Performance evaluation of above ground surveys for locating external corrosion in pipelines

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Performance evaluation of above ground surveys for locating external corrosion in pipelines

Ward, C.R. / McCallum, M. / Masters, G.L. / Francis, A.

Integrity management regulations require operators of high-pressure gas pipelines to consider various threats to pipeline integrity including time-dependent degradation due to corrosion. Depending on factors including age and operating pressure, a pipeline will require periodic integrity assessment. Methods available for assessing external corrosion are in-line inspection, pressure testing, or Direct Assessment, which is the subject of this paper. An analysis was conducted on data from a large diameter gas transmission pipeline built in the 1960's. A 30 Km section was investigated, using data spanning an 18-year period. The records analyzed included above ground surveys, high-resolution in-line inspection surveys, and site investigations. Assuming the in-line inspection represents true condition, it was found that the above ground surveys produced indications at between 80% and 90% of the in-line inspection features. Approximately 35% of the survey indications did not correspond to in-line inspection features. This information should benefit those wishing to implement Direct Assessment programs using Structural Reliability Analysis techniques.