Stress Corrosion Experimental Research Of 304 Austenitic Stainless Steel In NaOH+Cl^-+H₂O Complex Medium Condition

The chemical equipments which serve in complex medium of NaOH+Cl~-+H2O at high temperature often occur problem of stress corrosion cracking.The researches existing mainly focus on the single medium of concentration of NaOH or temperature,so that the conclusions existing have some limitation.In order to exploring the discipline of stress corrosion cracking in the complex medium,this article chose 304 stainless steel as research subject and used corrosion electrochemical experiment and SSRT as research method.This research made some exploration concerning stress corrosion of 304 stainless steel in NaOH+Cl~-+H2O complex medium environment and the major academic achievements are as follows:(1)The results of corrosion electrochemical experiment show that the corrosion mechanism of 304 stainless steel in NaOH+Cl~-+H2O complex medium tends to anodic dissolution and exists mechanism of competitive adsorption on the passive film between NaOH and Cl~-.(2)At the temperature of 100?,the stress corrosion sensitivity index of 304 stainless steel in complex medium of 10%NaOH+(100~1000)ppmCl~-is more than in the single medium of NaOH or Cl~-.It shows that the mechanism between NaOH and Cl~-is mutual promotion and competion effect.The SCC mechanism is dominated by Cl~-SCC in the complex medium condition of NaOH+Cl~-+H2O.(3)At the temperature of 200?,the sensitivity index of 304 in single medium of 10%NaOH and 20%NaOH are more than in the same concentration complex medium of NaOH+Cl~-+H2O.With increase of Cl~-concentration in NaOH+Cl~-+H2O complex medium,the sensitivity index presents an increase-reduce-increase trend.It shows that the mechanism between NaOH and Cl~-is mutual inhibition and competion effect.When NaOH concentration is 10% and 20% in NaOH+Cl~-+H2O complex medium,the SCC mechanism is dominated by NaOH SCC if Cl~-concentration is less than 200 ppm and dominated by Cl~-SCC if Clconcentration is more than 200 ppm.The critical conditions of SCC primary and secondary mechanism change are 10%NaOH+200ppmCl~-+H2O and 20%NaOH+200ppmCl~-+H2O.(4)In the complex corrosion condition of 5%NaOH+(100~1000)ppmCl~-+H2O at 230?,it exists mutual inhibition effect mechanism between NaOH and Cl~-in the process of SCC.The SCC mechanism in this condition is dominated by NaOH SCC.(5)The interaction math model of test medium parameters and susceptibility index F(A)by means of stepwise regression at 100? and 200? are as follows respectively: Y=16.5868-0.0208X2+0.0008X1X2-0.0041X1X3+0.000021X22(100?)and Y=12.6007+1.7225 X1-0.0462X2-0.0025X1X2+0.0001X22(200?).The parameters of NaOH and Cl~-have obvious influence on SCC and exists interaction mechanism.The research results can provide reference measures of preventing corrosion of chemical equipments manufactured by 304 stainless steel.