Pipeline welding method
1) The pipelines connected by arc welding shall be constructed according to the procedures of pipeline straightening, cutting and blanking, groove processing, assembly, welding and slag cleaning on the basis of lofting and marking.
2) Groove processing and cleaning:] Generally, oxygen-acetylene flame gas cutting is used to cut the groove of the pipeline. After the gas cutting is completed, clean the iron oxide at the nozzle with a file, and smooth the uneven parts that affect the welding quality with a grinder. Small-diameter pipe shall be cut with grinding wheel cutter and portable electric pipe cutter as far as possible, and then the pipe mouth groove shall be processed with grinder. V-shaped groove is adopted for the pipeline groove, and the groove is polished by machining or grinding machine to be smooth and flat. Remove the oil, rust and moisture within 20mm on both sides of the groove, and ensure the metallic luster is exposed, ensure that the groove surface can not have cracks, interlayers and other defects, and remove the dirt inside and outside the groove.
3) covered electrode and flux should be dried according to the instructions before use, and kept dry during use. Covered electrode coating has no shedding and obvious cracks.
4) Nozzle assembly before welding: Nozzle assembly adopts special assembly tools to ensure the straightness and alignment of the pipeline. The combination of pipeline butt welds must be flush with the inner wall, and the deviation of the inner wall shall not exceed the standard; Pipeline components shall be fixed by welders who weld the same pipeline. Covered electrode or welding wire used for fixed point shall be the same as covered electrode or welding wire used for formal welding. The spot welding length is 10- 15mm, and the height is 2-4mm, which should exceed 2/3 of the thickness of the pipe wall. There shall be no cracks, pores, slag inclusions and other defects on the weld surface of the pipeline; After the pipes and fittings are fixed, the welding area should not be affected by harsh environmental conditions (wind and rain).
5) Welding construction must be carried out in strict accordance with the provisions of the welding work instruction; Welding equipment must be tested for safety and usability before use, and unqualified equipment is strictly prohibited from entering the construction site; Do a good job in self-inspection and mutual inspection during welding, and do a good job in process control of welding quality.
6) Manual arc welding shall be adopted for pipeline welding. Before use, covered electrode should be put into covered electrode drying oven and baked at 100℃- 150℃ for 1-2 hours, and the surface of covered electrode should be free of oil. When welding, pay attention to the quality of arc initiation and arc closing, ensure that the arc pit at the arc closing place is filled to prevent the arc pit from cracking, and ensure that the indirect ends of the layers are staggered during multi-layer welding. Each weld should be welded as soon as possible. If it is forced to stop for help, anti-crack measures should be taken in time to confirm that there is no crack before welding can continue.
7) When pipes are connected, they shall not be forcibly butted, especially when the bolts connected with the equipment are loose, the position of the butted part shall be correct.
8) Butt welds or flange interfaces on pipelines must avoid overlapping with supports and hangers. Opening and welding of instrument source components on the pipeline should be carried out before pipeline installation.
9) The welding slag on the weld surface must be cleaned up, and the appearance quality should be checked to see if there are welding defects such as blowholes, cracks and inclusions. If there is any defect, it must be repaired in time and recorded.