There are some defects in the production of spiral steel pipe. There are some defects such as air hole, hot crack and undercut in
submerged arc welding zone. Today, the spiral tube manufacturer will show you some of the reasons for the defects.
1。 Undercut. Undercut is a V-groove along the weld center line of the weld edge. When the welding speed, current, voltage and other conditions are not suitable, undercut will occur. Among them, too fast welding speed is more likely to cause undercut defects
than improper current.
2。 Bubbles. Bubbles often appear in the weld center of spiral steel pipe. The main reason is that they are still hidden in the weld metal in the form of bubbles. Therefore, the measures to eliminate such defects are to remove
rust, oil, moisture and other substances on the welding wire and weld, and then dry the flux to remove moisture. In addition, it can effectively increase the current, reduce the welding speed and slow down the solidification speed of liquid metal
3。 Sulfur cracking. When the steel plate with strong sulfur segregation zone is welded, the sulfide in the sulfur segregation zone enters the weld metal and produces cracks. This is due to the existence of low melting point iron sulfide and steel
in the sulfur segregation zone. Therefore, in order to prevent this, it is effective to use semi killed steel or killed steel with less sulfur segregation zone. Secondly, the weld surface and flux should be cleaned and dried.
4。 Hot cracks. In the
process of submerged arc welding, hot cracks will be produced in the weld bead, especially in the arc starting and arc extinguishing pits. In order to eliminate this kind of crack, the backing plate is usually installed at the arc starting point and the
arc extinguishing point. At the end of the coil butt welding, the spiral welded pipe can be back welded into stack welding. When the welding stress is large or the silicon content in the welding metal is high, the hot crack is most likely to occur.