铝合金钻杆冲蚀磨损原因分析

Cause Analysis on Erosive Wear of Aluminum Alloy Drill Pipe

Φ147 mm钢接箍D16T铝合金钻杆在某油田的油气井中使用时发生了冲蚀磨损失效。为了确定其失效的原因,对该铝合金钻杆的冲蚀磨损形貌进行了宏观和微观分析,对其接头的结构尺寸进行了测量分析,对其管体材料的化学成分、力学性能和金相组织进行了试验分析。结果表明,该铝合金钻杆管体材料的化学成分符合ISO 209:2007标准的要求,但其拉伸性能不符合ISO 15546:2007标准要求。钻杆钢接箍与铝合金管体外螺纹接头上扣连接后,其管体外螺纹端部与接箍内表面的交界部位存在凸起台阶结构,因而在使用时钻井液在凸起台阶部位形成了紊流,冲蚀磨损了凸起的钻杆外螺纹端部,因此该铝合金钻杆接箍内的凸起台阶结构是冲蚀磨损失效的主要原因。钻杆材料的强度越低,冲蚀磨损的速度越快,即钻杆管体材料的抗拉强度和屈服强度低于标准的要求是冲蚀磨损失效的次要原因。建议在设计加工时,钻杆管体外螺纹接头与钢接箍连接后其接头内表面交界部位应保持平滑过渡,即不应有凸起台阶;另外,应采用高强度的铝合金材料制造钻杆管体。

The Φ147 mm D16T aluminum alloy drill pipe with steel coupling failed due to erosive wear during service in an oil and gas well in a certain oilfield.In order to find out the cause of the failure,the macro and micro erosive wear morphology of the aluminum alloy drill pipe was analyzed,the structural dimension of the joint was measured and analyzed,and the chemical composition,mechanical property and metallographic structure of the pipe body material was tested or investigated.It is shown that the chemical composition of the aluminum alloy drill pipe body material is in accordance with ISO 209:2007 standard,but the tensile properties of the pipe body material is not qualified according to ISO 15546:2007.There is a protrusion step at the junction between pin end and the inner surface of the coupling,where the pin shoulder is eroded by turbulent drilling fluid,and then erosive wear failure takes place.Therefore,the first cause of erosive wear failure is the structure of protrusion step at the connection.Additionally,the second cause of failure is related to insufficient strength of the drill pipe body.It is suggested to keep a smooth transition and no protrusion step at the junction of the inner surface of the joint after the pin thread joint of the drill pipe is connected to the steel coupling during its design and processing.furthermore,high-strength aluminum alloy materials should be used to manufacture drill pipe bodies.