Development and Application of a Semi-quantitative Risk Assessment Approach for External SCC Integrity Assessment in Oil and Gas Pipelines

Abstract Since 1960s, numerous high and near neutral pH external Stress Corrosion Cracking (SCC) failures occurred in pipelines within Oil and Gas and other industries. To avoid such failures, multiple external SCC susceptibility criteria has evolved and been used including soil content, pH, coating type, Maximum Allowable Operating Pressure (MAOP), operating temperature and proximity to compression stations. While such criteria are present with successful empirical and field results, there has been limited methodology to readily and repetitively assess and risk rank pipelines susceptible to external SCC. To address this challenge, a semi-quantitative risk assessment methodology was devised covering more than ten probability of failure factors and four consequence factors. The methodology was applied to thirty pipelines transporting crude oil and natural gas liquid. A total of eight pipelines were ranked to a high-risk, whereas nineteen and three pipelines were at medium and low risk levels, respectively. An integrity assessment using UT Crack Detection (UTCD) and Electromagnetic Acoustic Transducer (EMAT) Inline Inspection (ILI) was applied to evaluate the risk assessment methodology results. The integrity assessment detected external SCC at 62% of high-risk pipelines, 42% at medium risk pipelines whereas no SCC was detected at pipelines at low risk level.