柴油机尾气欠平衡钻井中压缩机阀片失效机理

Failure mechanism of compressor valve plates in diesel tail gas underbalanced drilling

柴油机尾气钻井属于气基欠平衡钻井,尾气中含有CO2、O2等腐蚀介质以及炭黑等固体微粒,在实际工况下容易导致压缩机阀片开裂失效。通过对失效阀片断口的宏观分析和表面分析以及模拟尾气环境中的腐蚀试验,认为阀片失效是由于长期工作在含CO2、O2的潮湿酸性环境中引起阀片的均匀腐蚀和点腐蚀,高速气流夹杂固体炭黑等颗粒的冲蚀加剧了这种腐蚀,导致阀片在孔蚀薄弱部位开裂,此外由于尾气中的杂质硫可引起钢材的硫化物应力腐蚀开裂,随着阀片的反复运转和上述因素的共同作用,阀片表面裂纹不断扩展和加深,最后引起阀片断裂失效。根据现场经验和阀片失效机理提出了减缓阀片失效的预防措施。

Diesel tail gas drilling belongs to gas-based underbalanced drilling. Due to complex composition, especially containing carbon dioxide, oxygen, and soot solid particles, diesel tail gas can give rise fracture failure to air compressor valve plates. Through macroscopical analysis, surface analysis and simulating corrosion test of failure valve plates, It concludes that valve plate failure originates from uniform corrosion and pitting corrosion for long term working in wet environment of containing carbon dioxide and oxygen, and high speed airflow carrying soot solid particulates accelerates corrosiveness, which resulting in crack initiating in weak location of materials. Furthermore impurity sulfur in tail gas may induce sulfide stress corrosion cracking, with valve plates repeating movement, above factors common action leading crack propagating and deepening, in the end resulting in rupture failure of valve plates. Combining field experiment and failure mechanism, prevention measures are put forward hereinafter to reduce valve plates failure.