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

An analysis of the failure of a dry chlorine gas regulating valve made of A 1-bronze is presented. The valve had a stainless steel spindle within its c hamber. Cracks had initiated in the inner chamber walls and proceeded outwa rds resulting in leakage. The corrosion products on the crack surface were found to be a chloride-hydroxide complex of copper. This suggested the ingr ess of moisture along with the gas. The corrosion mechanism was identified as complex galvanic coupling between the dissimilar alloys which also resul ted in depassivation of the spindle surface. The stresses for crack propaga tion had come from the contact stresses as well as gas pressure on engageme nt of the spindle with the valve body. (C) 2000 Elsevier Science Ltd. All r ights reserved.