Premature Failures of Copper Alloy Valves and Fittings in the New York City Water Supply System

摘要

Copper alloys are used in various water main components in The New York City Water Supply System. Three copper alloys have been found to fail prematurely. Two manganese bronzes, Copper Development Association (CDA) alloys C86500 and C86300, have previously been found to fail in valves and shaft caps as well as nut fasteners in transgranular and intergranular stress corrosion cracking (SCC) modes, respectively. A valve stem, made of alloy C86500, has just recently been found to fail what appears to be from SCC, but in a combination of transgranular and intergranular modes. Tapping goose necks, and a pressure regular stem made of CDA alloy C83600, have been found to fail prematurely. Failure analyses of the goose necks and the pressure valve stem have been performed; they appear to have failed from SCC with the lead reacting with water. The lead may create an environmental health problem by being absorbed by the potable water and supplied to the buildings they are serving. To corroborate the aforementioned failure analyses, specimens made of alloy C86500 and C83600 were machined from a valve stem and a goose neck respectively and tested in a laboratory with simulated environments. This paper presents the case histories of the two SCC type failures and what action is being taken to remedy these problems.