在模拟气井油套管环空环境中(溶有CO2和H2S的地层水), 采用电化学试验、腐蚀失重法和腐蚀形貌观察等方法对17-4不锈钢和C110套管钢间的电偶腐蚀进行了研究。结果表明: 17-4不锈钢和C110钢发生了严重的电偶腐蚀; C110钢的腐蚀产物膜中铁/硫原子比比单独腐蚀时增大, 其保护性下降, C110钢作为阳极被加速腐蚀, 其电偶腐蚀系数达到2.51, 腐蚀速率为0.642 0 mm·a-1, 电偶电流受两种钢的电位差所控制; 当加入环空保护液后, 两种钢间的电位差明显减小, 它们的电偶腐蚀得到有效抑制, C110钢的腐蚀速率降低至0.042 3 mm·a-1。

The corrosion of galvanic couple composed of 17-4 stainless steel and C110 steel was investigated by methods of electrochemical testing, weight loss testing of corrosion, corrosion morphology observasion in simulated casing annulus environment in gas wells where CO2 and H2S dissolved in formation water. The results show that serious galvanic corrosion was found when 17-4 stainless steel coupled with C110 steel. The atomic ratio of Fe to S in galvanic corrosion scale on the surface of C110 steel increased, compared to separate corrosion of C110 steel, leading to the dropping of corrosion resistance of the corrosion scale, and then the C110 steel as anodic material in the couple accelerated the corrosion with the galvanic corrosion factor of 2.51 and the corrosion rate of 0.642 0 mm·a-1. The galvanic current was controlled by the potential difference between 17-4 stainless steel and C110 steel. The potential difference between the two metals in simulated formation water plus annulus protection fluid decreased drastically, and the galvanic corrosion was mitigated markedly. The corrosion rate of C110 steel reduced to 0.042 3 mm·a-1.