This study employs three dimensional (3D) non-linear, finite element analysis (FEA) to supplement a critical flaw sizing assessment of an in-service reformer piping tee. The analysis is guided by the EDF (Électricité de France) Assessment Procedure R5 (formerly from British Energy Generation LTD. or BEGL) as well as Part 10 of API 579-1/ASME FFS-1. Specifically, Volume 4/5 of R5, which addresses crack growth, is used to determine the largest permissible flaw as a function of operational cycles and time at temperature. Required stresses are generated using FEA as well as the simplified reference stress techniques of R5 as appropriate. The analysis explicitly considers thermal transients, as well as cyclic plasticity. Furthermore, modeling of steady state operating conditions considers creep in the FEA material model. Additionally, creep-fatigue flaw growth is considered for a range of initial defect sizes. The targeted inelastic, non-linear FEA is leveraged to remove significant uncertainty and conservatism, and the simplified techniques of R5 are employed wherever reasonable to give the most efficient analysis possible. This investigation provides estimates of flaw propagation rates based on historical cyclic operation and permits determination of reasonable inspection intervals for the reformer tee in question.
Paper published with permission.