In strain-based design and assessment, accurate measurement of pipe longitudinal strain demand is a key element in performing proper strain assessments. Quick pipeline strain assessments are usually needed after widespread natural disasters such as earthquakes or heavy rainfalls that affect multiple lines at several sites. Finite Element Analyses (FEA) and In-line Inspection (ILI) tools are the most common methods to measure/estimate the longitudinal strain demand of in-service pipelines. However, because they are rather time-consuming methods, they cannot be relied on when quick fitness-for-service evaluations of pipelines is needed. ILI needs considerable amount of time for planning and preparation as well as post-run analyses, and FEA needs extensive efforts to gather input data which might not be readily available for each site.
Enbridge recently used a method of strain demand estimation during a rapid response process to several sites affected by lateral landslides after major weather events. The method involves gathering basic field measurements of pipe deformed shape and performing analytical strain calculation by using curve-fitted deformed shape functions.
This paper describes this method, its key elements, and the assumptions on which it is based. It also presents the evaluation of this method via FEA of several pipes, soil conditions, and landslides scenarios. And finally, it concludes the capability of this method for different cases of pipes and landslides.