石油套管淬火过程中残余应力场的数值模拟

Numerical simulation of residual stress field in an oil casing during quenching process

为降低P110级石油套管淬火冷却过程中的内应力,提出"水淬—空冷—水淬"的优化冷却方式,并利用有限元方法对冷却过程中温度、应力场的变化规律和分布状态进行了模拟.模拟结果表明:冷却至7.5s出水时,横截面上最大温差为104℃,空冷结束时断面温度均匀;再次水冷的最大温差为80℃,与7.5s时相比,温差降低了24℃.对于应力,在最初的水冷阶段,从开始到2.5s,切向应力增大,2.5～5.5s,切向应力降低,冷却至5.5s时发生组织转变,此后热应力和组织应力共存,切向应力随冷却进行迅速升高,并在7.5s时达到最大,为563MPa;出水空冷阶段,热应力减小,组织应力消失,13s空冷结束时切向应力分布较均匀,为-11～27MPa;再次入水冷却至13.6s,切向应力再次达到最大,为451MPa,比7.5s时的563MPa降低了112MPa,达到了优化冷却工艺的目的.

In order to reduce the internal stress of a P110 oil casing during quenching,an optimized cooling process ＂water-quenching→air-cooling→water-quenching＂ was proposed.The change and distribution of temperature and stress field of the casing during cooling process were simulated by finite element method.The simulated results show that the maximum temperature difference is 104℃ after water-quenching for 7.5s,and the distribution of cross-section temperature is uniform at the end of air-cooling.When the casing is quenched by water again,the temperature difference is 80℃,which is 24℃ lower than that of 7.5s.For the stress,at the first water-quenching stage,the tangential stress increases from the beginning to 2.5s and then decreases form 2.5 to 5.5s.At 5.5s phase transformation occurs.After that there are both thermal stress and structural stress in the casing,hence the tangential stress increases sharply and peaks at 563MPa at 7.5s.At the air-cooling stage,as the thermal stress decreases and the structural stress disappears,the distribution of tangential stress becomes uniform and levels off at-11 to 27MPa at the end.When the casing is quenched in water again,the tangential stress increases and reaches the peak again at 451MPa at 13.6s,which is 112MPa lower than 563MPa at 7.5s,thereby optimizing the cooling process.