Slip-dissolution model of stress corrosion crack growth andpossibilities of its application for evaluation of stress corrosioncracking susceptibility of duplex stainless steels in hydrogensulfide-chloride environments at 120℃

摘要

Results are summarized of the feasibility of using slip-dissolution model of stressrncorrosion crack growth for the evaluation of stress corrosion cracking (SCC)rnsusceptibility of duplex stainless steels in hydrogen sulfide-chloride environments atrn120℃.rnFirst a brief note is presented about the historical background of the concept ofrndiscussion of SCC results received in the constant extension rate test (CERT) ofrnstainless steels in terms of phenomenological model that incorporates a slipdissolutionrnmechanism and elastic-plastic fracture mechanics. Introducing of thernaverage near crack-tip strain rate, T e& and average crack growth rate av a& as quantitiesrnmeasurable in CERT test has allowed a comparison to existing theoretical model ofrnFord. This idea has been used in our slow strain rate tests (SSRT) of duplex stainlessrnsteels (DSS) in hydrogen sulfide-chloride environments at 120℃. It is shown thatrnexperimental values of T e& and av a& determined in SSRT experiments for several duplexrnstainless steels in 20%NaCl-H2S (pH=4) at 120℃ can be used for calculation of in putrnparameters of the slip-dissolution model for stress-corrosion cracking. It has onlyrnbeen possible due to exact analysis of stress-vs.-strain curves and due to adoptingrnthe supposed value for fracture-strain of oxide film at crack tip, f. Values of raternconstant for the bare surface reaction at the crack tip, k and current decay exponentrnat the crack tip, m estimated for various partial pressures H2S (ppH2S) made possiblernthe evaluation of changing electrochemical conditions under which cracks occur inrnvarious DSS during mentioned SSRT experiments.