Integrity Management of Circumferential Cracking in Natural Gas Pipelines: Susceptibility Modeling and Inline Inspection

Abstract TC Energy’s first recorded circumferential cracking pipeline incident was a girth weld leak in 1961. Since that time, there has been a concerted effort to better understand the mechanism and manage the integrity threat of Circumferential Stress Corrosion Cracking (CSCC) and circumferential cracking in general. Hydrostatic testing has a limited ability to mitigate these features due to being parallel with hoop stresses and, if the loading is not reduced, circumferential features continue to grow, and will typically fail by leak. To date, CSCC has largely been managed through direct assessment programs or opportunistically combined with other integrity programs such as geohazard and stress management, direct examinations resulting from SCC and other threats, and failure investigations. When CSCC has been found and efforts have been made to analyse or mitigate the risk, operators have largely relied on susceptibility modeling, overlaying risk factors and selecting direct examination sites where the risk is estimated to be the highest. Key risk factors used in modeling and analysis are axial or bending stresses, especially in locations where they exceed hoop stress, pipeline movement, susceptible steel & coatings, and environmental factors that facilitate crack growth. TC Energy has undertaken several of these investigations in their natural gas pipeline network with limited success in finding circumferential cracking, and thus, continuous efforts are being made to improve the effectiveness of CSCC programs. While Ultrasonic Circumferential Crack Detection tools have been in commercial service for over a decade, their use in natural gas pipelines has been limited due to the requirement for a liquid medium, complicating an inline inspection (ILI) run’s execution, bringing a large operational risk to the pipeline system and gas delivery, and their subsequent cost. In 2022, TC Energy began testing the Micron ILI Technology® (Micron ILI) developed by Novitech Inc, (which does not require a liquid medium) and has seen success in detecting, identifying, and sizing circumferential cracking. This study will look at recent cases of verified CSCC found on the TC Energy natural gas pipelines with this novel ILI technology. The results will then be compared with previously used susceptibility modeling and any updated susceptibility information to establish any observed shortcomings within that method. A brief overview of the ILI tool technology, specifications, rigorous validation process at TC Energy, and observed limitations will be included for discussion. To date the total number of pipeline segments inspected with the MFL ILI for the assessment of circumferential cracking is still limited, therefore the available data set provides early indications of the findings. Additional runs and data will be used to evaluate the overall technology effectiveness and potentially to advance the currently available susceptibility model.