Common defects in the welding zone of spiral submerged arc welded steel pipes

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

1. Bubbles. Bubbles mostly occur in the center of the weld bead. The main reason is that hydrogen is still hidden in the welded metal in the form of bubbles. Therefore, the measure to eliminate this defect is to first remove rust, oil, water, and moisture from the welding wire and weld. substance, followed by drying 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 cracking (cracks caused by sulfur). Cracks caused by sulfides in the sulfur segregation zone enter the weld metal when welding plates with strong sulfur segregation zones (especially soft boiling steel). The reason is that the sulfur segregation zone contains low melting point iron sulfide and the presence of hydrogen in the steel. Therefore, to prevent this situation, it is effective to use semi-killed steel or killed steel with less sulfur segregation zone. Secondly, it is also necessary to clean and dry the weld surface and flux.

3. Thermal cracks. In submerged arc welding, hot cracks can occur in the weld bead, especially in the arc starting and arc extinguishing craters. To eliminate this kind of crack, backing plates are usually installed at the arc starting and arc extinguishing points, and at the end of the plate coil butt welding, the spiral welded pipe can be reversed and welded into the stick welding. Hot cracks are prone to occur when the stress in the weld is very high, or when the pressure in the weld metal is very high.

4. Inclusion of welding slag. The inclusion of welding slag means that part of the welding slag remains in the weld metal.

5. Poor welding penetration. The metal overlap of the inner and outer welds is not enough, and sometimes the welding is not penetrated. This condition is called insufficient weld penetration.

6. Undercut. Undercut is a V-shaped groove appearing on the edge of the weld along the center line of the weld. Undercut occurs when welding speed, current, voltage, and other conditions are inappropriate. Among them, too high welding speed is more likely to cause undercut defects than inappropriate current.