Common Defects in Welding Area of Spiral Submerged Arc Welded Steel Pipe
Defects that are easy to produce in the submerged arc welding area 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. The second thing is to dry the flux well to remove moisture. In addition, it is also very effective to increase the current, reducing 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 and causes cracks. The reason is that the sulfur segregation zone contains low-melting iron sulfide and the presence of hydrogen in steel. Therefore, to prevent this, it is effective to use semi-killed steel or killed steel with less sulfur-containing segregation zone. Secondly, it is necessary to clean and dry the surface of the weld and the flux.
3. Thermal cracking. In submerged arc welding, thermal cracks can occur in the weld bead, especially at the arc starting and extinguishing arc craters. To eliminate this kind of 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 prone to occur when the weld stress is very high, or when the weld metal is very high.
4. The involvement of welding slag. The involvement of welding slag is a part of the welding slag remaining in the weld metal.
5. Poor weld 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. The undercut is along the centerline of the weld