Mitigation of stress corrosion cracking of AISI 304 stainless steel in oxygenated water at 289(deg)C by organic species at low concentration.

摘要

In constant-extension-rate tests on sensitized AISI 304 stainless steel (SS) at 289(degree)C, some organic substances (oxygen scavengers) in feedwater containing (approximately)0.2 ppm dissolved oxygen decrease effluent oxygen concentration, electrochemical potential (ECP) of the steel, and stress corrosion cracking (SCC) susceptibility to very low levels. Other organic substances neither decrease oxygen concentration nor ECP of the steel significantly, but also mitigate SCC susceptibility relative to that in high-purity oxygenated water. The latter species apparently block active sites where cathodic reduction of oxygen occurs and thereby limit anodic dissolution of metal at the crack tip in a slip-dissolution mechanism of crack advance. In SCC tests on fracture-mechanics-type specimens under high-load-ratio, low-frequency cyclic loading conditions at 289(degree)C, the organic inhibitors at a concentration of (approximately)1.0 ppm stop crack growth in the sensitized steel, but are not effective in oxygenated water containing ionic impurities such as sulfate or chloride at the 0.1-ppm level. These results are consistent with the site blockage mechanism for different species that undergo cathodic reduction and control the rate of crack growth of the steel in the SCC tests. 39 refs., 5 figs., 4 tabs.