The Experimental Investigation Of Stress Corrosion For 16MnR Steel In Complex Solution Containing Carbonate And Hydrogen Sulfide

Wide and in-depth researches have been carried out on the stress corrosion in the environment of single corrosive medium like wet hydrogen sulfide,etc.and a great number of research results were reported.But in actual production there is a great variety of corrosive media and the influential factors are complicated.Especially in the petrochemical industry,etc., in which corrosive media involve hydrogen sulfide,chloride ions,carbonate,nitrate,etc., therefore,in general case there will exist several media at the same time.Based on the corrosion type of H₂S-CO₂-H₂O,CO-CO₂-CO₃^2--H₂O,H₂S-CO₃^2--H₂O etc.,which may be present in petrochemical production units,in this paper,the effect of temperature and concentration of carbonate and hydrogen sulfide on SCC of 16MnR steel is investigated with reference to actual operating conditions of decarburization system for hydrogen-making plant through the slow strain rate test(SSRT) and WOL,wedge opening loading(WOL) test in the lab.Through these investigations,the sensitivity of SCC and the crack propagation rate of base metal and heat affected zone of 16MnR steel in above solutions are mastered,which provide a basis for corrosion protection and safety assessment of in-service equipment and is of important significance for guiding safe production.The main research works and findings in this paper are summarized as follows:(1) The sensitivity of base metal and heat affected zone of 16MnR steel to stress corrosion is not significant in the complex environment of media adopted in this paper,such as Na₂CO₃ and H₂S,the fracture morphology is dominated by dimples.(2) Under complex environment of media such as 350 ppm H₂S + 5%Na₂CO₃,The sensitivity of base metal and heat affected zone of 16MnR steel to stress corrosion at 57.5℃is higher than that at normal temperature.(3) At normal temperature,the sensitivity of 16MnR steel to stress corrosion under the environment of 200 ppm H₂S is higher than that under the environment of 200 ppm H₂S +25% Na₂CO₃.(4) Under the conditions of this experimental research,the stress corrosion sensitivities of base metal and heat affected zone are close.(5) With reference to the uniform design method,WOL tests are carried out under the complex medium environment of different temperatures(25℃,57.5℃and 90℃),different concentrations of H₂S(50 ppm,200 ppm and 350 ppm) and different concentrations of Na₂CO3 (5%,15%and 25%),and the stress corrosion crack propagation rate of 16MnR steel in the above solutions falls within the range of 0.33×10^-8 mm/s～4.31×10^-8 mm/s.