Common defects in the welding area of ​​spiral seam submerged arc welding steel pipe

Defects that are prone to occur in the submerged arc welding area include pores, thermal cracks, and undercuts.

1. Bubbles. Bubbles often occur in the center of the weld. The main reason is that hydrogen is still hidden in the welded metal in the form of bubbles. Therefore, the measures to eliminate this defect are to first remove rust, oil, water, and moisture from the welding wire and weld, and secondly, to dry the flux well to remove moisture. In addition, increasing the current, reducing the welding speed, and slowing down the solidification rate of the molten metal is also very effective.
2. Sulfur cracks (sulfur-induced cracks). When welding plates with strong sulfur segregation bands (especially soft boiling steel), sulfides in the sulfur segregation band enter the weld metal and cause cracks. The reason is that the sulfur segregation band contains low-melting iron sulfide and hydrogen exists in the steel. Therefore, to prevent this situation from occurring, it is effective to use semi-killed steel or killed steel with fewer sulfur segregation bands. Secondly, cleaning and drying the weld surface and flux are also very necessary.
3. Thermal cracks. In submerged arc welding, thermal cracks can occur in the weld, especially in the arc pits at the start and end of the arc. To eliminate such cracks, pads are usually installed at the start and end of the arc, and at the end of the plate coil welding, the spiral welded pipe can be reversed and welded into the overlap weld. Thermal cracks are easy to occur when the stress of the weld is very large or the weld metal is very high.
4. Slag inclusion. Slag inclusion means that a part of the slag remains in the weld metal.
5. Poor penetration. The overlap of the inner and outer weld metals is not enough, and sometimes it is not welded through. This situation is called insufficient penetration.
6. Undercut. Undercut is a V-shaped groove on the edge of the weld along the center line of the weld. Undercut is caused by inappropriate conditions such as welding speed, current, and voltage. Among them, too high a welding speed is more likely to cause undercut defects than inappropriate current.