Product Ideas and Enhancements

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Toughest CP challenge

In a remote north eastern area, we have a steel gas main with multiple abnormally low CP reads. Installed in 1983, the 8’’ pipe is protected with a sacrificial cp system and is coated with a two layer polyethylene coating using shrink sleeves at the girth welds. Functioning insulating joints are located at the city gate station exit and at all entrances of the gate stations

A close interval survey with a 10ft spacing was performed on the cp main with cp reads ranging from -1.05 to -1.15Vcse. However, multiple locations (roughly 100ft in length) were noted ranging from -0.5 to -0.6 Vcse. Similar reads were taken using a different test station and on a different day.

One local business had underground conduits protected with a rectifier. This rectifier was interrupted and a survey was done over on the pipeline. The foreign rectifier had negligible influence on the pipe. We then passed a pipe locator using a 120 hz filter to find any rectified voltage on the pipe. None were found.

A DCVG and ACVG survey were conducted over the line to find any coating holidays. Negligible signals were found indicating any major coating holiday. The soil resistivity using a 4 pin Wenner method was around 3500 Ω●cm at pipe depth (both parallel and perpendicular to the pipe).

Direct assessment digs were then done on three locations. The pipe coating was in a near perfect state. We then proceeded to install two 32lbs high potential magnesium anodes and a new test station at each site. The excavation was backfilled with new material.

The following month, the pipe potential stayed roughly the same and the anodes were reading around -0.8 Vcse and around 3 mA DC of current flowing towards the pipe.

We are looking at installing CP coupons and doing a soil analysis even though the backfill was new material only.

What do you believe could be the problem with this pipeline?

  • Guest
  • Jul 16 2019
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  • Admin
    Christopher Shawhan commented
    30 Aug, 2019 06:54pm

    Thank you for posting a tough CP challenge! We will be reaching out for some additional information if needed. We also look forward to providing your answer at the User Group event in October. See you there!

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