One of the phenomena that are prone to occur in the welding area of spiral welded steel pipes are pores, hot cracks, and undercuts:
Bubbles. Bubbles mostly occur in 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 change this phenomenon is to remove rust, oil, water and moisture from the welding wire and weld. Remove, followed by drying the flux well to remove moisture. In addition, increasing the current, reducing the connection speed, and slowing down the solidification speed of the molten metal are also very effective solutions.
Crack (caused by cracks). When welding a plate with a strong segregation zone (soft boiling steel), the compounds in the segregation zone enter the weld metal and cause cracks. The reason is that the segregation zone contains low melting point iron and hydrogen in the steel. Therefore, in order to prevent this situation, it is effective to use semi-carbon steel or carbon steel with less segregation zones. Secondly, it is also necessary to clean and dry the weld surface and flux.
Thermal cracks. In submerged arc welding, hot cracks can occur in the weld bead, and cracks are prone to occur at the arc starting and arc craters. For this kind of crack, backing plates are usually installed at the arc starting and extinguishing points, and at the end of the plate-to-coil connection, the spiral welded pipe can be reversed and welded into the lap weld. Hot cracks are prone to occur when the weld stress is very high, or when the si in the weld metal is very high.
Inclusion of welding slag. The inclusion of welding slag means that part of the welding slag remains in the weld metal.
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 a connection speed is more likely to cause undercutting than an inappropriate current.
