipeline has a pipe-to-soil potential of

-0.580

• Rectifier switched “off”• Our potential becomes more positive (-1.040)• Foreign pipeline becomes more negative (-0.880)

O UR G R O UND B ED

O UR R EC TI FI ER

+

_

O UR L I NE

FO R EI G NL I NE

S TA TI O N

F o re ig n L in eO N - 0 .5 8 0O F F - 0 .8 8 0 V + 0 .3 0 0

O u r L in eO N - 1 .1 5 0O F F - 1 .0 4 0 V - 0 .1 1 0

Conclusion

• Based on the recorded test data, our line is considered to be protected

• The potential on the foreign line decreased(became more positive) when are rectifier was switched on

• Need to set a resistance bond to bring the foreign pipeline on potential back to the off potential

DOTDOT

• P/P - P/P -

• DOT Part 192.465 (c)DOT Part 192.465 (c)

Critical Bonds Critical Bonds 6 times each calendar year, not to exceed 2 ½6 times each calendar year, not to exceed 2 ½

months months

Non-Critical BondsNon-Critical Bonds

once each calendar year, not to exceed 15 once each calendar year, not to exceed 15 monthsmonths

DOTDOT

• DOT Part 192.473 (a).DOT Part 192.473 (a).

Each operator whose pipeline system is Each operator whose pipeline system is subjected to stray currents shall have in subjected to stray currents shall have in effect a continuing program to minimize effect a continuing program to minimize the detrimental effects of such currents.the detrimental effects of such currents.

Columbia’s P/P Columbia’s P/P

• Critical bond is where the pipeline is Critical bond is where the pipeline is conducting current through the bond conducting current through the bond and:and:

The bond current is 0.5 Ampere or moreThe bond current is 0.5 Ampere or more

Failure of the bond may result in a potential Failure of the bond may result in a potential change of 100 mV or more below (less change of 100 mV or more below (less negative) the static potential of the pipeline negative) the static potential of the pipeline

Bi-monthlyBi-monthly

• All Critical bonds must be evaluated bi-All Critical bonds must be evaluated bi-monthly or every two months not to monthly or every two months not to exceed 15 daysexceed 15 days

• Pipe to soil reading on company Pipe to soil reading on company structurestructure

Annual MonitoringAnnual Monitoring

• MonitoringMonitoring

Bonds utilizing a diode or reverse current Bonds utilizing a diode or reverse current switch:switch:

A pipe-to-soil potential readingA pipe-to-soil potential reading

Bond current measurementBond current measurement

Test to ensure the blocking device is Test to ensure the blocking device is operative operative

Annual MonitoringAnnual Monitoring

• MonitoringMonitoringAll other bonds:All other bonds:

Pipe-to-soil potential of all structures Pipe-to-soil potential of all structures with the bond connectedwith the bond connectedPipe-to-soil potential of all structures Pipe-to-soil potential of all structures with the bond disconnectedwith the bond disconnectedMeasurement of the bond currentMeasurement of the bond current

Typically five readings obtainedTypically five readings obtained

Slide Resister Slide Resister ApplicationApplication

Slide Resister Slide Resister ApplicationApplication

Resister Wire ApplicationResister Wire ApplicationResister Wire ApplicationResister Wire Application

The amount of Resistance is The amount of Resistance is made by the Length of the made by the Length of the Wire.Wire.

The amount of Resistance is The amount of Resistance is made by the Length of the made by the Length of the Wire.Wire.

Disconnect Bond Wire Disconnect Bond Wire for Amp Drain Readingfor Amp Drain Reading

Disconnect Bond Wire Disconnect Bond Wire for Amp Drain Readingfor Amp Drain Reading

Amp Drain Amp Drain ReadingReading

Amp Drain Amp Drain ReadingReading

Make Make Connection Connection in series in series with the with the CircuitCircuit

Make Make Connection Connection in series in series with the with the CircuitCircuit

1.36 1.36 Amp Amp Current Current DrainDrain

1.36 1.36 Amp Amp Current Current DrainDrain

Slide Slide ResisterResister

Slide Slide ResisterResister

Lighting Lighting ArrestorArrestor

Direct Bond Direct Bond Connection, No Connection, No Resistance Resistance

Direct Bond Direct Bond Connection, No Connection, No Resistance Resistance

Connection Made on Connection Made on Resister from Foreign Resister from Foreign Structure and Structure and Columbia.Columbia.

Connection Made on Connection Made on Resister from Foreign Resister from Foreign Structure and Structure and Columbia.Columbia.

Disconnection to get Amp Disconnection to get Amp Drain must be made in Drain must be made in series with the circuit.series with the circuit.

Shunt ResisterShunt Resister

Measuring Measuring Amp Drain Amp Drain by Measuring by Measuring Voltage Drop Voltage Drop Across the Across the Shunt. Ratio Shunt. Ratio is normally is normally found on found on Shunt. .001Shunt. .001V = 1AV = 1A

7 milivolts = 7 7 milivolts = 7 AmpsAmps

Polarity does Polarity does not matter.not matter.

Make Make connection connection across Shunt.across Shunt.

Ratio for ShuntRatio for Shunt

Shunts do not have to be Shunts do not have to be disconnected in BI-monthly disconnected in BI-monthly and Annual inspection.and Annual inspection.

Basic Corrosion CellBasic Corrosion Cell

1. Anode (more Neg.)

2. Cathode (more Pos.)

3. Metallic connection (pipeline surface, wire, any metal structure)

4. A common electrolyte (water, soil, etc.)

Quick Review -Quick Review -

To provide the driving voltage for current to flow in the corrosion cell, there must be a potential difference between the anode and the cathode.

Take away any one of the four elements in the basic corrosion cell and it will stop the corrosion.

Basic Corrosion CellBasic Corrosion Cell

Role of the EnvironmentRole of the EnvironmentIn the Corrosion Process, the Environment Plays In the Corrosion Process, the Environment Plays

a Major Role.a Major Role.• If soil resistivity is high, current flow is restricted,• Non-uniform environments restrict currents flow at

the transition points,• If moisture is present, the corrosion reaction may

accelerate, • As temperature rises the corrosion rate accelerate,• Other mechanisms, such as, differential aeration and

soil pH will impact how and where the corrosion rates accelerate.

Role of the Environment-pH• An understanding of pH is important in corrosion

and CP work• For many metals, the rate of corrosion increases

appreciably below a pH of about 4• Between 4 and 8 corrosion rate is fairly

independent of pH• Above 8, the environment becomes passive and

the corrosion rate decrease• Cathodic polarization increases the pH at the pipe

surface

Role of the Environment-pH

0 7 14

N eu tra l p H = 7A c id p H < 7

A lka lin e p H > 7

A c id N eutral A lkaline

The pH scale is logarithmic, for each unit of pH the environment become ten times more acid or alkaline

Corrosion Prevention

Coatings.

• Coating is the first line of defense in corrosion prevention.

• Isolating the steel from the environment disrupts the basic corrosion cell.

• Coating damage on the pipeline is called coating holidays.

Figure 2 – Coal Tar Enamel Coating with Area of Coating Removed

Corrosion Prevention

Cathodic Protection.

• Cathodic protection (CP) is a supplement in the prevention of corrosion.

• CP is the application of a DC current.

• The desired effect is to shift the anodic (corrosion) areas on the pipeline to cathodic (protected).

PolarizationPolarization

• Cathodic protection current collects at the coating holidays.

• This DC current forms cathodic “polarization”.• This creates a protective layer at the coating

holiday, when sufficient DC current is available.

• Polarization can be measured by conducting an instant off shift test.

Pipe-to-soil Measurement

Measurement of the CP effectiveness is accomplished by obtaining voltages, which are commonly called “pipe-to-Soil readings”. Readings measure the three components:

1. Chemical activity of the pipe or Polarization

1. Soil or electrolyte voltage (IR) drop

2. Metal voltage (IR) drop

Pipe-to-soil Measurement

• Each component adds voltage to the pipe-to-soil measurement.

• Polarization adds protection to the pipeline.

• Polarization plus native potential most accurately represent the level of CP protection achieved from the CP current.

• Soil and metal voltage drop, add error to the pipe-to-soil readings.

Possible Pipe-to-soil Measurement Errors

• Increases to the pipe-to-soil measurement are a result of current (I) passing through the earth resistance (R).

• Large soil/metallic voltage drop may add significant error to the pipe-to-soil reading.

• Small soil/metallic voltage drop will have a minimal impact.

• P/S reading with the current applied =

[static potential + polarization] + [soil IR + metal IR].

Possible Pipe-to-soil Measurement Errors

Current Interruption to Remove Voltage Drops

• Interrupting the CP sources and measuring the instant off reading removes the IR voltage drops.

• Failure to test for IR voltage drop error can give misleading data and result in misleading conclusions.

• Polarized or Instant Off Potential = [Static Potential + Polarization] + [Soil and Metal I x R = 0]

Recognize Interference

Cathodic Protection Voltage Gradients

• There are two locations that generate voltage gradients:

1. Anodic

1. Cathodic

Typical Anodic Gradient FieldDeveloped By An Isolated Anode

Cathodic Gradient Surrounding Pipeline

Recognize InterferenceRecognize Interference

• Metallic structure picks up stray current from voltage gradients.

-Path of least resistance

• Voltage gradient effect on pipe-to-soil measurements.

-Failure to recognize will result in pipe-to-soil data interpretation error

Foreign Voltage Gradients• When there are anodic voltage gradients present

from foreign cathodic protection systems, data interpretation is more difficult

• Not only are the soil/metal voltage drops present from the company’s CP system, there also from the foreign system

• The presence of these voltage gradients dose not prove that stray current has been picked up or that interference corrosion will be present

Foreign Voltage Gradients

Current pick up is dependent upon:

• Pipeline cathodic polarization

• Coating resistance and quality

• Foreign current driving force

• The earth resistance

• Magnitude of concentration

• Current flow and path of least resistance

Cathodic Protection Criteria

• - 850 mV current applied criterion includes IR drop for pipe-to-soil readings

• 100 mV shift criterion removes the IR drop from the pipe-to-soil readings

Setting A Resistance BondBest Practice

5. Measure the temporary bond current (IT)

between the pipeline and its source of interference and observe its direction.

At the same time, measure the change of the pipe-to-soil potential (ET) caused by the temporary bond current.


6. Measure the resistance (RT) of the temporary bond.

7. Determine the pipe-to-soil voltage change (E1) required to return the pipeline to the original or desired potential from step 2.

8. Use the values (IT), (ET), and (E1) to calculate the current required.


IMAX = IT / ET x E1

IMAX is the current required to correct the stray corrosion at the point of maximum exposure.


RMAX = IT x RT / IMAX

RMAX = maximum resistance of the final drain wire

IT = temporary drain current value in amperes

RT = temporary drain resistance in ohms

IMAX = bond current in amperes required to correct the problem


• Select a cable size of the required length that will give a resistance of a little less that the calculated RMAX.

• The final conditions at the maximum exposure point must be checked after drainage bond is installed to determine if the return potentials are satisfactory.

Documents

Agenda In class training over PowerPointIn class training over PowerPoint Open discussion and reviewOpen discussion and review LunchLunch Hands on and