Session: CS-03-02 Environmental Fatigue Issues (Joint M&F)

Paper Number: 65972

Start Time: Tuesday, July 13, 2021, 08:00 PM

65972 - A Fatigue Crack Growth Model for Type 304 Austenitic Stainless Steels in an Elevated Temperature Air Environment 

The ASME Boiler and Pressure Vessel Code, Section XI utilizes reference fatigue crack growth rate (FCGR) curves for flaw evaluations.  The current ASME reference curve for austenitic stainless steels in air environments is a Paris-Law relation with a single ΔK exponent that covers the entire ΔK range.  Since generation of the model that became the ASME reference curve, extensive additional FCGR testing of Type 304, Type 304L, and Type 304/304L dual-certified stainless steel and the corresponding weld metal has been performed in an elevated temperature air environment.  This testing revealed FCGR behaviors that were not adequately captured by the ASME reference curve.  In particular, the ASME reference curves failed to capture the flattening of the FCGR curve in the intermediate ΔK range before the FCGRs sharply drop off as the threshold behavior is approached.  Additionally, the FCGR data showed a slight frequency-dependence.  Based on this data, a new FCGR model was generated for Type 304 austenitic stainless steels in an air environment between 480°F and 640°F.  A tri-linear Paris-Law style correlation was chosen for the updated FCGR model to accommodate both the flattening of the FCGR curve at intermediate ΔK levels and the sharp downturn in the near-threshold ΔK regime.  Each of the three branches of the FCGR curve exhibits a different R-ratio dependence, with the near-threshold regime being most sensitive to changes in R-ratio.

Presenting Author: Kathleen Barron Naval Nuclear Lab

Authors:

Kathleen Barron Naval Nuclear Lab