Notch Fatigue Crack Initiation in High Temperature Water Environments: Experiments and Life Prediction

Abstract

Test results, experimental techniques and analytical interpretations are reported from notched compact type (CT) tests of SA 333 Gr. 6 carbon steel to determine quantitatively fatigue initiation lives in high temperature oxygenated water. Parameters explored include environments of air, 0.2 ppm O2 and 8 ppm O2-water at 10.3 MPa (1500 psi), temperatures of 149, 232 and 288° C, frequencies of 0.00021, 0.0021 and 0.021 Hz, notch radii of 0.051 and 0.51 mm and R-values of 0.2, 0.5 and 0.8. Pseudostress amplitudes were calculated elastically and by Neuber notch analysis procedures using a worst case notch concept. Results were compared to ASME Section III fatigue data curves. Test results showed that the fatigue initiation life of carbon steel is substantially lowered as oxygen level is raised, as frequency is lowered or as temperature is raised. No frequency or temperature effect occurred in air. To a lesser extent, a decreasing notch radius or an increased R-value degrade the initiation life. Results compare favorably with interpretations based on environmental fatigue crack growth of this material.