Stress corrosion cracking in an Al-bronze chlorine gas regulating valve

Abstract

An analysis of the failure of a dry chlorine gas regulating valve made of Al-bronze is presented. The valve had a stainless steel spindle within its chamber. Cracks had initiated in the inner chamber walls and proceeded outwards resulting in leakage. The corrosion products on the crack surface were found to be a chloride–hydroxide complex of copper. This suggested the ingress of moisture along with the gas. The corrosion mechanism was identified as complex galvanic coupling between the dissimilar alloys which also resulted in depassivation of the spindle surface. The stresses for crack propagation had come from the contact stresses as well as gas pressure on engagement of the spindle with the valve body.