Continued Advancements Regarding Capacity Prediction of Strain-Based Pipelines

In areas of large ground movements, pipelines may be subjected to large longitudinal strains. It is imperative that strain-based design methods are developed for such pipelines. As reported previously, a comprehensive experimental and numerical program to characterize the tensile strain capacity of welded pipelines was undertaken. Models were developed that are capable of predicting strain capacity based on input parameters such as pipe geometry and properties, internal pressure, weld flaw geometry, weld properties, and high-low misalignment. These models (equations) have been validated against a data base of about 50 full-scale pipe strain tests that included a broad range of geometries and pipe grades (8–42″, 13–25mm, X60–X80). In the current paper, further developments are described. A pressure factor has been incorporated into the models. Whereas the previous models assumed that the circumferential stress from internal pressure was 80% of the specified minimum yield strength (SMYS) of the pipe, the pressure factor allows the calculation of strain capacity as a function of pressure that results in hoop stresses from zero to 80% of SMYS. Additionally, ranges for pipe yield-to-tensile ratio and weld tearing resistance curves (R-curves) have been expanded. New equations and associated flaw assessment diagrams for example cases are provided.