Effect of H₂S和CO₂ 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.