Corrosion Fatigue Testing of Low Alloy Steel in Water Environment with Low Levels of Oxygen and Varied Load Dwell Times

Abstract

Corrosion fatigue testing of a low alloy steel was undertaken to determine the effect of cycling parameters and low oxygen levels on the crack growth rate at various stress intensity factor ranges. Notched, pre-cracked compact tension specimens were prepared from A516-90 plate material with a sulfur content of 0.020 wt%. These specimens were tested in a water environment with a pH of ~9.0 and a temperature of 177 °C. At each stress intensity factor range, the crack growth rate was compared at three different frequencies with oxygen levels <10 to 150 ppb. At higher stress intensity factor ranges, no effect on crack growth rate from oxygen, rise time, or dwell time was observed. For the lower stress intensity factor ranges, the crack growth rate decreased with oxygen addition and additional dwell times at maximum load. The decrease in crack growth rate at lower stress intensity factors is attributed to crack tip blunting and/or crack closure effects from oxide build-up. At the higher stress intensity factors, the mechanical crack driving force was sufficient to break the oxide and continue growing the crack.