Constant Extension Rate Tensile (CERT) Tests of Creviced Alloy 600 Specimens in Aqueous Environments at 288 C

Constant extension rate tensile (CERT) tests on creviced tubular Alloy 600 specimens containing 0.1 M Na2SO4 demonstrated that overaging could restore resistance to intergranular stress corrosion cracking (IGSCC) in solution annealed material after furnace sensitization had dramatically increased this susceptibility. IGSCC occurred when chromium rich M23C6 carbides were present in the grain boundaries but absent from the grain interiors. Overaging coincided with combined intergranular and intragranular carbide precipitation. Tubing dimensions prevented a gage section reduction adequate for both acceptable mechanical performance and behavior representative of bulk material. However, the results presented here suggest that internally creviced specimens improve sensitivity for Alloy 600 in the CERT test. The internally creviced CERT test is especially convenient for studying the effect of contaminants on failure mode in a refreshed autoclave.