Methodologies for Establishing the Probability of Pipeline Failure at Slope Crossings

Pipelines in transmission pipeline networks often traverse land slopes along the right-of-way; especially near water crossings. While the vast majority of these slopes are stable, some might have a potential for instability related movements. Accordingly, pipelines subjected to these movements are susceptible to strain overload which may cause loss of containment in terms of buckling and/or tensile elongation failure modes. In order to analyze the risk of failure of pipelines due to slope movement it is beneficial to establish probabilistic approaches that can predict the likelihood of failure at each site given both aleatory and epistemic uncertainties. Estimation of such likelihood would support prioritization of integrity mitigation actions and confirm pipelines’ safety. There is a gap in pipeline literature in terms of available probabilistic approaches to analyze, assess, and manage such an integrity threat. Two probabilistic approaches are presented herein; a qualitative ranking analysis of slope hazards (QuRASH) and a semi-quantitative analysis of slope hazards (SQuASH). QuRASH is a qualitative approach that adopts site scores based on available slope characteristics, historical movements, expert opinion, and mitigation strategies. SQuASH is a reliability-based explicit limit state approach. Both approaches were applied to a large simulated sample of slope crossings that exhibit characteristics representative of North America transmission pipeline slope crossings. The resulting probabilities of failures were directly compared to those predicted based on expert judgement. The high ranked sites compared favorably with those evaluated by experts to exhibit elevated threats. This successful comparison provides a certain level of confidence in the proposed approaches.