Thermal Fatigue Testing and Analysis of a Thick Perforated Ring

Thermal fatigue cracking has been observed for thick perforated spacer rings used as part of a thermal fatigue test loop operating at Bechtel Bettis, Inc. The perforated rings are used for instrumentation access to the fluid flow at the test specimen inlet and outlet, and are subject to alternating hot and cold forced flow, low oxygenated water every three minutes so that rapid changes in water temperature impart a thermal shock event to the inner wall of the rings. Thermal and structural three dimensional elastic and elastic-plastic finite element analyses (FEA) were conducted for the ring and the results used to predict fatigue crack initiation using strain-based fatigue-life algorithms. Predicted cycles-to-crack initiation agreed well with the observed cracking when alternating shear strain intensity analogous to the Tresca stress was used. This analysis qualifies the use of FEA for thermal fatigue assessments of complicated three-dimensional components.