Common defects in the welding area of spiral welded steel pipes

Common defects in the welding area of spiral welded steel pipes:

Defects that are prone to occur in the submerged arc welding zone include 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 in the weld metal in the form of bubbles. Therefore, the measure to eliminate this defect is to first remove the rust, oil, water and moisture from the welding wire and weld. and other substances, followed by the fact that the flux must be dried well 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.

Preventive measures: Generally speaking, weld pores and slag inclusion defects caused by contamination of the welding wire or flux are continuous. When the imaging system finds that the entire weld has pores or slag inclusions, the welding wire and flux should be considered first. Check the purity of the welding wire, replace the flux, and check whether there is oil stains or rust on the surface of the welding wire. Another situation is that the pre-welded weld itself has a honeycomb-shaped gas connection. To ensure that the internal welding is not in the coal kiln, the current of wire 1 and wire 2 needs to be increased, or the welding speed must be reduced to make the pores in the melt. There is plenty of time to emerge from the pool.

 
2. Sulfur cracking (cracks caused by sulfur). 
Cracks caused by sulfides in the sulfur segregation zone entering the weld metal when welding plates with strong sulfur segregation zones (especially soft boiling steel). The reason is that the sulfur segregation zone contains low melting point iron sulfide and the presence of hydrogen in the steel. Therefore, in order to prevent this situation, it is effective to use semi-killed steel or killed steel with less sulfur segregation zone. Secondly, it is also necessary to clean and dry the weld surface and flux.

3. Thermal cracks. 

In submerged arc welding, hot cracks can occur in the weld bead, especially in the arc starting and arc extinguishing craters. In order to eliminate this kind of crack, backing plates are usually installed at the arc starting and arc extinguishing points, and at the end of the plate coil butt welding, the spiral welded pipe can be reversed and welded into the stack welding. Hot cracks are most likely to occur when the weld stress is high or when the Si content in the weld metal is high.

Preventive measures: When a crack is found, pickling samples or repair welding gouging are required to confirm whether it is an internal welding crack or an external welding crack. Cracks that appear in precision welding are generally external welding cracks. The prevention method is to reduce the welding line energy, that is, reduce the welding current and arc voltage of the external welding wire, reduce the eccentricity of the external welding, and increase the dry elongation of the external welding wire.

 
4. Inclusion of welding slag. 
The inclusion of welding slag means that part of the welding slag remains in the weld metal.
 
5. Poor welding penetration. 
The metal overlap of the inner and outer welds is not enough, and sometimes the welding is not penetrated. This condition is called insufficient weld penetration.
 
6. Undercut. 
Undercut is a V-shaped groove appearing on the edge of the weld along the center line of the weld. Undercut occurs when welding speed, current, voltage and other conditions are inappropriate. Among them, too high welding speed is more likely to cause undercut defects than inappropriate current.

Go here to learn more: Matters needing attention when purchasing welded steel pipes