1, according to the use, welded steel pipes have general use and high temperature and high pressure use. The pipe used in the latter is often special alloy steel, so it is necessary to consider and solve the shrinkage crack problem in the welding process and the mechanical properties of the pipe in the heat affected zone will not change greatly due to the influence of welding operation.
2. According to the thickness of the pipe wall, pipes made of relatively thin materials such as steel belts can be welded by high frequency, and some thin-walled pipes can be welded by shielding gas; Pipes with wall thickness exceeding 2mm can be welded by manual arc welding.
3, according to the diameter of the pipe, small diameter can only be welded on one side, and technicians can drill into the pipe for double-sided welding. One-sided welding requires welder technology and can realize double-sided welding. Through the steel ball test, it is ensured that the cross-sectional area passing capacity and weld formation meet the design requirements.
4. As long as the pipe is high-strength alloy steel, including alloy steel pipes with high temperature resistance, pressure resistance, wear resistance and low temperature resistance, the welding process should focus on preventing martensite structure and the tendency of cracks caused by welding at high temperature. The general requirement in the process is to select covered electrode.
And sent to the welder for use after baking as required. Before welding, both sides of the weld should be degreased, dehydrated, derusted and cleaned. The welding line energy should be as small as possible, and the swing during welding should be as small as possible. The layout of the last weld should produce annealing effect on the heat affected zone as much as possible. Slow cooling after welding, covering with asbestos cloth, etc.
5, in order to ensure the welding quality of the pipeline, welders should be trained and tested, and qualified.
In order to weld steel pipes well, welders should consider operation skills besides basic theory. The welding process of pipeline may include several postures, such as prone welding, vertical welding and overhead welding. When the pipe can't rotate, the selection of current should consider the formation of vertical welding and overhead welding. Some pipes are not very big, and the current cannot be adjusted in the middle. In this process, the stability and formation of the arc can be properly controlled, and the formation should be combined with the necessary oscillation.