CDZ 3150 KN吊卡卡页台肩根部裂纹分析

The Analysis of Crack Causation of Type CDZ 3150 KN Elevator Latch Shoulder Root

对在用吊卡进行解体检测,发现多数吊卡卡页上台肩根部存在裂纹,有CDZ 5” ×3150 KN和CDZ 5-1/2” ×3150 KN两种规格。首先对出现裂纹的吊卡卡页展开实验分析,从宏观形貌特征以及化学成分、机械力学性能,金相组织进行检测,发现卡页原材料符合标准要求,卡页台肩根部为疲劳裂纹。接着对吊卡的结构展开研究,建立三维模型,进行有限元分析,同时根据API 8C规定对吊卡进行强度分析,分别从等效应力和极限强度方面进行理论计算。对有限元分析结果和理论计算结果进行对比,发现卡页台肩根部圆角半径较小时,虽然有限元分析结果满足API8C按照极限强度分析的最大允许应力,但是考虑到出厂载荷试验和现场工况等,只有圆角半径不小于R5时的有限元分析结果小于API计算的最大允许应力。建议采用R5以上的圆角半径,以及在不影响活页开合情况下增加卡页厚度,以提高卡页的抗疲劳性能和使用寿命,确保使用安全。

When disassembled the CDZ dill pipe elevator for detection, it was found that most of the elevator latch had cracks at the shoulder root of the upper stage. There were two specifications: CDZ 5” ×3150 KN and CDZ 5-1/2” ×3150 KN. Firstly, the cracked elevator latches were analyzed experi-mentally. From the macro-morphological characteristics, chemical composition, mechanical proper-ties and metallographic structure, it was found that the raw materials of the elevator latch met the requirements of current standards, and the crack on the shoulder root at the upper stage of the elevator latch was fatigue crack. Secondly, the structure of the elevator was studied, three-dimen- sional model was established;finite element analysis was carried out;and the strength of the ele-vator was analyzed according to API 8C, and theoretical calculation was carried out respectively from the aspects of equivalent stress and ultimate strength. Comparing the finite element analysis results with the theoretical calculation results, it was found that when the arc radius of the shoulder is small, the finite element analysis results satisfy the maximum allowable stress of API 8C ac-cording to the ultimate strength analysis, but considering the factory load test and working condi-tions, only when the arc radius is not less than R5, the finite element analysis results are less than the maximum allowable stress calculated by API. It is suggested to use arc radius above R5 and also increase the latch thickness without affecting elevator door opening and closing, so as to improve the fatigue resistance and service life of the latch and ensure the safety of the use of the elevator in ultra-deep wells.