Evaluation of the API 579-1/ASME FFS-1 KSSCCL1 and KSSCCL2 Stress Intensity Factors

Abstract

Abstract The API 579-1/ASME FFS-1 2021 Fitness-For-Service stress intensity factor solution for a sphere with a surface crack, 360 Degrees, through-wall fourth order polynomial stress distribution (KSSCCL2) was independently investigated in this work. Axisymmetric, linear elastic finite element models of cracked spheres subjected to various applied stress fields were created and assessed. The objective was to estimate stress intensity factors (K) to evaluate crack-like flaws in spherical geometries using a parametric approach. The results were then used to calibrate the respective influence coefficient values (Gi). The sphere with a surface crack, 360 Degrees, internal pressure (KSSCCL1) uses the same table of influence coefficient values (Gi) and thus the new coefficients are also relevant to the KSSCCL1 scenario. A comparison of the newly calculated influence coefficient values to the existing values shows reasonable agreement for spheres with low ratios of internal radius to wall thickness (Ri/t). However, there is increasing discrepancy as the wall ratio increases, with the large differences predicted at Ri/t = 1000. The new influence coefficient values are recommended as an improvement for fitness for service assessments investigating 360-degree surface flaws in spherical geometries subject to fourth order polynomial through-wall stress fields (KSSCCL2) or internal pressure (KSSCCL1).