Proposed New Fatigue Design Curves for Austenitic Stainless Steels, Alloy 600 and Alloy 800

Abstract

The current fatigue design curve for austenitic stainless steels in the ASME Boiler and Pressure Vessel Code is known to be unconservative in certain fatigue regimes. This design curve was based on data which included cold worked material, and it allows cyclic stresses which are too high to satisfy code safety margins for annealed materials in these regimes. New fatigue design curves are proposed for air environments based on the existing worldwide database for annealed materials. Because of the differing properties of the range of materials covered by the current fatigue design curves, separate fatigue design curves are also proposed herein for Nickel Based Alloys (Alloy 600 and Alloy 800) in air. In addition, high temperature (> 360°F, 182°C) water has been found to accelerate fatigue crack propagation rates and to have a very deleterious effect on fatigue longevity in the low and intermediate cycle regimes. New fatigue design curves which include high temperature water environmental effects are proposed based on the extensive data developed by investigators worldwide.