Western Regional Gas Conference 2008Tempe, Arizona

By Paul Sedlet, Accurate Corrosion Control, Inc.

Summary of PresentationDefinition of impressed current interferenceIdentification of stray current influenceTesting and documenting interferenceConsideration during new pipeline design

CoatingsShieldingTest/Bond facilities

Solutions for interferenceBonding (Two Examples)Magnesium Anodes (One Example)Texas method

Definition of Impressed Current InterferenceFrom NACE SP 0169 definitions

Interference: Any electrical disturbance on a metallic structure as a result of stray current.

Impressed Current: An electric current supplied by a device employing a power source that is external to the electrode system. (An example is direct current for cathodic protection.)

Stray Current: Current through paths other than the intended circuit.

Identification of InterferenceNote areas of unexpectedly low potentials during

monitoring.Identify potential sources of stray impressed

current (could be same Company if the systems are isolated).

While monitoring the low potential, measure the change in potential when the suspected source is interrupted; measure foreign current on your pipeline; measure potential gradients.

Look at big picture to identify and test for pick-up and discharge areas.

Example- Coating or Suppression from a Foreign Operator?

CIS Crew at Test Station

Design to Reduce InterferenceLocation

Proximity to existing foreign groundbedsConsideration of others when locating new

groundbedsCoatings

Coating potential current pickup areasShielding or Non-Conductive Barriers

Physical barriers between pipelines at crossingsTest and Bond Facilities

Wires and soil tubes installed during construction

Solutions to Interference-Bonding Solutions

Example 1- Using CIS to Identify Possible Suppression, Waveform Testing to Identify Suppressing Operators and Bonding as a Solution

Example CIS- Possible Suppression Identified at MP 18 plus 147-feet

Investigation of above location Using Waveforms (Influence Study)

Same Location After Bonding

Example 2- Using Waveforms to Investigate Low Potentials at a Leak Site with Bonding Solution

P/S Waveform at Leak Site with Resist Bond Only to Foreign Operator

P/S Waveform at Leak Site with Full Bond to Foreign Operator

IR Span Waveform at Leak Site

Using Waveforms to Indentify Suppression from Various Operators at Leak Site

Close Interval Waveforms (50ft) to Identify Scope of Suppressed Area

CI Waveforms Used to Indentify Specific Suppression from Foreign Operators

“As Found” and “After Bonding”- Potential Profiles

Magnesium Anode Solutions

Example- Gas and Water Line Crossing with Magnesium Anode Interference Solution

Example- Magnesium Anode Installation at Crossing

Gas Line

84” PCCP Pipeline

N

Legend

Gas Line Soil TubeWater Line Soil TubeTest Station/Anode Termination

#32 Magnesium Anode

Anodes Terminated to Water Company to provide low resistant electrolytic path of Gas Co. current back to Gas Co. Pipeline

Inside PCCP- Electromagnetic Inspection

Installing the Magnesium Anodes and Wires

Magnesium Anode Interference Solution Configuration

Gas Co. CP Current

Watering the Soil Tube

Test Station with Shunt

Example- Magnesium Anodes at Crossing

DATA Pipe-to-soil potentials at crossing using new soil tubes 3-23-07 3-23-07 5-10-07

Wire Code As-Found (volts) As-Left (volts) Follow Up (volts)Water Co. White Tape -0.076 -0.661 -.850 I/O -.570

Gas Co. Yellow Tape -0.800 -1.143 -1.480

Mag. Anodes Red #14 -1.642 600mA 675mA

Note: Cycling Rectifier (3-23-07)-

Gas Co. Rectifier ON- Magnesium anodes output 590mA

Gas Co. Rectifier OFF- Magnesium anodes output 238mA

The data indicates approximately 352mA of Gas Co. current returning through the magnesium anodes back to the Gas Co.

Texas Solution-Fight Fire with Fire