Stress corrosion cracking in an Al-bronze chlorine gas regulating valve S.K. Das, B. Ravikumar, D.K. Bhattacharya, I. Chattoraj* National Metallurgical Laboratory, CRP Division, Jamshedpur 831007, India Received 28 June 1999; accepted 3 July 1999 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 identi®ed 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. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Stress corrosion cracking; Failure analysis; Aluminium bronze; Galvanic corrosion 1. Introduction One of the common and potent failure mechanisms of engineering components is stress corrosion cracking (SCC) which requires the simultaneous operation of corrosion and stresses. The two are synergistic, with stress causing crack opening and enhanced entry of the corrosive electrolytic media, so that even more corrosion occurs and the process becomes autocatalytic. Most metals and alloys show a speci®city of environment which causes SCC in them [1,2]. In dissimilar alloy or metal systems, especially when such alloys come into intimate contact electrically, a galvanic cell is set up with the less noble alloy corroding in preference to the more noble alloy. Such galvanic cells can activate stress corrosion cracking in appropriate systems where stresses are present. Aluminium bronzes have been used for dry chlorine services. The single phase (a) alloy, which has a Engineering Failure Analysis 7 (2000) 229±237 1350-6307/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S1350-6307(99)00027-8 www.elsevier.com/locate/engfailanal * Corresponding author. Tel.: +91-657-426091, fax: +91-657-426527. E-mail address: ichatt@csnml.ren.nic.in (I. Chattoraj).