特殊扣钢管的疲劳理论、试验与应用

Fatigue Theory,Tests and Application of Premium Thread Steel Pipes

为了促进特殊扣钢管抗疲劳性能的进一步提升,从特殊扣钢管管体材料的疲劳、螺纹连接的疲劳、螺纹连接的设计等方面进行了研究。分析了循环载荷作用下特殊扣钢管疲劳产生的主要原因;以法国V&M公司和阿根廷Tenaris公司等国外主流抗疲劳特殊扣产品为例,阐述了螺纹设计时摩擦系数、螺距、锥度和应力释放结构对疲劳的影响;介绍了研究特殊扣钢管疲劳问题的试验装置及测取S-N曲线的基本问题,重点讲述了共振型全尺寸疲劳评价试验装置的试验原理。研究结果表明,影响螺纹结构套管疲劳强度的最主要因素是应力集中系数(SCF),螺纹结构往往在公端最后一圈螺纹LET处应力最大,应力集中系数也较大。因此,螺纹结构套管在结构设计上应尽量采用圆滑过渡来降低应力集中系数,母端外侧应考虑抗弯曲机构;可适当降低母端的壁厚、提高螺纹结构的加工精度,在设计上尽量考虑应力释放部分及去除残余应力工艺的使用,从而提高特殊扣钢管的抗疲劳性能。

In order to promote the further improvement of the anti-fatigue performance of premium thread steel pipe,in this article,the fatigue performance of pipe body material was researched,as well as the fatigue and design of threaded connections. The main reason of fatigue of premium thread steel pipe was analyzed. Take anti-fatigue premium thread products of French VM company and Argentine Tenaris company for instance,the influence of frictional coefficient,pitch, taper and stress releasing structure on fatigue at design time were expounded,the basic issues of fatigue test machine and S-N curve measure were introduced,and the test principles of resonance full-scale test apparatus of fatigue evaluation were focused on.According to the research results,the major factor influencing thread casing fatigue strength was stress concentration factor（SCF） which had a larger value in LET of pin with the maximum stress. Therefore,smooth transition was used to reduce SCF in thread casing structure design,resistance to deflection structure should be considered outside female ends;wall thickness of female ends should be reduced,machining accuracy of thread structure should be improved,stress releasing and residual stress removal should be used to improve the fatigue performance of premium connection of steel pipe.