Spiral welded pipe is a welded tube made by rolling low-carbon carbon structural steel or low-alloy structural steel strip into a tube blank at a certain helical angle (called forming angle), and then welding the pipe seams. It can produce large-diameter steel pipes from narrower strips
Defects that are easy to produce in the submerged arc welding zone are 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 inside the weld metal in the form of bubbles. Therefore, the measure to eliminate this defect is to first remove the rust, oil, moisture and moisture of the welding wire and weld. For other substances, the flux must be dried well to remove moisture. In addition, it is also very effective to increase the current, reduce the welding speed, and slow down the solidification speed of the molten metal.
2. Sulfur cracking (crack caused by sulfur). When welding plates with a strong sulfur segregation zone (especially soft boiling steel), the sulfide in the sulfur segregation zone enters the weld metal to produce cracks. The reason is that the sulfur segregation zone contains low-melting iron sulfide and the presence of hydrogen in steel. Therefore, in order to prevent this, it is effective to use semi-ballasted steel or ballasted steel with less sulfur-containing segregation zone. Secondly, the cleaning and drying of the weld surface and flux are also necessary.
6. Undercut. Undercut is the appearance of a V-shaped groove at the edge of the weld along the center line of the weld. The undercut is produced when welding speed, current, voltage and other conditions are not appropriate. The welding speed is too high to cause undercut defects more easily than the current is not suitable.
Defects that are easy to produce in the submerged arc welding zone are 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 inside the weld metal in the form of bubbles. Therefore, the measure to eliminate this defect is to first remove the rust, oil, moisture and moisture of the welding wire and weld. For other substances, the flux must be dried well to remove moisture. In addition, it is also very effective to increase the current, reduce the welding speed, and slow down the solidification speed of the molten metal.
2. Sulfur cracking (crack caused by sulfur). When welding plates with a strong sulfur segregation zone (especially soft boiling steel), the sulfide in the sulfur segregation zone enters the weld metal to produce cracks. The reason is that the sulfur segregation zone contains low-melting iron sulfide and the presence of hydrogen in steel. Therefore, in order to prevent this, it is effective to use semi-ballasted steel or ballasted steel with less sulfur-containing segregation zone. Secondly, the cleaning and drying of the weld surface and flux are also necessary.
3.Thermal cracking. In submerged arc welding, thermal cracks can occur in the weld bead, especially at the arc starting and extinguishing arc craters. In order to eliminate such cracks, backing plates are usually installed at the arc starting and arc extinguishing positions, and at the end of the coil butt welding, the spiral welded pipe can be reversed and welded into the overlap welding. Hot cracks are most likely to occur when the weld stress is high, or when the si in the weld metal is high.
4.The involvement of welding slag. Involvement of welding slag is a part of welding slag remaining in the weld metal.
5.Poor penetration. The overlap of the inner and outer weld metal is not enough, and sometimes the weld is not penetrated. This situation is called insufficient penetration.
6. Undercut. Undercut is the appearance of a V-shaped groove at the edge of the weld along the center line of the weld. The undercut is produced when welding speed, current, voltage and other conditions are not appropriate. The welding speed is too high to cause undercut defects more easily than the current is not suitable.
