158.8mm钻铤裂纹原因分析

对158．8mm钻铤裂纹事故进行了调查研究。对裂纹形貌用扫描电镜和金相显微镜进行了全面观察分析，认为钻铤裂纹属于早期疲劳破坏。对钻铤裂纹部位的结构形状和材质进一步试验分析结果，认为裂纹正好处在内螺纹最后消失部位，该部位存在严重的应力集中。钻铤在使用过程中，从内表面应力集中严重部位首先萌生裂纹，最后扩展形成了穿透的裂纹。

Analysis of the Causes of the Crack in the 158.8mm Drill Collar

An investigation is made into a crack in the 158.8mm drill collar.A thorough examination of the crack appearance by using SEM and metallograph indicates that the damage was caused by early fatigue.A further test of the structure and material of the cracked part shows that the crack is just at the last runout of internal thread,where stress is highly concentrated.During the service of the drill collar,a slight crack first appeared in the inner surfacce with high stress and then it deepened through the wall of the drill collar.