AC Assessment, Corrosion Prediction, Safety and Mitigation Quick

AC Assessment, Corrosion Prediction, Safety and Mitigation Quick
AC Assessment, Corrosion Prediction, Safety and Mitigation
Quick Guide
By Joe Pikas
The NEW AC Mitigation PowerTool© now with unlimited pipeline and electric
transmission tower lines to truly understand, model and mitigate the underground
pipeline AC induced current integrity problem. The AC Mitigation PowerTool© has been
developed to assist the engineer or technician to model and mitigate or modify the
design of pipeline cathodic protection systems in order to reduce the AC current density
effects to meet the criteria specified either by a client or the National Association of
Corrosion Engineers (NACE) standard.
The Pipeline Research Council International (PRCI) AC Predictive & Mitigation software
developed by Electro Sciences, Inc. and Dr. John Dabkowski (PRCI Catalog #L51835)
has been the defacto industry safety & analysis standard since 1999. The PRCI AC
Predictive & Mitigation software was developed to handle multiple pipelines utilizing the
same right-of-way with overhead High Voltage (HV) Alternating Current (AC) power
lines. A NEW and enhanced version of the PRCI field proven and field tested
computational engine has been ported to work on current and future “cloud” and mobile
devices as well as the traditional desktop/laptop.
Now able to address Complex Corridors with Unlimited pipelines and high
voltage transmission lines can be assessed versus the limitation of the PRCI
Integrated Modeling can follow complex pipelines and tower lines that are
networked I.e. diverge or that intersect with each other.
Multiple scenarios can be run with Steady State, Faults or mitigation in minutes
o Multiple or Individual graphs
Ease of manual or Excel data input
o Can show data in total
Data can be visualized using graphs and Google Earth
Cloud or desktop version
Detailed reports show graphs with data
Ease of determining multiple mitigation cables and bonds
Integrate Google Earth with GIS capability for visualization of pipeline and tower
Faster computational modeling
o Steady State
o Faults with Arc Radius
o Mitigation
Input and Output to/from Excel and Google Earth
o Latitude/Longitude coordinates
Interim reports can be generated at any time in the process
Data validation and error checking
Change units of measurement at anytime
Operational defaults are built in for common tower settings
Mitigation design allows bonds and multiple mitigation cables
Electrical power lines carry an electrical current, where as a magnetic field is produced
around the wire which induces into the buried pipe. This linking causes an alternating
voltage and current to be induced onto a parallel collocated pipeline. When a pipeline is
located in the vicinity of a power line, it is subject to several electrical effects depending
upon the operational status of the line. In addition, lightning stroke or other cause, the
power line will experience a short circuit condition known as a fault. The focus of the
AC predictive guide is based on inductive coupling and fault conditions from co-located
power lines using Technical Toolboxes AC Mitigation PowerTool©.
1. AC Pipeline Prediction
a. Electrostatic Interference (Capacitive when pipe is above ground)
i. Function of voltage not current
ii. Transfer of small amounts of power to pipeline
iii. Can result in high voltages on short sections
iv. Considered nuisance voltages
b. Induced Voltages (Electromagnetic)
i. Function of tower current not voltage
ii. Power transfer is proportional
iii. Line current
iv. Length of parallelism
v. Inverse to separation distance
vi. Results in high voltages on long sections of pipeline
c. AC Faults
i. Rare in US
ii. Short duration
iii. Weather conditions
1. High winds
2. Lightning
iv. Structural failure
1. Poor maintenance
2. Accidental damage
3. Vandalism/Terrorism
2. AC Mitigation
a. AC Decoupling Devices, Polarization Cells and Surge Protection
i. Dairyland Devices (See Appendix B)
ii. Cu Cable for Parallel Grounding
iii. Distributed Ground Beds
iv. Discrete Ground Beds
b. Mitigation to NACE Standard <15VAC
i. Personnel Hazard
c. Gradient Control Mats at Pipeline
d. Appurtenances such as Test Stations & Valves
i. Grid with Zn, Cu
ii. Decoupler
Practical Approach to Mitigating Corrosion
1. AC potentials induced into a pipeline are a function of:
a. Inverse distance between these parallel structures
b. Pipe diameter
c. Coating conductance/resistance
d. AC tower loads
2. Induced AC into a pipeline or to earth is directly proportional to the strength of AC
tower current load.
a. Longitudinal electrical fields (LEF) are induced into the earth.
b. LEF can be field measured to estimate AC before a pipeline is constructed
3. Input Data
a. Tower Configurations
i. Single Circuit Horizontal
ii. Single Circuit Vertical
iii. Double Circuit Horizontal
iv. Double Circuit Vertical
b. Shield Wires
i. Cross sectional height and horizontal displacement of the shield
(sky) wires from the tower center line are evident inputs. Program
default accepts data for two wires with the assumption that the
wires are periodically grounded to the tower grounds.
c. Phase Wires
i. Physical placement of the wires, i.e., height and horizontal
displacement from the tower center line are obvious if and when
data are available. Default values for typical circuits as a function of
circuit voltage level are available from within the program data
d. Tower Data
i. Additional data required are the average tower ground resistance to
remote earth and the average separation between the faulted
transmission line towers (structures). Default values for these
parameters are shown below:
e. Pipeline Data
i. Diameter
ii. Sections as shown below
iii. Location
iv. Coating Quality
v. PRCI Guideline for Estimating Pipe Coating Resistance (Next
 (1-ohm m = 100-ohm cm)
 Coating resistance in Kohm -ft2
 Be careful of unit conversion
AC Corrosion
1. Current Density Criteria
a. Does not usually occur at AC current densities of less than 1.9 A/ft 2 (20
b. May occur at AC current densities of 1.9 – 9.3 A/ft2 (20 - 100 A/m2)
c. Can occur at AC current densities of greater than 9.3 A/ft2 (100 A/m2)
2. AC corrosion rates are:
a. Highest at holidays having a surface area of 0.155 – 0.465 in2 (1 - 3 cm2)
b. High CP
c. Chloride environments
1. Most common mitigation approach is the grounding of the pipeline by means of
buried horizontal wires, galvanic anodes, etc. See Screen Selection on next
a. Discrete (Ground Resistance and Node)
b. Distributed (Anode Resistance Times Spacing)
c. Parallel (Copper Cable(s) with De-Couplers)
d. Combinations of above
Note: Examples of Steady State and Fault Voltage and Current Drafts are shown
on the next two (2) pages.
Steady State Voltage and Current (Combined Graph)
Modified Calculation has been added to validate assessments to field measurements
and coating resistance estimations. Coating resistance is a primary factor in these
complex calculations.
Steady State with Mitigation with Distributed Ground Bed on Each End
(Individual Graph)
Fault Voltage and Current – Unmitigated (Individual Graphs)
Fault Voltage and Current with Mitigation (Individual Graphs)
AC Corrosion Calculations
1. High AC current density effects has resulted in AC corrosion.
2. AC modeling and mitigation is used to estimate AC voltage and AC current
3. AC current density can be calculated using a known area on a coupon.
4. Where
a. iAC = AC Current Density (A/m2)
b. VAC = pipe AC voltage to remote earth (volt)
c. ρ = soil resistivity (ohm-m)
d. d = diameter of a circular holiday
5. AC voltages as low as 1 VAC can produce high current densities at small
holidays in lower resistivity areas.
6. AC voltage required to for a current density of 100 A/m2 in 100 ohm-cm soil at a
1 sq cm holiday is: (See Chart below)
VAC = iAC x p x 3.1416 x 1sq cm /8
VAC = 0.393
AC Corrosion Chart: AC Voltage versus Holiday/Resistivity
The format developed for this AC Mitigation program makes many of the computational
functions and much of the data input very easy for the user, thus making these
calculations in an understandable way for unlimited pipelines and transmission towers.
This is a first in this area of complex mathematical modeling. For example, data input
for only one computer screen is required to exercise the program to assess the
following including reporting.
Steady state induction predictions
Fault induction predictions
Mitigation design
Export data through Excel
GPS mapping using Goggle Earth
Help Section
Reports – Most Completed with Additional in Future Release
Current Density Graphs - Future Release
Upload data through Excel – Future Release
This easy to use interface makes the use of this cloud based program viable for number
of potential users in your company than other available computer programs.
See Appendix A (Getting Started) for an example of an AC project.
Should there be any questions, training or consulting, please feel free to call:
VP P.L. Integrity
Joe Pikas
3801 Kirby Dr. Suite 520, Houston, TX 77098
C 832 758-0009 Preferred
O 713 630-0505 X-216
Appendix A
Getting Started with skyBox Tools
Logging in:
Select Steady State: (No Data)
Load Case: Example 1 P & 2 T and Press Go
Example of 1 Pipeline and 2 Power Transmission Lines:
160 KV
Power Line
345 KV Power Line
6” Dia. Pipeline
Menu Bar Selections:
Transmission Lines
o Add
o Edit
o Delete
Example of Pipelines:
Menu Bar Selections:
Transmission Lines
o Add
o Edit
o Delete
o Show Full Section (See Below)
Show Full Section:
Calculate Steady State Graph and Download Report:
Modified Calculation has been added to validate assessments to field measurements
and coating resistance estimations. Coating resistance is a primary factor in these
complex calculations.
Fault Current – Load Fault Case:
Calculate Fault Current, Arc Distance and Download Report:
Modified Calculation has been added to validate assessments to field measurements
and coating resistance estimations. Coating resistance is a primary factor in these
complex calculations.
Mitigation – Sample Using Distributed Anode Ground Beds:
Load Saved Mitigation and Determine Best Strategy Using Cloud Base Interface:
Use a computational iterative process
Review principles and grounding techniques for mitigation
o Sunde Equations
o Dwight’s Curves
Use Technical Toolboxes Training and Consulting for complex circuits and
Use modified calculation to validate field measurements
Fault Current Mitigation Using Distributed Anodes:
Steady State Mitigation Using Distributed Anodes:
Reports – Steady State Voltage and Current with Mitigation
Reports – Fault Voltage and Current with Mitigation
Mitigation Considerations:
Types of grounding are reviewed:
(1) Discrete grounds such as deep wells can be used to mitigate widely
spaced voltage peaks or nodes.
(2) Distributed vertical or horizontal anode strings are used at nodes or
isolated voltage peaks. Distributed grounding such as a parallel horizontal
buried copper wire bonded to the pipeline can be used (See paragraph 3
below for additional details on de-couplers). This approach is used more
often used when multiple closely spaced voltage peaks exist on the
pipeline and to isolate grounding from the CP system. Both of these
approaches are accommodated by Cloud Based computer program. This
program requires an iterative procedure to determine an effective final
design and requires successively reruns with new mitigation resistance
values until a satisfactory reduction in the induced voltage levels is
(3) Wire or long line copper cable(s) using a bonded horizontal cable i.e. 1/0
or greater as the grounding element. This grounding system provides a
grounding impedance to achieve the best or lowest bound to achieve
satisfactory steady state voltage levels. Dairyland De-couplers and
related devices are used to isolate the grounding copper cable, anodes,
ground mats, etc.
(a) Copper grounding cables with and without backfill connected to
Dairyland de-couplers have a history of good performance record with
trouble free operations.
(b) Zinc ribbon grounding has been used in the past; however, limitations
due to being part of the CP system have resulted in performance
(4) Combinations of grounding can be used that are based on geometry of
pipes and transmission lines and soil resistivity constraints.
Note: For additional AC Mitigation training and consulting, call Technical
Toolboxes or visit our website
1) PR-200-9414 AC Predictive and Mitigation Techniques – Final Report
Appendix B
AC Mitigation System Checklist
Inductive voltage mitigation equipment:
 Decoupler
 Grounding material (bare copper, zinc, etc.)
 Isolated conductors connecting Decoupler and grounding material
 Conductor attachment method: thermite welding, pin brazing, plus
coating/sealing system
 Enclosure or pedestal for Decoupler
 Disconnection means for Decoupler testing or close interval surveys (Isolation
switch). Select switch with AC steady-state and AC fault ratings equal to the
Decoupler ratings.
Measurement equipment:
 Test station
 Coupon for AC current density measurement (or multiple function coupon)
Step and touch voltage protection near above-grade structures and connections:
 Gradient control mat
 Thermite welding molds/charges
 Anode for mat protection
 Decoupler for zinc grounding mat isolation from pipeline
 Isolated conductor
Isolating joint protection – subject to AC induction:
 Decoupler
 Decoupler mounting brackets appropriate for insolated joint type
Note: Dairyland Solid-State Decoupler (SSD) and Polarization Cell Replacement
(PCR) data and information are on the next page for mitigation selection.
Dairyland Solid-State Decoupler (SSD)
AC RMS 60Hz Fault Current Ratings
1 cycle
3 cycles
10 cycles
30 cycles
Conductor Size
All SSD Models:
AC- RMS, 60Hz steady-state current rating: 45A
Environmental Rating: IP68
Hazardous Location Rating: Division 2 and Zone 2
Dairyland Polarization Cell Replacement (PCR)
AC-RMS 60Hz Fault Current Ratings
1 cycle
3 cycles
10 cycles
30 cycles
Conductor Size
All PCR Models:
AC- RMS, 60Hz steady-state current rating: 45A (Optional 80A)
Environmental Rating: NEMA 4X (Optional NEMA 6P)
Hazardous Location Rating: Division 2 and Zone 2
Application notes for AC mitigation:
Select AC fault current rating that exceeds modeled or calculated values
expected on pipeline.
Select standard AC steady-state current rating unless modeled or measured
conditions require the higher 80A PCR rating.
Most AC mitigation sites are classified as Div. 2/Zone 2 or are "ordinary"
locations. A Div. 2/Zone 2 product will cover either. If Div. 1/Zone 1 ratings are
needed, use model PCRH.
Apply product environmental ratings suitable for the site location. Most are
typically above grade and not subject to flooding. If below grade, select IP68 or
Select conductor size to match or exceed Decoupler AC fault current rating.
Note: For more information contact
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