Evaluation of the API 579-1/ASME FFS-1 KCSCCL1 Global Bending Stress Intensity Factors

Abstract

Abstract The API 579-1/ASME FFS-1 2021 (API 579) Fitness-For-Service stress intensity factor solution for a cylinder with a long surface crack in the circumferential direction (i.e., 360 degrees), subjected to Pressure, a Net-Section Axial Force and Global Bending (KCSCCL1) was independently investigated in this work. Linear elastic finite element models of cracked cylinders subjected to various applied global bending stress fields were created and used to estimate stress intensity factors (K), from which were determined the respective influence coefficient values for global bending (G5). The comparison of the newly calculated values to the existing stress intensity factors shows reasonable agreement for larger internal radius to thickness ratios (Ri/t), but significant differences for low ratios representing thick wall cylinders. The new influence coefficients were also compared to values previously published in the literature for the parameter combinations that exactly overlap with API 579 for the Ri/t ≤ 10 parametric space. The new stress intensity factor equation and associated influence coefficient values presented in this work are recommended as an improvement for fitness for service assessments where Ri/t < 10. For thin wall cylinders, the existing API 579 approach for KCSCCL1 is acceptable.