Stray Current Corrosion Control For DC Rail Transit Systems Stray Current Western... · Stray Current Corrosion Control ... Corrosion = Current x Time ... “Bi-Polar Stray Currents”

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Stray Current Corrosion ControlStray Current Corrosion ControlFor DC Rail Transit SystemsFor DC Rail Transit Systems

Dale Lindemuth, P.E.Director of Engineering

Houston, Texas

2©© Corrpro. All Rights Reserved.Corrpro. All Rights Reserved.

For TodayFor TodayFactors that influence stray current corrosion generated from DC transit systemsThe consequences of transit stray currentControlling transit stray current at the sourceMonitoring for transit stray currentMitigating transit stray currentQ & A


Stray Current Corrosion – Electrically Continuous Pipe


Stray Current Corrosion – Electrically Discontinuous Pipe


Different Metals Corrode At Different Rates (Faraday’s Law)

Consumption RateMetal Pounds/Ampere-Year Steel 20 Lead 74

Copper 45 Zinc 23

Magnesium 8.8 Aluminum 6.4

Assumption: Constant, continuous electrolytic stray current discAssumption: Constant, continuous electrolytic stray current dischargeharge


Transit stray current varies over time, 24/7/365Transit stray current varies over time, 24/7/365

24 Hours

Track-to-Earth Potential (Volts)Rails discharging stray current ~100% of the time

TimeTime--Weighted AverageWeighted Average


Very Dynamic Track To Earth Potentials!Very Dynamic Track To Earth Potentials!

-120

-100

-80

-60

-40

-20

0

20

40

12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

TRACK TO EARTH

POTE

NTIAL (VOLTS)

-120

-100

-80

-60

-40

-20

0

20

4012:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

TRACK TO EARTH

POTE

NTIAL (VOLTS)

July 2007July 2007

May 2008May 2008


Yard/Shop Stray Current When Yard Is Connected To MainlineYard/Shop Stray Current When Yard Is Connected To Mainline

-600

-400

-200

0

200

400

600

10:00 AM 10:15 AM 10:30 AM 10:45 AM

AM

PER

ES

Stray current Stray current ““spikesspikes”” are not zero time durationare not zero time duration


Stray Current Corrosion EquivalenciesStray Current Corrosion Equivalencies

0

5

10

15

20

25

0 20 40 60 80 100 120 140 160 180

Time (seconds)

Voltage

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80 100 120 140 160 180

Time (seconds)

Volta

ge

Am

peresA

mperes

Corrosion = Current x TimeCorrosion = Current x Time


STEEL PIPE STEEL REINFORCING BAR

1 Square Inch Having 0.25-Inch Wall Thickness, Complete

Perforation

6-Inch Long Section of #4 Bar, 0.5-Inch Diameter, 50% Loss

1 Ampere 4.3 Days 10 Days

0.1 Ampere 43 Days 100 Days

0.01 Ampere 1.2 Years 2.8 Years

0.001 Ampere 12 Years 28 Years

0.0001 Ampere 120 Years 280 Years

CORROSION DETERIORATION

Time-Varying Stray Current Discharged From Structure To Earth, 30% Duty Cycle

How Much Corrosive Stray Current Is Too Much?How Much Corrosive Stray Current Is Too Much?


New Orleans New Orleans –– Saint Charles LineSaint Charles Line

0

100

200

300

400

500

600

700

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

AM

PER

ES

1985: 700 amps stray current = 47% of total propulsion current

2002: 500 amps stray current = 33% of total propulsion current

1985 – after ~9 years service

2002


PhiladelphiaPhiladelphia

STRAY CURRENT DRAINAGE CURRENT (AMPERES)

0

2000

4000

6000

6/ 18/ 01 12:00 AM 6/ 28/ 01 12:00 AM 7/ 8/ 01 12:00 AM 7/ 18/ 01 12:00 AM 7/ 28/ 01 12:00 AM 8/ 7/ 01 12:00 AM 8/ 17/ 01 12:00 AM 8/ 27/ 01 12:00 AM 9/ 6/ 01 12:00 AM

Weekdays Weekends


Valley Metro Valley Metro –– 20 Miles 20 Miles –– Opening December 2008Opening December 2008*** Designed for Less Than 1 Ampere Stray Current Per Mile ****** Designed for Less Than 1 Ampere Stray Current Per Mile ***


Other Consequences of DC Stray Current Other Consequences of DC Stray Current (Besides Corrosion of Rails, Pipelines & Other Structures)(Besides Corrosion of Rails, Pipelines & Other Structures)

“Free” cathodic protection (“consequence” or “benefit”?)Hydrogen embrittlement of pipelines & reinforced concrete structuresReduced cathodic protection system life and effectivenessNot in compliance with company SOPs and regulations, e.g. 49-CFR-192Spalling and softening of concrete (acid formation)Loss of electrical groundingElectrical shockFire, e.g. “slow-burn” 3rd rail electrical leakage (heavy-rail transit)Saturation of electric company transformer coresMalfunction of transit, freight & commuter rail signals & crossing gatesP-I-C (?)


D = distance between substation and loadRN = resistance thru negative conductors (rails)

RL = negative system to earth resistance at load endRS = negative system to earth resistance at substation end

IT = train operating currentIN = current returning thru negative conductorsIS = current returning thru earth

TPSSTPSSLoadLoad IITT IINN

Positive CircuitPositive Circuit

Negative CircuitNegative Circuit

RRLL IISS RRSS

DD

RRNNIISS

Simplified Transit Electrical ModelSimplified Transit Electrical Model


Transit System ModelingTransit System Modeling


Computer Simulations & Predictive ModelingComputer Simulations & Predictive Modeling

-125

-75

-25

25

75

125

9500 12000 14500 17000 19500 22000 24500 27000

Station Number

Str

ay C

urre

nt L

evel

s (m

A/1,

000

feet

)

-30

-20

-10

0

10

20

30

9500 12000 14500 17000 19500 22000 24500 27000

Station Number

Trac

k-to

-Ear

th P

oten

tial (

V)

Stray Current Levels - Multi-Loads

All Trackwork @ 250 Ohms-1,000 Feet

Track-to-Earth Potentials

Multi-Loads

Simulation: 6,610 ampere loads (trains) at 8 Stations


√ “Floating” negative return (ungrounded)

√ Traction substations close to passenger stations

√ Traction substations reasonably spaced

√ Continuously welded rail√ Track slab rebar electrically

continuous (“stray current collector”) and or epoxy coated

√ High resistivity concrete for track slab, e.g. silica fume additive

√ Yards electrically isolated from mainline

√ Relocated utilities designed with stray current control provisions

√ PRIMARY DEFENSE = High track to earth resistance - Valley Metro design/construction criteria = 250 ohms/1000 ft., minimum

√ O&M is essential

Controlling Transit Stray Current At The SourceControlling Transit Stray Current At The Source


Typical Insulated Track Designs

Boot Tie & Ballast

Direct Fixation


Stray Current On Pipelines


Transit Stray Current: What’s a Pipeline Corrosion Engineer To Do?

Include specific stray current control language and action levels in master utility relocation agreement with transit agencyDocument pipe potentials and currents before transit operations commenceRoutine (reasonable) surveillance once transit line is in service:

Thorough baseline survey shortly after transit operations beginInclude data collection during rain eventsBase testing locations on track-to-earth resistance data reported by transit agency; include crossovers and street crossingsEvaluate remote monitoring vs. manual data collectionParticipate in corrosion control coordinating committee

Easiest & Best Solution (my opinion) = Hire Corrpro!


Current/Potential DataloggersCurrent/Potential Dataloggers

2”

X/Y X/Y PlotterPlotter

22--Channel Channel Logger w/ X/Y Logger w/ X/Y

CapabilityCapability


Track-to-Earth Potential (Volts)Rails discharging stray current ~100% of the time

Pipe-to-Soil Potential (Volts) Pipe accumulating stray current ~100% of the time


Correlations Correlations –– ““Cause and EffectCause and Effect””

Vga Vgb VgcVgx Vgd+ +

+ ++Vga Vgb Vgc

Vgx Vgd+ +

+ ++

Ea Eb Ec+++ Ea Eb Ec+++

Vg1 = -0.0984EM – 0.4964

M 1 -++ -

Rails pickRails pick--up stray current, pipeline discharges stray currentup stray current, pipeline discharges stray current


Correlations Correlations –– ““Cause and EffectCause and Effect””

Vga Vgb VgcVgx Vgd+ +

+ ++Vga Vgb Vgc

Vgx Vgd+ +

+ ++

Ea Eb Ec+++ Ea Eb Ec+++

M+ - 5 -+

Vg5 = +0.0953EM – 0.4958

Rails and pipeline pickRails and pipeline pick--up stray currentup stray current


Stray Current Stray Current ““BetaBeta”” ((ββ) Profile) Profile


TimeTime--Weighted AveragingWeighted Averaging

-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

PIPE

TO

SO

IL P

OTE

NTI

AL

VAR

IATI

ON

(VO

LT)

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

Time Weighted Average Corrosive (+) Potential Variation +0.034 Volt

Time Weighted Average Protective (-) Potential Variation -0.042 Volt

Time-Weighted Average Change = 0.034 Volt, <20% of Maximum Variation


PipePipe--ToTo--Soil Potentials Soil Potentials –– Effective Monitoring/Detection Is EssentialEffective Monitoring/Detection Is Essential

-10

-8

-6

-4

-2

0

2

4

6

8

106:00 PM 7:00 PM 8:00 PM 9:00 PM 10:00 PM 11:00 PM 12:00 AM

PIPE

TO SOIL POTE

NTIAL (VOLT

S)

-10

-8

-6

-4

-2

0

2

4

6

8

10

6:00 PM 7:00 PM 8:00 PM 9:00 PM 10:00 PM 11:00 PM 12:00 AM

PIPE

TO SOIL POTE

NTIAL (VOLT

S)

March 2008March 2008

May 2008May 2008


““BiBi--Polar Stray CurrentsPolar Stray Currents”” 10+ Miles From Transit Line10+ Miles From Transit Line

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

012:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

PIPE

TO

SO

IL P

OTE

NTI

AL

(VO

LTS)


Probe & Coupon TechnologiesProbe & Coupon Technologies


Remote MonitoringRemote MonitoringProbe-Tag: 5500 K11A-1 Probe Type: PA-0.4-10-0.1-6 Probe serial No.: PA04270025Test initiated: 20-12-2005

0

100

200

300

400

500

600

700

800

900

1000

17/03/06 18/03/06 19/03/06 20/03/06 21/03/06 22/03/06 23/03/06 24/03/06 25/03/06

Date

AC c

urre

nt -

A/m

2C

orro

sion

rate

mic

ron/

y

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

JDC

A/m2

Uac (V)

Corrosion rate Uac Jdc


WhatWhat’’s a tolerable pipes a tolerable pipe--toto--soil potential shift?soil potential shift?

Typical corrosion engineer’s response:It all depends

Dale’s rules-of-thumb:< 0.05 volt – typically not a concern0.05 – 0.1 volt – could turn into a problem, increased monitoring required0.1 – 0.3 volt – further evaluation warranted to determine corrosion significance> 0.3 volt – likely a problem, mitigation appropriate


Water Pipe

Transformer - Rectifier

+ -

Anode Junction Box

Impressed Current Anodes

Stray Current Corrosion ControlStray Current Corrosion Control


V A+ -

RI

Stray Current Control using Galvanic AnodesStray Current Control using Galvanic Anodes

Install diode only when needed based on field testsInstall diode only when needed based on field tests


Stray Current Control using Potential Controlled RectifierStray Current Control using Potential Controlled Rectifier

-+

--+

1 -+


Transit System

Structure 1 Structure 2

Stray Current Stray Current Drainage Drainage

BondsBonds

Stray current drainage bonds can create an avalanching effect and

should typically only be used as a last resort


SummarySummaryLeft unchecked, transit generated stray currents can be horrendousStray current control at the source is the best long-term solution…proven technology existsStray current control maintenance and monitoring are essential by the transit agency and by neighboring facility operatorsThe level of monitoring by neighboring facilities (and related cost) is usually inversely proportional to the level of O&M by the transit agencyCorrosion control coordinating committees are a good forum for information exchange and resolution of problems (hopefully before they occur)

38©©Corrpro. All Rights Reserved.Corrpro. All Rights Reserved.

Thank YouQ & A

Dale [email protected]

(713)460-6040www.corrpro.com

mailto:[email protected]

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Stray Current Corrosion Control For DC Rail Transit Systems Stray Current Western... · Stray Current Corrosion Control ... Corrosion = Current x Time ... “Bi-Polar Stray Currents”