Wednesday, June 17, 2009

Anonymous has left a new comment on your post "Other comments on TM0497":

I have worked for a pipeline distribution company since 1988 in the corrosion department. We have both rectified and galvanic CP systems with various test point types. We were taught to keep the half cell as close to the pipe as possible while getting CP reads. Most of our test points were coated, steel risers so we would put the half cell next to the riser when getting reads. This minimizes IR drop, especially in the soil type we have which runs around the 3,000 ohm-cm range. We have always used the -850 mv criteria. While attending NACE courses, the instructors said that the more critical CP reading is around the -800 mv range but they somewhat account for the IR drop factor and used -850 mv. There are coated pipelines in our system that were installed in the early 1950's with CP on it from day one and I have only seen a few corrosion leaks which were due to interference situations. The key is to fix CP system shorts ASAP, have more test points than you think you need and get the readings as close to the structure in damp soil as possible.

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