Transit stray current western region gas conference tempe 8.27.08

1
©©Corrpro. All Rights Reserved.Corrpro. All Rights Reserved.
Stray Current Corrosion ControlStray Current Corrosion Control
For 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 Today
Factors that influence stray current
corrosion generated from DC transit
systems
The consequences of transit stray current
Controlling transit stray current at the
source
Monitoring for transit stray current
Mitigating transit stray current
Q & A

Stray Current Corrosion – Electrically Continuous Pipe

Stray Current Corrosion – Electrically Discontinuous Pipe

Different Metals Corrode At Different Rates (Faraday’s Law)
Consumption Rate
Metal 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
TRACKTOEARTHPOTENTIAL(VOLTS)
-120
-100
-80
-60
-40
-20
0
20
40
12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM
TRACKTOEARTHPOTENTIAL(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
AMPERES
Stray currentStray 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)
Voltage
AmperesAmperes
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 OrleansNew 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
AMPERES
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 12:00AM 6/28/01 12:00AM 7/8/01 12:00AM 7/18/01 12:00AM 7/28/01 12:00AM 8/7/01 12:00AM 8/17/01 12:00AM 8/27/01 12:00AM 9/6/01 12:00AM
Weekdays Weekends

Valley MetroValley Metro –– 20 Miles20 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 CurrentOther 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
structures
Reduced cathodic protection system life and effectiveness
Not in compliance with company SOPs and regulations, e.g.
49-CFR-192
Spalling and softening of concrete (acid formation)
Loss of electrical grounding
Electrical shock
Fire, e.g. “slow-burn” 3rd rail electrical leakage (heavy-rail
transit)
Saturation of electric company transformer cores
Malfunction of transit, freight & commuter rail signals &
crossing gates
P-I-C (?)

D = distance between substation and load
RN = resistance thru negative conductors (rails)
RL = negative system to earth resistance at load end
RS = negative system to earth resistance at substation end
IT = train operating current
IN = current returning thru negative conductors
IS = current returning thru earth
TPSSTPSSLoadLoad IITT IINN
Positive CircuitPositive Circuit
Negative CircuitNegative Circuit
RRLL IISS RRSS
DD
RRNN
IISS
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
StrayCurrentLevels(mA/1,000feet)
-30
-20
-10
0
10
20
30
9500 12000 14500 17000 19500 22000 24500 27000
Station Number
Track-to-EarthPotential(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
agency
Document pipe potentials and currents before transit
operations commence
Routine (reasonable) surveillance once transit line is in
service:
Thorough baseline survey shortly after transit operations begin
Include data collection during rain events
Base testing locations on track-to-earth resistance data reported
by transit agency; include crossovers and street crossings
Evaluate remote monitoring vs. manual data collection
Participate in corrosion control coordinating committee
Easiest & Best Solution (my opinion) = Hire Corrpro!

Current/Potential DataloggersCurrent/Potential Dataloggers
2”
X/YX/Y
PlotterPlotter
22--ChannelChannel
Logger w/ X/YLogger 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

CorrelationsCorrelations –– ““Cause and EffectCause and Effect””
Vga Vgb Vgc
Vgx 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

CorrelationsCorrelations –– ““Cause and EffectCause and Effect””
Vga Vgb Vgc
Vgx 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 CurrentStray 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
PIPETOSOILPOTENTIALVARIATION(VOLT)
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 PotentialsSoil Potentials –– Effective Monitoring/Detection Is EssentialEffective Monitoring/Detection Is Essential
-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
PIPETOSOILPOTENTIAL(VOLTS)
-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
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
0
12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

Probe & Coupon TechnologiesProbe & Coupon Technologies

Remote MonitoringRemote Monitoring
Probe-Tag: 5500 K11A-1
Probe Type: PA-0.4-10-0.1-6
Probe serial No.: PA04270025
Test 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
ACcurrent-A/m2
Corrosionratemicron/y
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
JDCA/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 concern
0.05 – 0.1 volt – could turn into a problem,
increased monitoring required
0.1 – 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 CurrentStray Current
DrainageDrainage
BondsBonds
Stray current drainage bonds can
create an avalanching effect and
should typically only be used as a
last resort

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

Transit stray current western region gas conference tempe 8.27.08

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Transit stray current western region gas conference tempe 8.27.08

Similar to Transit stray current western region gas conference tempe 8.27.08 (20)

More from JORGE RODRIGUEZ Jrodriguezj2006

More from JORGE RODRIGUEZ Jrodriguezj2006 (20)

Recently uploaded

Recently uploaded (20)

Transit stray current western region gas conference tempe 8.27.08