长输天然气管道焊口带磁的产生原因及消磁方法

Reasons for the occurrence of magnetic field on pipeline craters and the relavant demagnetization methods

在天然气长输管道停气换管作业中,常常会遇到因管道带磁而无法正常施焊的情况,既影响焊口质量,又耽误施工时间。为此,分析归纳总结出了导致管道焊口带磁的原因:①管道检测工艺的影响;②制管工艺的影响;③环境的影响;④管道安装过程的影响;⑤管内介质的影响。进而分析了管道焊口带磁对管道焊接的影响:根焊时会出现焊接电弧,产生磁偏吹,干扰电弧稳定性,容易产生焊接缺陷。最后从管道消磁的基本理论入手,结合管道消磁工作的实际经验,提出了5种管道消磁方法:①绕线组法;②采用专业消磁设备法;③升温法;④搭桥法;⑤清洗法。研究成果对类似情况有较好的指导作用。

During the pipe displacement work with the cut-off of gas supply in long-distance gas pipelines,welding operation can not be normally performed due to the occurrence of the magnetic field on the pipe,which affects not only the crater quality,but also the construction schedule.This paper first presents the main reasons for the magnetic field on the pipe from the following aspects: pipeline detection technique,pipeline manufacturing process,environment,pipeline installation procedures,and inside medium.Then,this paper analyzes how the magnetic field on the craters affects the welding operation on the pipe.In such a case,a welding arc appears first at root welding,afterwards the magnetic blow occurs,having bad effects on the stability of arc,which will thus result in welding defects.In the end,this paper puts forward five methods for the pipe demagnetization based on the basic demagnetizing theories and practical experiences,including winding,adopting specialized facilities for demagnetization,heating-up,bridging,and cleansing.