钻杆NC50内螺纹接头裂纹原因分析

Cause analysis on crack of NC50 box tool joint

吕拴录 袁鹏斌 姜涛 刘德英 宋顺平 李中全

LV Shuanlu YUAN Pengbin JIANG Tao LIU Deying SONG Shunping LI Zhongquan

中国石油大学，北京　102249 塔里木油田，新疆库尔勒　841000 上海海隆石油管材研究所，上海　200949 长庆石油勘探局钻井工程公司管具公司，宁夏银川　750006

Tarim Oil Field, Korla 841000, China China University of Petroleum, Beijing 102249, China Shanghai Hail Oil Tubular Goods Research Institute, Shanghai 200949, China

为推广应用斜坡吊卡台肩钻杆，对某井钻杆内螺纹接头直角吊卡台肩部位断裂和裂纹事故进行了详细调查研究，并对一根内螺纹接头钻杆进行了失效分析。失效分析内容主要包括裂纹宏观分析和微观分析，钻杆接头材料化学成分、力学性能和金相组织试验分析，钻杆在钻井过程中受力条件分析等。通过失效分析，认为钻杆接头为早期疲劳失效，钻杆内螺纹接头直角吊卡台肩部位产生早期疲劳断裂和裂纹的原因是该部位结构尺寸不合理，应力集中严重。在钻井过程中钻柱会承受交变的拉伸、扭转、弯曲、震动等疲劳载荷，很容易在应力集中严重的内螺纹接头直角吊卡台肩部位产生疲劳断裂和裂纹。要从根本上防止钻杆接头断裂，建议采用斜坡吊卡台肩钻杆。

This paper gives a thorough investigation on the accident of the drill pipe crack at square shoulder root of tool joint inorder to know the failure cause, and one sample of cracked tool joint is taken for failure analysis. Failure analysis comprises the macroand micro analysis, the experimental analysis of chemical composition, mechanical properties and microstructure of drill pipe joint, andthe analysis of load borne on drill pipe during drilling. It is reckoned that the early fatigue fracture of square shoulder root is caused bythe irrationality of the size of the root and the severe stress concentration at the square shoulder root of joint. Fatigue cracks easily occurat the square elevator shoulder root of joint, because the loads borne on drill string are tension, torsion, bend, and vibration that arecontinuously changed in drilling. It is suggested that taper elevator shoulder be used to prevent the crack of tool joint in essential.