深水油管轴向热变形及热应力分析

深水油气田开发过程中,油管处于内部高温流体与外部环空低温流体的大温差环境中,其引起的热变形和热应力会对油管柱的设计和使用造成影响。为此提出油管热变形模型,通过热变形试验,对轴向热变形量与线性热膨胀公式计算出的理论值进行对比分析,得出在一定温差范围内,线性热膨胀公式可以用于轴向热变形量的计算,但随着温差进一步扩大,轴向热变形规律变得模糊,其应用受到限制。同时,提出热应力的计算方法,对温差80℃下的N-80油管热应力分布进行分析,轴向应力远大于径向应力,即油管热变形以轴向热变形为主,内壁处热应力达到214.5 MPa,考虑到安全系数,热应力成为影响油管强度的重要因素。

Analysis of Thermal Deformation and Stress of Deepwater Tubing

Tubing lies in the environment of large temperature difference caused by internal high-temperature fluid and external annular low-temperature fluid in the development of deepwater gas and oil fields.The resultant thermal deformation and thermal stress will have effect on the design and use of tubing string.Therefore,the model of tubing thermal deformation was proposed.Through the thermal deformation test a comparative analysis of the axial thermal deformation and the theoretical value obtained by the linear thermal expansion formula was conducted.It is concluded that the formula can be used to calculate axial thermal deformation within a certain range of temperature difference.However,with the increase of temperature difference the law of axial thermal deformation becomes obscure and its application is thus limited.Meanwhile,the method to calculate thermal stress was also put forward.An analysis of the thermal stress of the N-80 tubing in the temperature difference of 80 ℃ was conducted.The axial stress was much greater than the radial stress.In other words the thermal deformation of tubing mainly belongs to axial thermal deformation.The thermal stress at the inner wall reaches 214.5 MPa.Considering the safety coefficient,thermal stress is a key factor to influence tubing strength.