825合金在含单质硫高温高酸性环境中的局部腐蚀行为

Local Corrosion Behavior of 825 Alloy in Elemental Sulfur-Containing High Temperature and High Acid Environment

在132℃、H2S分压4.8MPa、CO_(2)分压1.6MPa、氯离子质量浓度42750mg·L^(-1)的气田模拟地层水中,通过腐蚀挂片试验研究了825合金在含单质硫(每升地层水中包裹合金的单质硫质量为10g)与不含单质硫条件下的局部腐蚀行为。结果表明:在不含单质硫条件下825合金几乎不发生腐蚀,腐蚀6d时的腐蚀速率仅为0.0077mm·a^(-1);添加单质硫腐蚀3d时腐蚀速率达到0.0552mm·a^(-1),合金发生了严重的局部腐蚀,随腐蚀时间的延长,合金表面局部腐蚀坑面积、腐蚀坑最大深度和腐蚀速率增大。在不含单质硫条件下合金表面腐蚀产物极少,主要为FeCO_(3),在含单质硫条件下,随着腐蚀时间的延长,表面腐蚀产物增多,主要为FeCO_(3)与FeS;单质硫在高温下发生歧化反应产生H^(+)和S^(2-),使825合金表面腐蚀产物膜破裂,从而加剧了局部腐蚀。

The local corrosion behavior of 825 alloy in simulated formation water of gas field at 132℃ with H2S partial pressure of 4.8 MPa,CO_(2) partial pressure of 1.6 MPa,and chloride ion mass concentration of 42750 mg·L^(−1) under elemental sulfur-containing condition(mass of elemental sulfur coated alloy in per liter formation water was 10 g)and under elemental sulfur-free condition was investigated by corrosion coupon tests.The results show that under the elemental sulfur-free condition,825 alloy almost did not corrode,and the corrosion rate was only 0.0077 mm·a^(−1) during corrosion for 6 d.The corrosion rate reached 0.0552 mm·a^(−1) duing corrosion for 3 d under elemental sulfur-containing condition,showing the serious local corrosion of the alloy.With the increase of the corrosion time,the area of local corrosion pits on the alloy surface,the maximum depth of corrosion pits and the corrosion rate increased.The corrosion products of the alloy under the elemental sulfur-free condition were very few and were mainly composed of FeCO3.Under the elemental sulfur-containing condition,the surface corrosion products increased in amount with the corrosion time and were mainly composed of FeCO_(3) and FeS.The elemental sulfur underwent disproportionation reaction at high temperature,producing H^(+)and S^(2−),making 825 alloy corrosion product film rupture,therefore promoting the local corrosion.