天然气管路导气球阀失效分析

摘要

目的 分析西部某气田天然气管路球阀发生开裂泄漏事故的原因.方法 对球阀的化学成分、断口、金相组织等进行检测分析.结果 球阀裂纹起源于阀体内表面,裂纹沿晶界扩展,晶界未发现贫铬现象,不存在晶间腐蚀;阀体材料存在沿晶铸造缺陷和枝晶露头,水淬激冷过程中形成沿晶微裂纹,承压状态下裂纹沿晶扩展;球阀螺纹根部最薄且应力集中,裂纹由内向外扩展,最终沿螺纹根部环向断裂,断口形貌为沿晶断裂.结论 导气球阀失效原因是螺纹根部存在应力集中和铸造阀体存在缺陷.在两者共同作用下,导致阀体承压状态下沿晶脆性断裂.%Objective To analyze causes of the leakage for rupture on ball valve of gas pipeline at a western natural gas field.Methods Chemical composition,fracture and microstructure of the ball valve were analyzed.Results The ball valve cracks originated from the body surface.The cracks extended along the grain boundary.Poor chromium phenomena were not detected in grain boundary and there was no intergranular corrosion.Dendrite and casting defects along grain boundary were found in the material.Micro-cracks formed along grain boundary in the process of water quenching.Cracks propagation was along the grain boundary under pressure.Thread root was the thinnest part and could produce stress concentration.Cracks extended outward and eventually ruptured along the thread root.The fracture morphology was the intergranular brittle fracture.Conclusion The reasons for ball valve failure are the stress concentration in thread root and defects in casting body.Under the effect of both,the intergranular brittle fracture occurs to the valve body under pressure condition.