Effect of H_2S/CO_2 Pressure and Cl~- Concentration on Corrosion Behavior of L360QCS Steel

The influences of partial pressure of H2S and CO2 and concentration of Cl-on corrosion behavior of L360QCS steel as gathering and transportation pipeline in sour environment simulating Puguang natural gas field were investigated in an autoclave.Weight-loss method and four point bending method were used to investigate the corrosion rate and SSCC(sulfide stress corrosion cracking) susceptibility respectively.Microscopy,SEM and EDS were employed for studying the surface morphology,microstructure and composition of the corrosion products.At the same H2S/CO2,corrosion rate of L360QCS decreased at the beginning and increased later with the increase of sour gas pressure.Hydrogen blister was observed at a low pressure.When the pressure increased,the hydrogen blister was depressed and finally disappeared.There was a critical value of Cl-.When Cl-concentration was less than its critical value,the corrosion rate increased with increasing the Cl-concentration and the Cl-also induced pit corrosion and then SCC.Contrarily,when Cl-concentration was greater than the critical value,the deposition of corrosion products would improve the pitting corrosion resistance and thus reduce SCC susceptibility.