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Reliability Methods for Fracture Verification of Pipelines Subject to Lateral Buckling

Product Number: MPWT19-15030
Author: Abdul Rahman El-Chayeb, Faris Ragheb Kamal, Don Xiaodong Wang, Oussama Takieddine
Publication Date: 2019

Recent project experiences in the Arabian Gulf Region have shown that weld fracture is the governing limit state for subsea pipelines subject to lateral buckling loads. This is due to the small axial strain limits which can be allowed to minimize impact on weld repair rate for offshore pipeline installation. Considering the absence of reported weld fracture failures due to lateral buckling, it is possible that the safety margins used in fracture verification due to buckling can be further optimized. For instance, in a recent work scope to validate an existing pipeline for higher operating temperature it was found that the maximum allowable strain would be 0.252%. This was less than the 0.4% strain limit associated with radiographic NDT as considered at the design stage when the pipeline was installed in 2012. In other work scopes, the maximum allowable strain due to lateral buckling was 0.18% which is also significantly less than the historic 0.4% used in pipeline design codes and standards. The above supports the argument that although pipeline fracture analysis procedures are fully mature and well established, these procedures do not necessarily capture the complexities involved in dealing with pipelines susceptible to lateral buckling taking into account the statistical distributions of buckle location along the pipeline route, defect location, defect size, material strength, crack growth constants and a number of other parameters. This paper outlines a procedure for implementing fracture verification of pipelines susceptible to lateral buckling based on probabilistic approach. It is shown that this procedure can reduce the conservatism in the deterministic approach usually used and can help reduce unnecessary weld repairs during pipe-lay operations