Effect of Pigging Damage on Sulfide Stress Corrosion Cracking of Corrosion Resistant Alloys

Hard wire brush pigging of oil and gas pipelines is often used to remove deposits and maintain flow efficiency but there is uncertainty as to whether the resulting mechanical damage could introduce a risk of localized corrosion or stress corrosion cracking. In this study, three different corrosion resistant alloys (CRAs) commonly used in oil and gas pipelines were subjected to surface abrasion at different levels of severity to simulate the damage experienced during pigging. Resistance to sulfide stress corrosion cracking under representative sour oilfield conditions was then evaluated using the four-point bend test method. No increase in susceptibility to stress corrosion cracking as a result of the simulated pigging process was observed under a range of conditions close to the pass/fail boundary for each material. Furthermore, under more severe conditions, surface abrasion inhibited local initiation and propagation of cracks on 25Cr superduplex stainless steel, with a ground surface finish, as a result of the compressive residual stresses created during the scratching process. The absence of pitting associated with pigging scratches was supported by electrochemical scratch repassivation measurements that demonstrated rapid repassivation of the 22Cr duplex stainless steel surface following the simulated pigging process. These results imply that the risk of stress corrosion cracking as a result of hard wire brush pigging of CRA pipelines is low.