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

During the production of spiral submerged arc welded (SSAW) steel pipes, various welding zone defects may occur if process parameters, material conditions, or welding environments are not properly controlled. These defects can affect weld quality, structural integrity, and long-term performance. Below are the most common weld defects observed in SSAW pipes and their typical causes.

1. Porosity (Weld Bubbles)

Porosity often appears near the center of the weld bead. The primary cause is the entrapment of hydrogen within the molten metal, which forms gas pockets during solidification.

Prevention Measures:

Thoroughly remove rust, oil, moisture, and contaminants from the welding wire and joint area.

Fully dry the flux to eliminate moisture content.

Increase welding current, reduce travel speed, and slow the cooling rate of the weld metal to allow gases to escape.

2. Sulfur-Induced Cracking

Sulfur cracks occur when plates with strong sulfur segregation—especially rimmed steels—release low-melting iron sulfides into the weld metal, combined with hydrogen present in the steel.

Prevention Measures:

Use semi-killed or fully killed steel with fewer sulfur segregation bands.

Ensure proper cleaning and drying of the weld surface and flux to minimize contamination.

3. Hot Cracking

Hot cracks may form in the weld bead during submerged arc welding, particularly at the arc ignition and crater areas. High welding stress or excessive weld thickness increases this risk.

Prevention Measures:

Use backing plates at arc start and stop positions.

At the end of strip-to-coil welding, reverse the pipe to complete a lap weld for better stress distribution.

Optimize welding parameters to reduce thermal stress concentration.

4. Slag Inclusion

Slag inclusion refers to pieces of non-metallic slag trapped within the weld metal due to improper flux melting or insufficient slag removal.

Prevention Measures:

Maintain correct welding angles and heat input.

Ensure proper slag removal between passes.

5. Incomplete Penetration

Incomplete penetration occurs when the inner and outer weld beads fail to overlap sufficiently, resulting in incomplete weld fusion.

Prevention Measures:

Adjust welding current and voltage to improve penetration.

Ensure proper alignment and accurate control of weld bead formation.

6. Undercut

Undercut appears as a V-shaped groove along the weld toe. It is typically caused by improper welding parameters, especially excessive travel speed.

Prevention Measures:

Reduce welding speed to avoid excessive metal wash-out.

Ensure welding current and voltage are within optimal operating ranges.