某随钻测井仪钻铤接头内螺纹裂纹失效分析

Failure analysis of internal thread cracks in the drill collar joint of a logging tool while drilling

某随钻测井仪作业后发现钻铤接头内螺纹存在裂纹,造成该仪器无法作业;通过断口微观形貌分析、能谱分析、化学成分分析、硬度检验、金相组织分析来综合确定裂纹的产生机理并提出预防措施。分析结果表明:在腐蚀环境和复杂应力条件下,接头内螺纹裂纹始于齿顶侧壁的凹坑,开裂形式为穿晶解理断裂,兼具腐蚀疲劳断裂与应力腐蚀开裂;且钻铤材质沿晶界存在较多的沉淀,导致腐蚀敏感程度增加,也是裂纹产生机理之一。

After operating a logging tool while drilling,it was found that there were cracks in the internal threads of the drill collar joint,causing the tool to be unable to operate;By analyzing the microstructure of the fracture surface,energy spectrum analysis,chemical composition analysis,hardness testing,and metallographic structure analysis,the mechanism of crack formation is comprehensively determined and solutions are proposed.The analysis results indicate that under corrosive environments and complex stress conditions,the internal thread cracks in the joint originate from pits on the tooth top sidewall,and the cracking form is transgranular cleavage fracture,which combines corrosion fatigue fracture and stress corrosion cracking;One of the mechanisms behind crack formation is the increased corrosion sensitivity caused by the presence of numerous precipitates along grain boundaries in the material of drill collars.