为查明某井139.7 mm加重钻杆外螺纹接头的断裂原因,对断口进行了宏观和微观分析,对材料进行了化学成分分析、力学性能试验和金相分析,并进行了有限元分析等.结果表明:加重钻杆断裂属于腐蚀疲劳断裂;断裂主要原因是加重钻杆接头内径大于标准规定值,降低了加重钻杆外螺纹接头断裂扭矩和抗拉载荷,在疲劳载荷与腐蚀介质作用下,腐蚀疲劳裂纹首先在加重钻杆外螺纹接头危险截面部位螺纹牙底萌生,随后在载荷作用下裂纹不断扩展,进一步降低了接头的强度,最终发生了断裂事故.

For investigating the failure causes of pin joint fracture of a 139.7 mm heavy weight drill pipe,macro and micro analyses of the fracture surface were carried out.And the material chemical composition analysis,mechanical property test,metallography and finite element analysis were performed.The results show that the pin joint fracture of heavy weight drill pipe was corrosion fatigue failure.The tensile strength and torsion strength of the heavy weight drill pipe pin joint were reduced because its inner diameter was bigger than that specified in the standard,which led to the fracture.Under fatigue load and corrosion medium,corrosion fatigue crack appeared first at the bottom of thread which was the dangerous section part of the pin joint.Then the crack grew constantly under the loading and further reduced the joint strength,which led to final fracture.