Further Investigation of the API 579-1/ASME FFS-1 KPECL Stress Intensity Factors Available to Purchase

The API 579-1/ASME FFS-1 2021 Fitness-For-Service (API 579) stress intensity factor solution for a plate with an embedded crack, infinite length, through-wall fourth order polynomial stress distribution (KPECL) was further investigated. The new findings presented in this paper are built upon the findings and proposed API 579 updates presented in 2022. Current API 579 guidance is that the KPECL solution can be used as an acceptable approximation for a cylinder with an embedded crack, circumferential direction, 360 Degree, through-wall fourth order polynomial stress distribution (KCECCL) when the ratio of the internal radius (R_i) to wall thickness (t) is greater than or equal to five, R_i/t ≥ 5. API 579 also makes the same recommendation for the corresponding case of a cracked sphere geometry (KSECCL). As part of the investigation, KCECCL influence coefficient values and KSECCL influence coefficient values were calculated for R_i/t = 5 and are presented in this paper. A comparison of the new results to the previously reported KPECL influence coefficients are presented. For both curved geometries, it was determined that the KPECL influence coefficients proposed in 2022 are reasonable approximations for R_i/t ≥ 5, however a few scenarios were identified where this practice may under-predict the stress intensity factor by a few percent. The new influence coefficient values are recommended as options for fitness for service assessments that involve either the KCECCL scenario or the KSECCL scenario with R_i/t ≥ 5.