连续油管配套42CrMo钢挠性连接器断裂原因

Reasons for fracture of matching 42CrMo steel flexible connector for continuous oil pipe

某油田连续油管配套挠性连接器出现断裂现象。采用宏观观察、化学成分分析、扫描电镜分析、金相检验、硬度测试等方法对挠性连接器断裂原因进行分析。结果表明:挠性连接器的断裂性质为疲劳断裂,挠性连接器结构中过渡圆角半径设计偏小、车削加工切削参数设置不合理、母材中存在形状不一的微孔洞缺陷,使材料产生应力集中;挠性连接器热处理工艺参数设计不合理,导致其硬度偏大,塑性变形能力较小,促进了疲劳裂纹的扩展;在低周疲劳载荷及交变载荷的作用下,应力集中处萌生微裂纹,裂纹不断扩展,最终导致挠性连接器断裂。

The flexible connector of the continuous oil pipe in a certain oilfield fractured.The reasons for the fracture of flexible connectors were analyzed using macroscopic observation,chemical composition analysis,scanning electron microscopy analysis,metallographic examination and hardness testing.The results show that the fracture property of the flexible connector was fatigue fracture.The design of the transition fillet radius in the flexible connector structure was too small,the cutting parameters for turning were not reasonable,and there were micro hole defects with different shapes in the base material,which caused stress concentration in the material.The unreasonable design of heat treatment process parameters for flexible connectors led to excessive hardness and low plastic deformation capacity,which promoted the propagation of fatigue cracks.Under the action of low cycle fatigue load and alternating load,microcracks initiated at the stress concentration point,and the cracks continued to propagate,ultimately led to the fracture of the flexible connector.