Crack Initiation, Propagation, and Arrest in 316L Model Pipe Components under Thermal Fatigue

Abstract

Abstract There is a continuing need for reliable thermal fatigue analysis tools to ensure that high safety levels are maintained in the main coolant lines of light water reactors. As a contribution to this effort, a combined experimental and numerical investigation has been conducted on cylindrical components of 316L stainless steel subjected to cyclic thermal shocks of varying intensity. It exploits a dedicated rig in which the tubular test pieces are subjected to induction heating and water quenching. Under the applied loading, a network of cracks initiates at the inner surface; some of these propagate further through the wall thickness. The number of cycles to crack initiation is estimated from surface replicas taken during intermittent stops, whereas the crack depth of fatigue cracks is measured using an ultrasound time of flight diffraction technique (TOFD). The analysis is done by a sequentially coupled thermal-stress finite element analysis using a cyclic plasticity model. Predictions of the crack initiation life (based on crack initiation curves as well as crack propagation models for microstructurally short cracks) are in good agreement with the test results. Crack propagation for small fatigue cracks was estimated by plastic strain amplitude based propagation formulas, whereas long crack propagation is analyzed by Paris law type criteria using ΔK as well as ΔCTOD.