Effect of CO2 on Near-Neutral pH Stress Corrosion Cracking Initiation of Pipeline Steel

Near-neutral-pH SCC has been one of the major remaining concerns to pipeline safe operation. In order to improve our understanding of its initiation mechanism a comprehensive testing setup was used in this study. It was found that the initial near-neutral-pH environment under the disbonded coating of pipeline steel can vary significantly from near-neutral to high pH values. The pH value was strongly affected by CO₂ availability and the level of cathodic protection. When cyclic loading was applied in the stress corrosion cracking initiation tests, based on the local environment under the disbonded coating, different products from corrosion pits to surface micro-cracks were initiated on pipe surface up the gradient of cathodic protection.