Avoiding catastrophic corrosion failure of stainless steels (CORINOX)

The focus of the project was the development of a comprehensive way of assessing the risk for localised corrosion of stainless steels. Pitting, crevice corrosion, stress corrosion cracking and crevice-crack interactions were evaluated in terms of the effects of temperature, chloride concentration, potential, pH and cold work. The main emphasis was on the testing of the austenitic 1.4404 and the superduplex 1.4410 in solutions of NaCl and MgCl2. An intercomparison of the electrochemical test methodologies between laboratories was carried out and refined until consistent results were obtained. Pre-exisiting data for the two grades of interest were compiled and the environmental conditions prevailing in different applications were characterised. Measurement of pitting potentials and critical pitting temperatures gave reasonable agreement, while spring-disc crevice formers yielded lower critical temperatures for crevice corrosion than use of a modified flushed-port cell. The presence of crevices was found to have only a marginal influence on the development of stress corrosion cracking, and results from U-bend and slow strain rate testing were largely compatible. Results from field testing gave generally good agreement with laboratory data, but could in cases result in higher limiting conditions for localised corrosion. The results have been compiled into design diagrams defining the regimes in which there is a danger for different types of localised corrosion as a function of the main variables, chloride concentration and temperature. This provides indicative information for materials selection and a framework into which future data from both laboratory testing and field testing can be included.