Prevention and Causes of Undercutting of Submerged Arc Welded Steel Pipe

Causes and preventive measures of single-sided undercut:

In the production process of submerged arc welded steel pipes, especially in high-speed welding, the undercut has become the main defect in the production process of spiral submerged arc welded steel pipes. The defect of undercut mainly has the following surface forms: single-sided undercut, single double-sided undercut, single-sided continuous undercut, and double-sided continuous undercut. The hazards of welds are great, and they become fatal defects of welds just as weld cracks and incomplete penetration. Therefore, we should attach great importance to taking measures for the generation of such defects.

1. Reasons for formation: Generally speaking, the formation of a single side undercut is sporadic and irregular. Excessive changes in the forming seam, small burrs or small gaps on the edge of the strip, and forming wrong sides may form a single undercut. For a single side undercut that meets the standard allowable range, the undercut can be eliminated by grinding, and for the undercut that exceeds the standard range, it can be eliminated by repairing.

2. Preventive measures: Due to the uncertainty caused by such defects, we do not need to make major adjustments. We can smooth the edge of the strip as much as possible and keep the forming stable as conditions permit. For the smoothness of the edge of the strip, the edge milling machine can be used instead of the disc shearing edge to solve the problem of forming stability, which can be solved by improving the shape adjustment.

Causes and preventive measures of single double-sided undercut

1. Causes

①Welding wire joint: Due to the change in the diameter and smoothness of the welding wire joint, the wire feeding speed will change suddenly when the welding wire joint passes through the wire feeding wheel, which will cause the instantaneous change of welding voltage and melting speed, and the sudden change of welding pool The widening and insufficient replenishment of molten metal can result in a single double-sided undercut at this weld.

②Welding specification: Under normal circumstances, the welding specification will not change greatly during the continuous production process, so there will be no undercut in the normal production process. However, under the influence of the external power supply, the welding current and voltage may also undergo sudden changes, and the result of the sudden change will eventually lead to undercutting.

③Momentary short circuit: Sometimes due to the burrs on the edge of the board or the metal burrs mixed in the flux, an instantaneous short circuit will occur at the contact tip during the normal welding process. The instantaneous short circuit will cause instantaneous changes in welding current and voltage, and eventually lead to undercutting. The treatment of a single double undercut is the same as that of a single undercut and can be processed by grinding or repairing.

2. Preventive measures

①Properly handle the welding wire joints: For welding wire manufacturers, heat treatment should be performed on the joints so that the hardness of the entire welding wire remains the same. When welding wires are butt welded in the continuous production process of submerged arc welded steel pipes, the joints should be ground after the butt joints are completed to achieve a smooth transition and uniform true diameter, and the front and rear welding wires at the joints should be roasted with an oxyacetylene gun and allowed to cool naturally, to achieve the purpose of consistent hardness.

②Strictly control the welding specifications: pay attention to the changes in current and voltage during the welding process. If the changes are too large, find out the cause of the power supply and the power supply outside the system, so that the changes in the specifications are controlled within the allowable range.