LN206井中P110油管与潜油泵出口处连接泄油阀的丝扣仅使用了43 d就发生严重腐蚀, 对其进行了金相、化学分析和腐蚀电位测试。结果表明, 油管的金相组织无异常, 化学成分符合API Spec 5CT要求; 且油管与泄油阀连接的丝扣有损伤现象, 存在一定的缝隙, 高浓度的Cl-促进了腐蚀; 油管的铬含量与泄油阀的相差较大, 油管与泄油阀间的电位相差约110 mV, 电偶腐蚀加速丝扣处腐蚀。建议上扣时避免油管与泄油阀两者连接的丝扣发生损伤, 并在丝扣上涂抹质量好的螺纹脂将两者丝扣间的缝隙填满, 避免电位相差较大的异种材质直接连接。

Severe corrosion occurred at thread joint between submersible pump and spill valve of P110 in LN206 well tubing after 43 days service. The reason of the corrosion failure was studied by metallographic examination, chemical composition analysis, and electrochemical test. The results indicated that to the tubing material, no abnormal phase was found according to micro-morphology observation chemical composition met the requirement of API Spec 5CT. The surface damage was observed on the thread, so the corrosive medium go into the crevice at the damage area. The electrochemical test results show that the potential difference between oil well tubing and spill valve is approximately 110 mV. It is concluded that the corrosion was mainly caused by crevice corrosion, galvanic corrosion, and the high concentration of Cl- accelerated the corrosion process. It is suggested to avoid thread damage during joining the oil well tubing and spill valve. It is necessary thread grease to fully fill the crevice between oil well tubing and spill valve avoid the direct contact of dissimilar metals with significant potential difference.