Key Elements and Best Practice in the Management of Circumferential SCC

Abstract Circumferential SCC (C-SCC) is an emerging issue for the pipeline industry with no established management practice. Early experience indicated that C-SCC was strongly correlated to high axial/longitudinal stresses caused by geohazards. There is, however, growing evidence that the majority of C-SCC can be located in areas without identifiable geohazards. Effective management of this threat to the pipeline integrity needs a fresh approach. Most of the current industry practice and experience have been focused on axially-oriented SCC (A-SCC). C-SCC and A-SCC share certain commonalities, but there are several significant differences. For instance, the sources and magnitude of axial/longitudinal stresses that are a key factor for C-SCC management are different from those for hoop stresses. The availability and performance of ILI tools for C-SCC can also be different from those for A-SCC. This paper covers a few key elements in the management of C-SCC, including: • Susceptibility, • Growth rate, • Fitness-for-service (FFS) assessment, • Appropriate representation of safety margin in contrast to the concept of burst pressure (Pburst) or failure pressure ratio (FPR), and • Repair and mitigation options. Another key element, ILI technology for detecting and characterizing C-SCC, is also briefly discussed. The state of the art and gaps in technology and understanding in those key elements are noted. For instance, the conventional understanding of a safety margin for A-SCC in the form of FPR (FPR = Pburst / MAOP) is not valid for managing C-SCC. In contrast to the hoop stress, which is a primary driver for A-SCC, axial/longitudinal stresses in pipelines are not well understood. While axial/longitudinal stresses from geohazards are often cited as a key contributor to C-SCC, axial/longitudinal stresses from other sources can be more common. In some cases, the magnitudes of these stresses can be higher than those from geohazards. The characteristics of axial/longitudinal stresses can potentially affect the growth rates and dormancy of C-SCC, the choice of mitigation options, and safety measures in field work when mitigations are performed. This understanding of the axial/longitudinal stresses becomes a major part of C-SCC management, and thus is one of the focuses of this paper.