Download AC Interference on Pipeline from Power Line Fault

AC Interference Mitigation
and Monitoring
Dale Lindemuth, P.E.
Director of Engineering
Houston, Texas
FOR TODAY
AC interference causes and concerns
Mitigation techniques
Mitigation project example
AC corrosion / PRCI research
Monitoring
Q&A
Utilidors Come In All Shapes and Sizes – 69kV to 1,000kV
(69kV and lower typically not a major concern, but can be)
2
Steady-State AC Interference on Pipeline
from Changing Electromagnetic Field:
SAFETY & CORROSION CONCERNS
Time-Varying
Electromagnetic
Field Produced By
AC Current In
Overhead Lines
(300-5,000
Amperes, 24/7)
Soil
Pipeline
AC corrosion rates
as high as 400 mpy
(10 mm/yr)
!
Ingredients for AC corrosion:
• AC power lines (or other AC)
• High quality coating
• Low soil resistivity
• Excessive CP/DC on pipe
AC Interference on Pipeline from Power Line Fault:
MAINLY SAFETY CONCERNS, ALSO COATING & EVEN PIPE
DAMAGE (Limited Reported Cases)
Fault Current – 10,00040,000 Amperes total
not uncommon, <0.1
second duration
Pipeline
Shield
(“Sky”) Wire
To Adjacent
Towers
Counterpoise
Cable To
Adjacent
Towers
AC Interference on Pipeline from Power Line Fault
Underground High-Voltage AC Transmission Systems
Copper Ground
Cable (Typ.)
A
C
B
B
C
A
Steady
-State
Pipeline
Pipeline
A
C
B
B
C
A
Power
Line to
Ground
Fault
Utilidors – Joint Pipeline / Power Line Corridors
1. Rights-of-way are increasingly difficult to obtain for new pipeline projects and
for new power line projects
2. An attractive option is shared rights-of-way, i.e. “utilidors”:
• New and upgraded power lines in existing pipeline corridors
• New pipelines in existing power line corridors
3. Future projections are for more and more utilidors
4. Advances in pipeline corrosion protection coatings reduce the grounding
(“earthing”) often associated with older generation coatings:
•
•
•
•
Reduced cathodic protection current demand (a good thing)
Unsafe AC voltages (a bad thing)
Increased propensity for AC influenced corrosion (a really bad thing)
Increased need for AC mitigation ($$$$)
5. Good neighbors, “do no harm”:
• Who is “responsible” for controlling AC interference?
• Who pays initially?
• Who pays long-term?
8
Measured Pipe Potentials Under
Power Line Steady State Operations
AC Volts
60
40
20
0
9
AC PIPE-TO-SOIL POTENTIAL (Volts)
Datalogging reveals conditions overlooked by
instantaneous (“spot”) measurements
30
25
20
15
10
5
0
12:00 PM
6:00 PM
Midnight
12:00 AM
6:00 AM
Noon
12:00 PM
6:00 PM
Midnight
12:00 AM
Knowing and tracking power line operations is essential
11
AC Mitigation & Control - North American
Standards/Codes and Regulations
•
•
•
•
•
•
•
NACE International – Corrosion Engineering Professional Society
IEEE – Institute of Electrical Electronic Engineers
CSA – Canadian Standards Association
US Federal Regulations CFR 192 & 195
US DOT Operator Qualifications (OQ)
Operator In-House Requirements
Typical Corrpro Project Requirements:
• 15 VAC Above and Below Grade (Steady-State)
• 3,000 – 5000 VAC during Fault for FBE
• AC Current Density < 30 amps / sq.meter (SP0169)
• New NACE Standard under development (TG430) to address AC corrosion
based on probe AC/DC current density and corrosion rate
(Corrpro/MetriCorr/Elsyca research for PRCI)
How far is far enough?
• 1 meter per kilovolt rule-of-thumb:
• 138kV = 450 feet
• 230kV = 750 feet
• 500kV = 1640 feet
• European standards:
• Overhead rural – 3000 feet
• Overhead urban – 1000 feet
• Underground, rural & urban – 150 feet
• Typical consultant’s answer: it all depends, pay us to study it
October-2015 INGAA Report (66 pages)
14
October-2015 INGAA Report – lots of look-up graphs
15
Many Complex Factors Contribute to AC
Interference & Determining Effective Mitigation
Pipeline:
• Pipeline vs Transmission Line Geometry and Proximity
• Length of Parallelism and Crossings
• Coating Quality (better quality coating causes increased AC interference,
but is also easier to mitigate when there is a problem)
• Cathodic Protection (excessive CP can increase corrosion rates in
presence of high AC levels)
• Magnitude and Variation in Soil Resistivities
• Electrical Breaks in Pipeline, e.g. Isolation Flanges
• Influence of Existing Nearby Pipelines
Power Line:
• Transmission Line Conductor Configuration
• Transmission Line Phase Transpositions
• Tower grounding and Shield/Sky Wires Connecting Towers
Parallel Mitigation, e.g. Zinc ribbon or copper cable, is often the
primary mitigation measure for new pipelines (Best Value)
17
Grounding with Galvanic Anodes
Overhead AC Transmission Line
Underground Pipeline
Sacrificial Anodes
Induced Voltage
Without Anodes
With Anodes
Distance
Deep Anode Grounds – Typically 50-300 Feet Depending on Design
1)
2)
3)
4)
Zinc ribbon
Magnesium ribbon
Copper cable
High-silicon cast iron
anodes in coke
breeze
5) Galvanized steel
water pipe with
threaded joints (???)
19
So what does AC mitigation cost?
New construction – parallel mitigation - $7-$9/Ft.
Existing pipelines – parallel mitigation - $18 - $30/Ft.
“Point mitigation” - $10K - $25K per location
depending on design needs
20
PROJECT EXAMPLE: Proposed 42” Pipe,
170 Miles, 7 Power Line Circuits to 500kV
21
Computer Simulations – Without Mitigation
RIGHT OF WAY SCHEMATIC
5
AC Circuit 3 - 115KV
AC Circuit 7 - 500KV
AC Circuit 2 - 230KV
AC Circuit 6 - 500KV
AC Circuit 1 - 500KV
AC Circuit 5 - 115KV
Cypress Pipeline
AC Circuit 4 - 230KV
4.5
Crossings not shown for clarity
4
3.5
3
2.5
2
1.5
1
0.5
0
0
20
40
60
80
100
120
140
160
140
160
STEADY STATE PIPE TO EARTH VOLTAGE - NO MITIGATION
120
VOLTS
90
60
30
15-Volt Maximum
0
0
40
60
80
100
120
MAXIMUM PIPE TO EARTH VOLTAGE UNDER FAULT CONDITIONS - NO MITIGATION
12,000
VOLTS
20
8,000
4000-Volt Maximum
4,000
0
0
20
40
60
80
100
22
CONSTRUCTION MILEPOST
120
140
160
Computer Simulations – With Mitigation
RIGHT OF WAY SCHEMATIC
5
4.5
Crossings not shown for clarity
4
3.5
3
AC Circuit 3 - 115KV
AC Circuit 7 - 500KV
AC Circuit 2 - 230KV
AC Circuit 6 - 500KV
AC Circuit 1 - 500KV
AC Circuit 5 - 115KV
Cypress Pipeline
AC Circuit 4 - 230KV
2.5
2
1.5
1
0.5
0
0
20
40
60
80
100
120
140
160
STEADY STATE PIPE TO EARTH VOLTAGE - WITH MITIGATION
VOLTS
30
Single Ribbon Mitigation
Double Ribbon Mitigation
15-Volt Maximum
20
15-Volt Maximum
10
0
0
20
40
60
80
100
120
140
160
MAXIMUM PIPE TO EARTH VOLTAGE UNDER FAULT CONDITIONS - WITH MITIGATION
Single Ribbon Mitigation
Double Ribbon Mitigation
4000-Volt Maximum
VOLTS
4,000
4000-Volt Maximum
2,000
0
0
20
40
60
80
100
23
CONSTRUCTION MILEPOST
120
140
160
Is the AC mitigation working?
STEADY STATE AC PIPE TO SOIL POTENTIAL WITH MITIGATION
20
Design, Computer Simulation at Peak Power Demand
Installed, Actual
VOLTS
15
10
5
0
0
20
40
60
80
24
100
120
CONSTRUCTION MILEPOST
140
160
Corrpro In Action: Multi-Channel AC/DC Close Interval Potential Survey
(data every 2.5 feet)
Corrpro-Unique Multi-Channel AC/DC
Close Interval Potential Survey (data every 2.5 ft.)
26
Common AC Corrosion Thresholds
AC Current Density
AC Corrosion Significance
Less than 2-3 A/Ft.2 (20-30A/Sq.M)
No or Low Likelihood
3 – 10 A/Ft.2 (30-10A/Sq.M)
Medium Likelihood
Greater than
10 A/Ft.2 (100A/Sq.M)
Very High Likelihood
Even in the Presence of Apparently
Effective CP
Qualitative only! Nothing about rate of
corrosion, which is what really counts! Right?
Coupon Potential & Current Measurements
(-)
mAac/dc
(+)
(+)
Vac/dc
on / instant-off
PIPE
COUPON REF.
(-)
AC Current
Density
(A/sq.m or
A/sq.ft) =
Measured
Current /
Coupon
Surface Area
Refined Criteria from PRCI Research
Average AC Current Density (A/Sq.M)
iAC vs. iDC, and or ER probe corrosion rate
Average DC Current Density (A/Sq.M)
Corrosion rate
Measuring is knowledge
DC ‘On’ potential
MetriCorr Logger
with Remote
Monitoring Option
DC IR compensated Potential
DC current density
AC potential
AC current density
Spread Resistance
Ref.
Electrode
Pipeline
MetriCorr Probe
Flush type
Rod type
Time-stamped, simultaneous data collection, as frequent as 1 set of
readings (7 channels of data) every minute
Examples from the field:
Modest level of CP does protect, even under high AC
Examples from the field:
With high AC, too much CP increases corrosion
Examples from the field
Impact of temporarily disconnecting AC mitigation for CP surveys
** Don’t do it! **
~470 mils/year!!!
Corrosion
Rate
DC Pipe-to-Soil
Potential
DC Current Density
AC Pipe-to-Soil
Potential
AC Current Density
CONCLUSIONS
1.
2.
3.
4.
AC interference can be accurately predicted.
AC interference can be safely and economically mitigated.
• With good engineering, there is no technical basis to seek alternate
pipe or power line routes because of AC interference.
AC mitigation systems can be reliably monitored and maintenance
friendly.
• Practical mitigation designs with pipeline operator input is essential.
In the presence of AC, excessive CP or cathodic DC interference can
increase corrosion rates dramatically.
• AC corrosion can be controlled in part by optimizing CP levels – not
too little, not too much, just enough.
Thank you…Q&A
Dale Lindemuth, P.E
(832)474-5361
[email protected]
Effective AC Monitoring Technique?
VICIOUS CIRCLE OF AC CORROSION
Induced AC
Small defect
Too much CP
Pre-requisites
Depolarization
Increased
AC current
Ohm’s law
Increased CP
SELFFEEDING
AUTOCATALYTIC
CORROSION
Reduced Spread resistance
Alkalinity
What’s it called?
Corrpro: ACIM = AC Interference Mitigation
Power industry: EMI = Electromagnetic interference
Dale: AC interference
What’s going here?
If you focus on corrosion
rate, the rest is secondary
VDC-ON (Volt)
VDC-Instant Off (Volt)
iDC DC Current Density (A/Sq.M)
VAC (Volt)
iAC AC Current Density (A/Sq.M)
Rs Spread Resistance (Ohm-Sq.M)
Personnel Safety: Equipotential Gradient Control Mats at Corrosion Control
Test Stations, Valves & Other Aboveground Fixtures
Test Station
Parallel Ribbon
& Mat
connected to
pipe through
DC-decoupler,
a.k.a “PCR” or
“SSD”
7’x7’ Zinc Ribbon Mat
“Spiral” – 8 inches below
grade under well-drained
gravel pad
Pipeline
Parallel Zinc Ribbon
Main Line Valve, Pig Launcher/Receiver, Fence Grounding
41
Characterizing Soil Resistivity
Low resistivity = High AC corrosion; High resistivity = More mitigation needed
RIGHT OF WAY SCHEMATIC
AC Circuit 3 - 115KV
AC Circuit 7 - 500KV
AC Circuit 2 - 230KV
AC Circuit 6 - 500KV
AC Circuit 1 - 500KV
AC Circuit 5 - 115KV
Cypress Pipeline
AC Circuit 4 - 230KV
5
4.5
4
Crossings not shown for clarity
3.5
3
2.5
2
1.5
1
0.5
0
0
20
40
60
80
OHM-CENTIMETER
OHM-CENTIMETER
APPARENT RESISTIVITY
10000000
1000000
100
120
140
160
Average 1-1.5-2.5 Feet
Average 4-5-6.5 Feet
Average 10-15 Feet
Average 25-40-50 Feet
Average 65-75-100 Feet
Average - All
100000
10000
1000
0
20
40
60
80
100
120
140
160
CDEGS EQUIVALENT RESISTIVITY
100000
10000
1000
0
20
40
60
80
100
CONSTRUCTION
MILEPOST
42
120
140
160
CEN-EN 15280 AC Corrosion Criteria
1 A/m2 (DC) – cathodic current
J AC
3
J DC
30 A/m2 (AC)
Since AC-influenced corrosion is related to AC & DC, criteria for pipes with CP
will be related to a combination of AC and DC current density using
coupons…or a tolerable corrosion rate determined using suitable ER probes
PRCI RESEARCH: CEN-EN 15280 AC Corrosion
Criteria Vs. Precision ER Probe Corrosion Rate
• ER data set from 31 pipelines, 218 points
• From US, South America, Europe & Asia
• 20% of ER data doesn’t conform with AC/DC current density criteria
• Analysis is input to PRCI AC corrosion guidance
How Best to Detect/Monitor AC
and DC Interference?
OR
Simple
Coupon
OR
Simple Electrical
Resistance (ER)
Corrosion Rate
Probe
Complete Monitoring
System – Sophisticated
Technology but
Straightforward to Use
Established Electrical Resistance (ER)
Corrosion Rate Technology
R (Ω)
w
d
L
R  ρm (T) 
L
W d
ρm (T)  ρm (T0 )  (1  α)T T0
As “d” (element thickness) is reduced because of corrosion, resistance is
increased. Resistance increase over time can be related to corrosion rate
(assuming constant temperature).
Tools in the ACIM Tool Box
Corrpro’s engineering strength is knowing which tool to use when and why
• Safe Engineering Services ACIM ($60K):
• Right-of-Way (soil resistivity profile)
• Hi-Freq (single soil resistivity)
• PRCI ACIM ($6K)
• Elsyca ($60K):
• IRIS (AC interference & mitigation)
• ACCorSolver (AC corrosion)
• CatPro (CP and DC interference)
• Spreadsheets
• Field evaluations and simulations
• Good ole engineering experience
• Existing AC interference issues vs. proposed
pipelines/powerlines
Existing 180-Mile Pipeline
26 Power Line Circuits to 230kV