At present, the long-distance pipeline construction in China generally adopts the “cellulose-type electrode down welding, cellulose-type electrode root welding + self-shielded flux-cored wire semi-automatic welding and STT root welding + self-shielded flux-cored wire semi-automatic welding” process, which is easy to weld. The problems that arise are:
1, slag inclusion
Reason: Because the long-distance transmission pipeline mostly adopts the semi-automatic down welding process of flux cored wire to fill and cover the surface, when the semi-automatic equipment has intermittent failure in the welding process, the top wire phenomenon often occurs. At this time, the welding wire penetrates the molten pool and melts. When the pool rapidly cools down and ignites again, metal inclusions or slags are often wrapped in the welds, resulting in slag inclusions.
Measure: Be careful to clean the groove before root welding. Carefully clean the slag when filling and capping.
Reason: The filling layer porosity is mainly due to the arc voltage being too high when the self-shielding flux core is semi-automatically welded.
Measures: During the welding process, select the appropriate arc voltage and wire feed speed, maintain a certain length of wire extension, and control the appropriate welding speed when down welding.
3, the roots are not thoroughly penetrated
Causes: The main reason is that the group is too small or the blunt edge is too thick.
Measure: Carefully grind and weld the weld before welding to ensure that the wire or electrode can extend smoothly into the root of the groove when the root is welded. When the root can not be dissolved, the root clearance of the application is ground and the welding parameters are properly adjusted. .
Cause: Forced pairs often cause cracks during welding.
Measures: 1) Avoid forced pairing; 2) Preheat before welding, increase the thickness of the root bead appropriately, and immediately heat-weld, fill, and cover after root welding.
5, burn through
Cause: Due to too thin root pass or improper welding process parameters.
Measures: The root pass should not be too thin, suitable for 3mm thick; root welding process parameters should not be too large; immediately after burning to stop welding, need to grind the groove angle and root gap, and then re-root welding, heat welding To complete the process.