Evaluation of the API 579-1/ASME FFS-1 KPECL and KCECLL Stress Intensity Factors

The API 579-1/ASME FFS-1 2016 Fitness-For-Service stress intensity factor solution for a plate with an embedded crack, infinite length, through-wall fourth order polynomial stress distribution (KPECL) was independently investigated in this work. Finite element models of cracked plates subjected to various applied stress fields were created and used to estimate stress intensity factors (K), which were then used to calibrate the respective influence coefficient values (Gi). The comparison of the newly calculated values to the existing values shows reasonable agreement for some values and a substantial difference for others. The new influence coefficients were also compared to values published by Le Delliou and Barthelet (2007) for the parameter combinations that exactly overlap with API 579-1/ASME FFS-1 2016. Excellent agreement was found with the new values presented herein. API 579-1/ASME FFS-1 2016 also recommends that the KPECL solution can be used for a cylinder with an embedded crack, longitudinal direction, infinite length, through-wall fourth order polynomial stress distribution (KCECLL) when the ratio of the internal radius (Ri) to wall thickness (t) is greater than or equal to five. As part of this work, influence coefficient values were also calculated for Ri/t = 5 and are included in this paper. A comparison of each KPECL value to its respective KCECLL value indicates that the recommendation is a reasonable approximation. The new influence coefficient values are recommended for fitness for service assessments that involve either the KPECL scenario or the KCECLL scenario where Ri/t ≥ 5.