油气管道在线焊接最大流速确定方法

Determination of peak flow rate of the media in oil-gas pipelines for in-service welding

以在线焊接实际工况为基础,采用有限元法进行输油气管道在线焊接流速与焊接热循环冷却速率t_(8/5)关系的模拟计算,系统研究各种因素对t_(8/5)的影响.在水介质计算和试验验证基础上,以管道壁厚和介质流速为主要影响因素,分析了不同壁厚和流速对t_(8/5)的影响,推导出三者之间的关系.结果表明,当壁厚大于12 mm后,内部介质流速的影响几乎消失,管道自身冷却能力占据主导地位.对于气体介质,需要考虑压力的影响,压力越大,t_(8/5)越小,且影响比较显著.不同材料在线焊接时允许的最大硬度与t_(8/5)密切相关,找出对应于临界硬度的t_(8/5)数值,即可按照获得的公式计算允许的最大介质流速.

Based on the actual working conditions of oilgas pipelines in-service welding,the simulating calculation of the relationship between the media flow rate and the cooling time t_(8/5) was carried out with finite element method,and the influence factors of t_(8/5) was systematically studied. Referring to the calculation and experimental verification results with the water medium,the influence of the media flow rate and the pipe wall thickness on t_(8/5) were analyzed and the relating formula among them was determined. The results showed that the action of the internal media flow rate on t_(8/5) could be negligible as the pipe wall thickness was greater than 12 mm. In that case,t_(8/5) was mainly controlled by the steel thermal conductivity. The gas pressure had a great impact on t_(8/5),the greater the pressure,the smaller t_(8/5) was. The allowable maximum hardness of difference pipeline steels for in-service welding is closely related with t_(8/5). The peak flow rate for the oil or gas medium was calculated with the gained formula while the value of t_(8/5) related to maximum hardness was determined.