Pitting resistance of candidate materials for nuclear-desalination plants

Pitting behaviours of four candidate materials for heat exchangers in nucleardesalination plants, such as titanium, super-austenitic stainless steels, duplex stainless steel, and Cu/Ni (70/30wt%) alloy were investigated. To evaluate and compare the pitting resistance of the materials, potentiodynamic polarization tests were performed in 3.5% NaCl solution. First, using the pitting potentials of the materials determined from the tests and surface observations, the pitting resistance of the materials was qualitatively compared. The analysis of the polarization curves showed that, among the electrochemical parameters of materials, the electric charge over the potential range until the pitting potential could be a constant at a combination of given material and environment, which implies that it would be one of the pitting parameters of materials. In this study through the analysis of the potentiodynamic polarization behaviours of an alloy, a new parameter, relative time for stable pitting (tsp), was established. And this parameter is suggested as a parameter by which materials pitting resistance can be compared in a quantitative manner in terms of the design life of structures made of the materials.