ANALYSIS OF INFLUENCE OF HYDROGEN ON PITTING CORROSION AND STRESS-CORROSION OF AUSTENITIC STAINLESS-STEEL IN CHLORIDE ENVIRONMENT

A hydrogen development occurs inside the pit, even under anodic polarization conditions in a basic environment. The reason why the reaction H** plus plus e** minus yields H occurs can be explained by the fact that the electrochemical conditions (E, pH) inside the pit indicated on an E-pH diagram of iron are below the equilibrium line of H** plus /H. The hydrogen diffuses in the austenitic steel around the pit and causes: (1) an increased anodic reactivity, (2) transformations of the austenite into martensite and ferrite, (3) an embrittlement of the metal around the pit, and (4) a buildup of internal stresses in the metal.