Technical Note: Effect of Specimen Thickness on Cracking Susceptibility of Alloy 600 in High-Temperature Water

The effect of specimen thickness on the environmental crack growth rate (CGR) of alloy 600 (UNS N06600) in high-temperature water was studied. Results showed the environmentally induced CGR in high-temperature water did not change when the alloy 600 specimen thickness changed from 1 mm to 6 mm. Loading that enhanced plane stress conditions promoted transgranular (TG) cracking, and loading that reduced plane stress conditions promoted intergranular (IG) cracking. Results suggested that the criteria for fracture mechanics plane strain testing are too restrictive (conservative) for environmental testing purposes.