ASME PVP conference papers from 2007 and 2008 (References [1] and [2]) discuss fatigue analyses related to 304 stainless steel instrumentation spacer rings (rings) that had cracked while installed in a thermal fatigue test loop. The rings contain circular radial penetrations extending through the ring that allow access for instrumentation probes to monitor the fluid temperature and pressure. Routine inspection of the test loop revealed actively growing cracks in each port that appeared to start near the inner diameter (ID) of the ring. In this work, three-dimensional finite element analysis (FEA) thermal and fully-elastic structural Abaqus models were made from the available test measurements. The commercial crack modeling software, Franc3D, was used to complete an M-integral based fatigue crack growth (FCG) analysis. An assumed initial crack was inserted in a single port of interest near the ID of the FEA model. The crack was explicitly grown in an automated fashion over iterative growth steps. The explicit FCG analysis was able to match the directional path and final flaw size seen in the destructive evaluation metallographic images of the rings with the assumed input parameters exceptionally well, including shifting directions and splitting the crack without need of user input. The results of this work indicate that an explicit FCG analysis is feasible for a non-trivial thermal-structural problem.

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