Common Defects in the Welding Zone of Industrial Spiral Submerged Arc Welded Steel Pipes

Defects prone to occur in the welding zone of spiral submerged arc welded steel pipes include porosity, hot cracking, and undercut.

1. Bubbles. Bubbles often occur in the center of the weld bead. The main reason is that hydrogen gas remains hidden inside the weld metal in the form of bubbles. Therefore, to eliminate this defect, firstly, remove rust, oil, moisture, and other substances from the welding wire and weld. Secondly, thoroughly dry the flux to remove moisture. In addition, increasing the current, reducing the welding speed, and slowing down the solidification rate of the molten metal are also very effective.

2. Sulfur Cracks (Cracks Caused by Sulfur). Cracks occur when welding plates with strong sulfur segregation bands (especially soft-boiling steel) and sulfides from the sulfur segregation bands enter the weld metal. This is because the sulfur segregation bands contain low-melting-point iron sulfides, and hydrogen gas is present in the steel. Therefore, to prevent this, using semi-killed or killed steel with fewer sulfur segregation bands is also effective. Furthermore, cleaning and drying the weld surface and flux are also essential.

3. Hot Cracks. Hot cracks can occur in the weld bead during submerged arc welding, especially at the arc initiation and extinguishing craters. To eliminate these cracks, backing plates are usually installed at the arc initiation and extinguishing points, and at the end of the plate-coil welding, the spiral welded pipe can be reversed to weld into the lap weld. Hot cracks are prone to occur when the weld stress is high or when the weld metal is very thick.

4. Slag Inclusion. Slag inclusion refers to the presence of residual slag in the weld metal.

5. Poor Penetration. Insufficient overlap between the inner and outer weld metals, sometimes resulting in incomplete penetration. This condition is called insufficient penetration.

6. Undercut. Undercut is a V-shaped groove appearing along the weld centerline at the weld edge. Undercut occurs when the welding speed, current, voltage, and other conditions are inappropriate. Excessive welding speed is more likely to cause undercut defects than unsuitable current.