D级抽油杆表面允许裂纹深度的估算

介绍了国内外七种Ｄ级抽油杆用钢的疲劳门坎值的测定。结合对抽油杆各特征部位半椭圆裂纹应力强度因子Ｋ的有限元计算，用断裂力学方法估算了各特征部位允许存在的裂纹尺寸。结果表明，允许裂纹深度α与使用应力σ之间存在有α＝Ａ／σ的关系。当抽油杆的抗拉强度符合ＡＰＩ规范１１Ｂ规定的σｂ＝７９３～９６５ＭＰａ时，七种材料的门坎值基本相同。当使用应力在疲劳极限附近处为３７２．６ＭＰａ时，抽油杆杆体表面存在有深度为０．１３～０．２７ｍｍ的裂纹，杆头锻方处存在有深度为０．６０～１．０２ｍｍ的裂纹，这些裂纹均不会扩展。

Estimation of allowable depth of surface cracks on Grade D sucker rods

Determination of the fatigue thresholds of seven kinds of Grade D sucker rod steel is described. According to the finite element calculation of the stress intensity factor of the semi-elliptical surface cracks on various characteristic parts of the sucker rod, the allowable size of cracks on these parts is estimated by the fracture mechanics method. The result of estimation shows that the relation between the allowable depth of crack a and the stress σis α=A/σn ; the thresholds of the seven materials are approximately identical when the tensile strength of the sucker rod σb is 793-965MPa; cracks 0. 13mm～0. 27mm in depth on the rod body and 0. 60mm～1. 02mm in depth on the square sections of the rod will not extend while the working stress near by the fatigue limit is 372. 6MPa.