Abstract
A new set of reference stress solutions for cracks in thick-wall cylinders were computed for addition in the next edition of the API 579-1/ASME FFS-1 standard, and are described in this paper. The geometry cases used ratios for the cylinder radius, wall thickness, crack depth, and crack length. The crack locations included axial, circumferential, internal, and external cracks. 3-D crack meshes were generated for each case to compute J-integral versus pressure result trends, which were used to determine the reference stress.
The Failure Assessment Diagram (FAD) method uses reference stress solutions to compute the Lr ratio on the FAD x–axis to evaluate cracks for plastic collapse; the FAD y-axis Kr ratio evaluates fracture failure. The elastic-plastic J-integral reference stress method will be briefly reviewed using results from this project.
A stress-strain curve was selected to represent typical material used for high-pressure components. The computed reference stress was shown to depend on the yield strength to tensile strength ratio, and a ratio of 90% was selected for use in this project.
Some shallow internal cracks in the thicker cylinder cases showed unexpected behavior in the J-integral versus pressure results, which prevented the reference stress from being computed. An alternative method was developed to use the maximum converged pressure as the nominal load to obtain reference stress solutions for those cases.
