Key Elements to Consider When Managing Circumferential SCC In Pipelines

Abstract In recent years, stress corrosion cracking (SCC) has become a more prevalent threat to pipeline integrity worldwide; SCC only occurs in a specific combination of a susceptible material, environment, and tensile stress at a particular location. In pipeline systems, the main SCC driving stress — from internal pressure — favors axial rather than circumferential SCC (CSCC). However, under certain conditions, such as excessive soil loads, high residual axial stresses from construction, etc., axial loading can reach the threshold for CSCC to initiate and propagate. Although in a smaller proportion when compared to axial SCC, CSCC incidence has also increased in the pipeline industry. Similar to any other integrity threat, a holistic approach is required to manage it; once a pipeline has been identified to be susceptible to CSCC, the next stage is to assess its extent in the system, understand the pipeline locations with active CSCC, and implement adequate repair and mitigation actions. Using only crack ILI to assess the extent of CSCC in a pipeline can be challenging due to limitations in currently available ILI technologies, especially for gas pipelines. Thus, direct assessment becomes a key supporting task at this initial stage of the management process; combining relevant data sets will help to define areas more susceptible to CSCC. Combining this information with ILI outcomes, when available, will help to develop and implement a more effective management plan. Although SCC direct assessment industry guidance is available, a CSCC-focused susceptibility model should be developed for each pipeline. This paper describes a proposed approach to managing CSCC in pipelines, which combines applicable data based on CSCC specific drivers, such as geohazards and construction features along the pipeline, pipe material data and cathodic protection (CP) performance. Hence, different layers of information are considered, including the pipeline data book and available ILI datasets (e.g., MFL, geometric inspection, historic CP surveys, visual inspections, and field verification data). In fact, this document includes a review of the main factors affecting CSCC in a gas pipeline with the aim of identifying those that should be considered in the susceptibility model; it also includes an example of elements considered for a specific pipeline whit CSCC present. Furthermore, it reviews the relevance of ILI when dealing with this threat, available ILI technologies and their possible limitations, and uncertainties and how to manage them. Finally, relevant mitigation and other actions aimed to manage this threat are also discussed.