Causes and preventive measures of single and double undercuts in submerged arc welded steel pipes

1. Causes of formation
①Welding wire joint: Due to changes in the diameter and smoothness of the welding wire joint, the wire feeding speed of the welding wire joint will suddenly change when passing through the wire feed wheel, which will cause instantaneous changes in the welding voltage and melting speed and a sudden change in the welding molten pool. The widening and insufficient replenishment of molten metal can result in a single double-sided undercut at this solder joint.
②Welding specifications: Under normal circumstances, the welding specifications will not change significantly during the continuous production process. Therefore, there will be no undercuts during the normal production process. However, under the influence of an external power supply, the welding current and voltage may also undergo sudden changes, and the sudden changes will eventually lead to the generation of undercuts.
③Instant short circuit: Sometimes due to burrs on the edge of the board or metal burrs mixed in the flux, an instant short circuit will occur at the contact tip during normal welding. The instant short circuit will cause instantaneous changes in the welding current and voltage, eventually leading to undercuts. The treatment of a single double undercut is the same as the treatment of a single undercut and can be processed by grinding or repairing.

2. Preventive measures
① Handle the welding wire joints: For welding wire manufacturers, the joints should be heat treated so that their hardness is consistent with that of the entire welding wire. When butt-welding wires in the continuous production process of submerged arc welded steel pipes, the joints should be ground after the butt-joining is completed to achieve a smooth transition and uniform true diameter, and an oxyacetylene gun should be used to bake the front and rear welding wires at the joints and allow them to cool naturally. , to achieve the purpose of consistent hardness.
② Strictly control the welding specifications: Pay attention to the changes in current and voltage during the welding process. If the changes are too large, find the cause of the power supply and the power supply outside the system to control the changes in specifications within the allowable range.