H2S和CO2分压及Cl-浓度对L360QCS钢腐蚀行为的影响

通过高温高压反应釜模拟普光气田集输环境,研究H2S和CO2分压及Cl-浓度对普光气田用集输管线钢L360QCS钢腐蚀行为的影响。采用失重法测试腐蚀速率,用四点弯曲法进行应力腐蚀试验,结合宏观形貌观察和扫描电镜(SEM)微观观察及能谱(EDS)分析,进行了综合研究。在H2S和CO2分压比固定的情况下,随着H2S压力升高,腐蚀速率先降后升。压力较低时,L360QCS应力腐蚀试样表面均出现不同程度的氢鼓泡,当压力升高时,氢鼓泡减少或者消失。腐蚀速率随着Cl-浓度的升高而增大,达到临界值后,腐蚀速率随着Cl-浓度的升高而降低;在低浓度条件下,Cl-浓度的增加会促进点蚀的发生,进而诱发裂纹的产生;而当Cl-浓度增加到临界值时,腐蚀产物的沉积可以抑制点蚀的生成,从而使材料的应力腐蚀开裂敏感性降低。

Effect of H2S/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.