Stress Corrosion Experimental Research Of 316L Stainless Steel In Cl^- And CH₃COOH And H₂O Medium Condition

The corrosion cracking of stainless steel pipeline in EOEG multi effect evaporation system often occurs with the increase of service life.Most of the existing studies mainly focus on the single factor of Cl^-concentration or temperature and so on,and the conclusion often has some limitations.In order to explore the effect of trace Cl^-,CH₃COOH and temperature on the stress corrosion susceptibility of 316L stainless steel,the SCC problem in Cl^-+CH₃COOH+H₂O complex medium environment was studied by means of electrochemical test,slow strain rate tensile test and XPS energy spectrum analysis,and the main conclusions are as follows:?1?The test of potentialdynamic polarization curves shows that under the condition of75?,when the concentration of Cl^-is at 0-500ppm,the pitting potential of 316L stainless steel moves in a negative direction with the increase of Cl^-concentration,but the addition of acetic acid has a certain inhibitory effect on pitting corrosion.The EIS shows that with the increase of Cl^-concentration,the stability of passivation film decreases,but the addition of acetic acid increases the passivation film resistance.?2?The SSRT text shows that at the temperature of 125?,the corrosion sensitivity of316L stainless steel increases rapidly when the concentration of Cl^-reaches 2000ppm,and the second cracks appear in the fracture.With a addition of 500ppm CH₃COOH,the rate of uniform corrosion accelerates and the passive film formed on the surface of stainless steel inhibites the Cl^-SCC.With the increase of Cl^-concentration,the passive film is broke.However the leading mechanism is not changed.With a addition of 2000ppm CH₃COOH,the stress corrosion sensitivity decreases with the increase of Cl^-concentration.Combined with XPS analysis it is found that the destruction effect of Cl^-on passive film is weakened,and the effect of uniform corrosion increases.?3?In a single medium solution of Cl^-at 175?,with the increase of Cl^-concentration the stress corrosion sensitivity change little,which indicates that the increase of temperature inhibits the increase of corrosion sensitivity.After the addition of acetic acid,the stress corrosion sensitivity turns to zero.And uniform corrosion is dominant in the process of corrosion.?4?The interaction model between the stress corrosion sensitivity and the medium factors of 316L stainless steel in Cl^-+CH₃COOH+H₂O medium is established by stepwise regression method as follows:Y=6.0394+0.0091X₁-0.0064X₂+4.5?10^-6X₁ X₂-1.5810^-5X₁ X₃+2.79?10^-6X₂²-0.00025X₃²,it has a interaction between Cl^-and CH3COOH.?5?The results show that the cracking leading mechanism of austenitic stainless steel equipment and pipes is Cl^-SCC in the EOEG multi effect evaporation system.The acetic acid in the medium has a certain inhibitory effect on SCC,but can not avoid it.At the same time,it is necessary to control the concentration of Cl^-in the medium or upgrade the material to prevent the failure from SCC.In this paper,the corrosion behavior of 316L stainless steel in the medium of Cl^-+CH₃COOH+H₂O was studied and it is found that the corrosion mechanism in this solution system is anodic dissolution.The research results can provide reference measures for corrosion protection technology of EOEG equipment manufactured by 316L stainless steel.