Strain-based Design—Advances in Prediction Methods of Tensile Strain Capacity

In recent years, ExxonMobil has undertaken a comprehensive experimental and numerical program to characterize tensile strain capacity of welded pipelines under different operational, geometric and material property conditions. Key parameters affecting tensile strain capacity have been identified through sensitivity studies and used in a large-scale FEAbased parametric study to develop closed-form tensile strain capacity equations for different limit states. A key parameter affecting tensile strain capacity of welded pipelines is the tearing resistance (CTOD R-curve). Small-scale testing techniques have been developed to characterize the tearing resistance (R-curve) of full-scale pipelines using single edge notched tension (SENT) specimens. Experimental and numerical results have shown that the SENT R-curves closely match the full-scale test R-curves. The generalized tensile strain capacity equations have been validated against 20 full-scale tests for pipe grades X65 to X80 grades. The equations correctly predict the observed failure mode in the full-scale tests as well as the tensile strain capacity. Simplified, conservative tensile strain capacity equations with fewer parameters have been developed by making reasonable assumptions for several key parameters. The generalized and simplified tensile strain capacity equations can form the basis of a multi-tier engineering critical assessment (ECA) procedure for strain-based design of welded pipelines.