含腐蚀缺陷X60油气管道剩余强度的分析

Analysis on Residual Strength of X60 Oil and Gas Pipeline Containing Corrosion Defect

利用ANSYS有限元分析软件,以X60油气管道长方形腐蚀缺陷为研究对象,首先考察其应力云图,其次通过改变腐蚀缺陷长度、缺陷深度、腐蚀位置及内压载荷,考察其对最大等效应力和剩余强度的影响。结果表明,含缺陷油气管道等效应力云图可以分为2个区域:远离缺陷区域和缺陷附近区域。远离缺陷区域应力基本均匀分布,此时应力为由内压载荷引起的薄膜应力;缺陷附近区域应力为不连续效应引起的不连续应力,呈现局部性和自限性。最大等效应力随内压载荷的增加可以分为2个阶段:屈服阶段和塑性强化阶段。当腐蚀缺陷长度系数一定时,随着腐蚀缺陷深度系数的增加,钢材的剩余强度呈现明显的递减趋势;当腐蚀缺陷深度系数一定时,随着缺陷长度系数的不断增加,剩余强度先减小后保持稳定,出现临界值0.2;内壁腐蚀比外壁腐蚀最大等效应力小,剩余强度大,安全性高。所得结论为钢材的安全评定以及最大程度提高有效利用率提供了支持。

Using ANSYS finite element analysis software,taking rectangular corrosion defect of X60 oil and gas pipeline as research object,in this paper,stress nephogram of rectangular corrosion defect is investigated firstly.Then effect of rectangular corrosion defect on the maximum equivalent stress and residual strength is investigated by changing length,depth,location and internal pressure load of corrosion defect.The results show that equivalent stress nephogram of defective oil and gas pipelines can be divided into two regions which are far from defect area and near defect area.Within far from defect area,stress distribution is basically uniform.At this time,stress is film stress caused by internal pressure load.In near defect area,stress is discontinuous stress caused by discontinuous effect,showing locality and self-limitation.With the increase of internal pressure load,residual strength of steel can be divided into two stages which are yield stage and plastic strengthening stage.When length coefficient of corrosion defect is constant,residual strength of steel decreases obviously with the increase of depth coefficient of corrosion defect.When depth coefficient of corrosion defect is constant,residual strength decreases first and then remains stable with the increase of length coefficient of corrosion defect.The threshold value is 0.2.The maximum equivalent stress of inner wall corrosion is smaller than that of outer wall corrosion,residual strength is larger and safety is higher.The conclusions could provide support for safety assessment and maximum effective utilization of steel.