局部内缺陷套管剩余抗扭强度分析

关于含缺陷套管抗扭强度的研究较少,基于弹性失效准则分析缺陷套管强度又较为保守。为此,基于材料塑性破坏准则,运用非线性有限元方法并结合正交试验设计,对局部内缺陷套管剩余抗扭强度进行分析,探究了缺陷长度、宽度、深度、套管外径和径厚比等参数对套管剩余抗扭强度的影响规律。研究结果表明:随缺陷深度增加,抗扭强度呈线性大幅度降低;当缺陷长度小于临界长度时,抗扭强度随长度增加而增大,超过临界长度后,抗扭强度随长度增加而降低;当缺陷宽度小于临界宽度时,抗扭强度随宽度增加而增大,超过临界宽度后,抗扭强度随宽度增加而降低;随套管径厚比增加,无因次抗扭强度近似呈线性减小。缺陷深度是影响抗扭强度最重要的因素,缺陷宽度次之,缺陷长度和套管径厚比有一定的影响,而套管外径的影响可以忽略。在此基础上,拟合了抗扭强度计算公式,公式预测值与有限元分析结果误差较小,可为工程上局部内缺陷套管强度评价提供参考。

Analysis of Residual Torsional Strength of Casing with Partial Internal Defects

There are few studies on the torsional strength of casings with defects.The strength analysis of casing defects based on the elastic failure criterion is conservative.To address the issue,based on the material plastic failure criterion,the nonlinear finite element method is combined with the orthogonal experimental design to analyze the residual torsional strength of the casing with partial inner defect.The influences of parameters such as the defect length,defect width,defect depth,casing outer diameter,diameter-thickness ratio on the residual torsional strength of the casing are investigated.The results show that the torsional strength decreases linearly with the increase of defect depth.When the defect length is less than the critical length,the torsional strength increases with the defect length.After exceeding the critical length,the torsional strength decreases with the defect length.The defect width has a similar influence trend to the defect length.With the increase of the casing diameter-thickness ratio,the dimensionless torsional strength is approximately linearly reduced.The defect depth,followed by the defect width,is the most important factor affecting the torsional strength.The defect length and the casing diameter-to-thickness ratio have a certain influence.The influence of the casing outer diameter can be neglected.On this basis,the formula for calculating the torsional strength is fitted.The error between the formula prediction value and the finite element analysis result is small,which can provide references for the strength evaluation of casing with partial inner defect.