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Causes and preventive measures of undercut of submerged arc welded steel pipe

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Causes and preventive measures of undercut of submerged arc welded steel pipe

What is the undercut of submerged arc welded steel pipe?

The undercut is a product defect produced during high-speed welding is spiral submerged arc welded pipes. This defect makes the weld seem particularly affected. And this defect mainly has several manifestations: single unilateral undercut, single bilateral undercut, unilateral continuous undercut, and bilateral continuous undercut

Causes and preventive measures of a single unilateral undercut:

1. Reasons for formation

The formation of a single unilateral undercut is sporadic without regularity, excessive changes in the forming seam, small burrs or gaps on the edge of the strip, and wrong edges in the forming may all form a single undercut. For single-sided undercuts that meet the scope of the standard permit, the undercuts can be eliminated by grinding, and for undercuts that exceed the standard scope, they can be eliminated by repairing.

2. Preventive measures

When conditions permit, the edges of the strip steel should be treated as smooth as possible and the forming stability should be maintained. For the smoothness of the strip edge, an edge milling machine can be used instead of the disc cutter to cut the edge. Regarding the problem of forming stability, it can be solved by improving the adjustment and adjustment.

Causes and preventive measures of single bilateral undercut

1. Reasons for formation

①Welding wire joint

Due to changes in the diameter and smoothness of the welding wire joint, the wire feeding speed will suddenly change when the wire joint passes through the wire feed wheel, which will cause instantaneous changes in the welding voltage and melting speed, and the sudden widening and melting of the welding pool. Insufficient metal supplementation can be interpreted as a single double-sided undercut at this solder joint.

②Welding specification

Under normal circumstances, the welding specifications will not change significantly during the continuous production process. Therefore, there will be no undercut during the normal production process. However, under the influence of the external power source, the welding current and voltage may also undergo sudden changes, and the result of the sudden changes will eventually lead to the generation of undercuts.

③Instant short circuit

Sometimes due to board edge burrs or metal burrs mixed in the flux, an instantaneous short circuit occurs at the contact tip during normal welding. The instantaneous short circuit will cause instantaneous changes in welding current and voltage, and eventually cause undercuts. The treatment of a single double undercut is the same as that of a single undercut, and it can be treated by grinding or repairing.

2. Preventive measures

①Handle the welding wire joint

For the welding wire manufacturer, the joint should be heat treated to keep the hardness of the entire wire consistent. In the continuous production process of submerged arc welded steel pipes, when welding wires are connected, the joints should be ground after the completion of the butting to achieve a smooth transition and uniform diameter, and use an oxyacetylene gun to bake the front and back welding wires at the joints and allow them to cool down naturally. , To achieve the purpose of consistent hardness.

②Strictly control welding specifications

Pay attention to the change of current and voltage during welding. If the change is too large, find out the cause of the power supply and the external power supply of the system, so that the change of the specification is controlled within the allowable range.