L51666 Surface Preparation and Coatings on the Susceptibility of Line Pipe to Stress-Corrosion Cracking

Abstract

Within the last decade, a number of gas pipeline companies throughout the world have identified the presence of Stress-Corrosion Cracking (SCC) on their pipelines. While the cause of the SCC resulted from a multitude of factors, there appeared to be a commonality relating to pipeline coatings. Although SCC has occurred under polyethylene/PVC tapes and enamel coatings, not a single incident has been recorded where SCC has occurred on a fusion-bonded-epoxy coated line. The three major factors that were thought to account for the difference in the SCC performance of the various coatings were; (1) resistance of a coating to disbonding, (2) the ability to pass current through the coating and thereby protect the disbonded regions and (3) the surface preparation of the line pipe prior to coating application. These factors were addressed in this three-year program for PRCI. This report examines the relationship between coatings and surface preparation and the likelihood of subsequent stress corrosion cracking. Standard Cathodic disbondment tests, measurements of potential gradients beneath disbonded coating, electrochemical measurements of current passages through coatings and actual SCC tests are described and results reported.