Influence of pH on the crevice corrosion and stress corrosion cracking behavior of 304 stainless steel

Abstract

Crevice corrosion, weight loss, and stress corrosion tests were performed on 304 stainless steel. Crevices of various aperture sizes exposed to 45% magnesium chloride demonstrated the development of acidic conditions. As the aperture size was decreased, the pH of the solutions inside the crevices decreased. Weight loss tests showed that dissolution occurred in samples exposed to boiling 25% magnesium chloride acidified to various levels. As the pH of the 25% magnesium chloride was decreased, more dissolution occurred. No measureable weight loss occurred in samples exposed to unacidified magnesium chloride. Anodic dissolution was concluded to be the cause of the acidification observed in the crevicesStress corrosion tests performed on wedge-loaded compact tension specimens exposed to acidified (ph = 1.00) and unacidified (pH = 5.75) hot 45% magnesium chloride solutions showed similar crack initiation and propagation characteristics. These results suggest that acidic conditions developed at the initiation sites of the samples exposed to the unacidified solutions and were responsible for the observed dissolution sites. Both intergranular and transgranular fracture patterns were observed and were similar to those observed in the presence of hydrogen-assisted crack growth. Such observations suggest that hydrogen plays a role in the stress corrosion behavior of stainless steel exposed to magnesium chloride solutions.