Influence of Environment and Applied Stresses on the Susceptibility to Corrosion and Anodic Dissolution of α,β’-Brass in NaNO3 Solutions

α,β’-brasses, used for components in gas distribution network, are believed to be susceptible to simultaneous dissolution (Cu, Zn) and/or selective dissolution (dezincification) processes in corrosive environments. These phenomena are suspected to play a major role during the first stages (incubation and initiation) of SCC damage development observed on in service network components. In this framework, it is of interest to improve knowledge on kinetics and mechanisms of brass dissolution. The present study aimed at contributing to a better understanding of the dissolution processes of α,β’-brass, this topic being little studied to date.

The specimens, corresponding to α,β’-brass CuZn40Pb2 (CW617N), were machined from stamping rods used to manufacture gas transfer valves. The corrosion tests were performed in NaNO₃ solution selected with reference to research on α-brass (1). Two types of objectives were defined; the first corresponded to test the influence of environment (pH, nitrate ions concentration) and mechanical loading on the corrosion behaviour through electrochemical methods, and the second, to determine the dissolution and dezincification kinetics from immersion tests at constant potential, in selected environments and under specific loadings.

In order to reach the first objective, results obtained over a wide range of testing conditions (pH, nitrate ions concentration, loadings…) were analysed by comparing open circuit potential measurements, anodic polarisation curves, and surface characterizations (Optical Microscope, Scanning Electron Microscope and X-Ray photoelectron spectrometry). For the second objective, measurements of both the dissolution depths and the weight loss, chemical analyses of the corroded materials and the corrosion products (Inductively Coupled Plasma, Energy-dispersive X-ray spectroscopy) were used to quantify the dissolution kinetics. Finally, discussion focuses on understanding the dissolution mechanism, in comparison with α-brass dissolution process proposed in the literature (2). The influence of load on the basic mechanisms (opening of damages, stability of oxides layers....) will be discussed to better understand the SCC incubation and initiation stages.

1. S.A. Fernandez and M.G. Alvarez, Corros. Sci., 53, 82 (2011).

2. A.P. Pchelnikov, A.D. Sitnikov, I.K. Marshakov and V.V. Losev, Electrochim. Acta., 26, 591 (1981).

“This work was performed in the framework of a joint laboratory, called CETIMAT, where CIRIMAT and CETIM collaborate for some aspects of their research."