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Did you know?

Cathodic protection using impressed current systems was first implemented in 1928 after successful tests were carried out on gas pipelines in New Orleans.

Coating defect detection

With coating defect detection, a distinction must be made between coating holidays and contact with foreign objects. Basically, holidays are revealed by the results of potential and protective current measurements.

Proving the effectiveness of cathodic protection at every holiday requires these coating holidays to be located, and this is done by measuring potential gradients (potential distribution):

Protective current flows into the pipe at the location of the coating holiday and causes a voltage drop in the holiday's overall earth electrode resistance. In a spatial representation, this would be shaped like an funnel and can be detected using two probes set up on the ground in different places (ohmic coupling). The potential distribution pattern's maximum point is located at the point where the coating is damaged.

With the "IFO" coating defect detection procedure (special version of the CIPS method), the two reference electrodes are set up 10 meters apart across the pipe's axis, and the potential between the two electrodes is measured as the difference in the measured values between the ON and OFF phases. This measurement is then repeated in 5-meter intervals along the pipeline. When a coating holiday is encountered, the polarity of the potential being measured changes.

The location of foreign objects is established by determining the route that an AC or DC current applied to troubleshoot the pipe surface takes from its feed-in point to the coating holiday.