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Impressed Current Interference

Impressed Current Interference. Western Regional Gas Conference 2008 Tempe, Arizona By Paul Sedlet, Accurate Corrosion Control, Inc. Summary of Presentation. Definition of impressed current interference Identification of stray current influence Testing and documenting interference

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Impressed Current Interference

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  1. Impressed Current Interference Western Regional Gas Conference 2008Tempe, ArizonaBy Paul Sedlet, Accurate Corrosion Control, Inc.

  2. Summary of Presentation • Definition of impressed current interference • Identification of stray current influence • Testing and documenting interference • Consideration during new pipeline design • Coatings • Shielding • Test/Bond facilities • Solutions for interference • Bonding (Two Examples) • Magnesium Anodes (One Example) • Texas method

  3. Definition of Impressed Current Interference • From 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.

  4. Identification of Interference • Note 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.

  5. Example- Coating or Suppression from a Foreign Operator?

  6. CIS Crew at Test Station

  7. Design to Reduce Interference • Location • Proximity to existing foreign groundbeds • Consideration of others when locating new groundbeds • Coatings • Coating potential current pickup areas • Shielding or Non-Conductive Barriers • Physical barriers between pipelines at crossings • Test and Bond Facilities • Wires and soil tubes installed during construction

  8. Solutions to Interference-Bonding Solutions

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

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

  11. Investigation of above location Using Waveforms (Influence Study)

  12. Same Location After Bonding

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

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

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

  16. IR Span Waveform at Leak Site

  17. Using Waveforms to Indentify Suppression from Various Operators at Leak Site

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

  19. CI Waveforms Used to Indentify Specific Suppression from Foreign Operators

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

  21. Magnesium Anode Solutions

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

  23. N Gas Line 84” PCCP Pipeline Example- Magnesium Anode Installation at Crossing Anodes Terminated to Water Company to provide low resistant electrolytic path of Gas Co. current back to Gas Co. Pipeline • Legend • Gas Line Soil Tube • Water Line Soil Tube • Test Station/Anode Termination • #32 Magnesium Anode

  24. Inside PCCP- Electromagnetic Inspection

  25. Installing the Magnesium Anodes and Wires

  26. Magnesium Anode Interference Solution Configuration Gas Co. CP Current

  27. Watering the Soil Tube

  28. Test Station with Shunt

  29. 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.

  30. Texas Solution-Fight Fire with Fire

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