基于等效缺陷尺寸在役焊接安全性评价研究

采用有限元模拟软件SYSWELD对X70管线钢在役焊接瞬时温度场进行模拟,综合考虑焊接熔池尺寸及高温区金属强度损失,运用强度路径积分法对焊接熔池进行等效。将等效熔池看作是体积型缺陷,基于等效缺陷尺寸对在役焊接安全工作压力进行计算,进而对输气管道在役焊接安全性进行评价。结果表明:随着壁厚增大,安全工作压力增大,安全性增强;管径增大,安全工作压力减小,安全性降低,等效缺陷长度修正因子可削弱这种影响;气体介质条件下安全工作压力与饱和水介质相比较小,同时气体压力、流速对安全工作压力影响较小,在一定壁厚下用常规空气冷却条件下的等效缺陷尺寸进行安全性评价是保守的。

Safety evaluation of service welding based on equivalent defect size

The instantaneous temperature field of the X70 pipeline steel during in-service welding was simulated by the FEM software SYSWELD. Considering the size of the welding molten pool and the metal strength loss in high temperature areas, the equivalent size of the welding molten pool was calculated using the strength path integral method. The equivalent welding molten pool was viewed as a volume type defect, then the safety working pressure of the in-service welding was calculated based on the equivalent defect size, and the safety of gas pipelines in-service welding is evaluated. The results show that the safety working pressure increases with the wall thickness increasing, ie. it is more safe. The safety working pressure decreases with the pipe diameter increasing, but the length correction coefficient of the equivalent defect weakens this effect. The safety working pressure under the gas medium condition is smaller than that under the saturated aqueous medium condition. It is also found that the gas medium pressure and flow velocity have little impact on the safety working pressure. For a certain wall thickness, it ''s conservative to use the equivalent defect size under the conventional air cooling condition to perform safety evaluations.