The submerged arc welding zone is prone to defects such as porosity, hot cracks, and undercutting.
Porosity: Porosity mostly occurs in the center of the weld bead. The primary reason is that hydrogen remains hidden within the weld metal in the form of bubbles. Therefore, measures to eliminate this defect include first removing rust, oil, moisture, and dampness from the welding wire and weld seam. Secondly, it is essential to thoroughly dry the flux to remove moisture. Additionally, increasing the current, reducing welding speed, and slowing down the solidification rate of molten metal are also effective methods.
Sulfur Cracking (Cracks Caused by Sulfur): When welding plates with strong sulfur segregation zones (especially soft rimmed steel), sulfides in these zones can enter the weld metal, leading to cracks. The reasons are the presence of low-melting-point iron sulfides in the sulfur segregation zones and hydrogen in the steel. To prevent this, using semi-killed steel or killed steel with fewer sulfur segregation zones is effective. Furthermore, ensuring the cleanliness and dryness of the weld surface and flux is also necessary.
Hot Cracks: In submerged arc welding, hot cracks can occur within the weld bead, particularly at the arc starting and stopping craters. To eliminate these cracks, backing plates are typically installed at the arc starting and stopping points. When welding spiral pipes, reversing the pipe and overlapping the weld at the end of the coil welding sequence can also help. Hot cracks are most likely to occur when the weld stress is high or when the silicon (Si) content in the weld metal is high.
Inclusion of Slag: Inclusion of slag refers to the residual presence of slag within the weld metal.
Inadequate Penetration: This occurs when the overlap of the internal and external weld metal is insufficient, sometimes resulting in incomplete penetration. This condition is known as inadequate penetration.
Undercutting: Undercutting is the formation of a V-shaped groove along the centerline of the weld at its edge. It arises due to inappropriate welding speed, current, and voltage settings. Among these factors, excessively high welding speed is more likely to cause undercutting than unsuitable current settings. The occurrence of undercutting in spiral pipes is higher than in general submerged arc straight seam welded pipes due to their unique configuration.
