Slip-dissolution model of stress corrosion crack growth and possibilities of its application for evaluation of stress corrosion cracking susceptibility of duplex stainless steels in hydrogen sulfide-chloride environments at 120°C

Abstract

Results are summarized of the feasibility of using slip-dissolution model of stress corrosion crack growth for the evaluation of stress corrosion cracking (SCC) susceptibility of duplex stainless steels in hydrogen sulfide-chloride environments at 120°C. First a brief note is presented about the historical background of the concept of discussion of SCC results received in the constant extension rate test (CERT) of stainless steels in terms of phenomenological model that incorporates a slip-dissolution mechanism and elastic-plastic fracture mechanics, introducing of the average near crack-tip strain rate, ε̄T and average crack growth rate αav as quantities measurable in CERT test has allowed a comparison to existing theoretical model of Ford. This idea has been used in our slow strain rate tests (SSRT) of duplex stainless steels (DSS) in hydrogen sulfide-chloride environments at 120°C. It is shown that experimental values of ε̄T and αav determined in SSRT experiments for several duplex stainless steels in 20%NaCl-H2S (pH=4) at 120°C can be used for calculation of input parameters of the slip-dissolution model for stress-corrosion cracking. It has only been possible due to exact analysis of stress-vs.-strain curves and the determination of supposed value for fracture-strain of oxide film at crack tip, f. (Values of rate constant for the bare surface reaction at the crack tip, k and current decay exponent at the crack tip, m estimated for various partial pressures H2S (ppH2S) made possible the evaluation of changing electrochemical conditions under which cracks occur in various DSS during mentioned SSRT experiments