Stress corrosion cracking of copper-nickel alloys in sulphide polluted natural seawater at moderate temperatures

Abstract

A stress corrosion study on copper-nickel alloys commonly used as condenser and heat exchanger materials in marine environments has been conducted in sulphide polluted seawater. The study aimed to determine the susceptibility of 90Cu10Ni and 70Cu30Ni alloys to stress corrosion cracking (SCC) in natural seawater with and without sulphide at moderate temperatures. The stress corrosion tests were carried out in a slow strain machine. The tests were performed over a range of temperature, 25–70°C, under a constant strain rate of 1.4×10 −6 S −1 in 200–3120 ppm S −2 in seawater solutions. The concentration range was chosen in a way to simulate the pollution impact of the oil spill and oil fires in the marine environment of Kuwait. The behavior of the alloys under various conditions has been evaluated by comparing the ratio of ultimate tensile stress, elongation, and time to failure of samples tested in solution to those tested in air. In addition, confirmation of SCC and the nature of the fracture mode has been achieved by applying metallographic techniques as well as by examination of the failed samples by a scanning electron microscope (SEM).