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, 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. Causes

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 don't have to make major adjustments, and 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 connector

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 widening and melting of welding pool Insufficient metal replenishment can result in a single double-sided undercut at this solder joint.

② Welding 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 burr on the edge of the board or the metal burr mixed in the flux, an instantaneous short circuit will occur at the contact tip during the normal welding process, which will cause an instantaneous change in the 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

① Handle the welding wire joint well

For welding wire manufacturers, heat treatment should be carried out at the joint to make its hardness consistent with the hardness of the entire welding wire. 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.

② Strict control of 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.