A Study on the Propagation of Chloride-Induced Stress Corrosion Cracking for Austenitic Stainless Steel at Corrosion Environment

Abstract

Austenitic stainless steels have been widely used in the petrochemical industry, nuclear power plants and the ship industry due to their high toughness and corrosion resistance. However, these materials are susceptible to environmentally-assisted degradation, such as chloride-induced stress corrosion cracking (CISCC). In this respect, this study investigated CISCC crack propagation rate for austenitic stainless steels, such as type 304L and type 316L, in the corrosion environment. Considering the environment of the spent nuclear fuel canister used in the dry storage system, the test chamber is always maintained at 3.5% NaCl and related humidity (RH) 95% at 60℃. For initiation of CISCC, a test procedure, which has nine pre-cracking procedures for a CT specimen, is suggested. In a test procedure, crack transitioning, which induces the environmental corrosion crack, is observed after mechanical precracking. To determine the CISCC crack length corresponding to each test step, the direct current potential drop (DCPD) method is measured in real-time. In addition, the CISCC crack observed after final fracture is measured using optical microscopy in order to improve the accuracy of the measured crack length. In the test results, CISCC crack resistance of type 316L is better than that of type 304L. Finally, the test results show that the CISCC crack propagation rate is 2.784E-11 m/s for type 304L and is 9.93E-11 m/s for type 316L.