A Comparison of U-bend and Slow Strain Rate Procedures for Assessing the SCC Resistance of Type 304 Stainless Steel in High-Temperature Water

The effects of temperature, chloride content, and dissolved oxygen content on the susceptibility to stress corrosion cracking (SCC) of type 304 stainless steel in high-temperature water have been investigated. Both U-bend and slow strain rate stress corrosion tests were performed, complemented by electrochemical polarization curve measurements and extensive oxide film analyses by Auger electron spectroscopy (AES). The U-bend data showed decreasing susceptibility to cracking with increasing temperature, which correlated with thicker oxide films and greater enrichment of chromium in the films. In contrast, the slow strain rate tests (SSRTs) indicated maximum susceptibility to cracking at 250°C in the temperature range 200 to 300°C and the susceptibility to cracking increased with increasing oxide thickness. The extent of chromium and nickel enhancement in the oxide layers were different for the two specimen types tested in equivalent environments. Greater enhancement of nickel occurred in films formed on SSRT specimens than on U-bend specimens. It is concluded that the choice of test procedure for acquiring accelerated test data may be influenced by whether the components to which the data will be applied are likely to experience plastic strain during use.