In the submerged arc welding zone, defects such as blowhole, hot crack and undercut are easy to occur.
1, foam. The main reason is the bubble occurred in the weld hydrogen remains hidden in the formation of air bubbles in the weld metal, so the elimination of defects is the first measurement of welding wire and welding seam must remove rust, oil, water and other substances, then you need to do to remove the moisture flux. In addition, increasing the current, reducing the welding speed, and slowing down the melting speed of molten metal are also very effective.
2, sulfur cracks (sulfur caused by cracks). Steel segregation region (especially mild steel) crack segregation of sulphur. The reason is the presence of hydrogen in the sulfur segregation zone containing low melting point iron sulfides and steels. Therefore, in order to prevent this, sulfur segregation using less semi killed steel or killed steel is also effective. Second, the cleaning and drying of weld surfaces and fluxes are also essential.
3, hot crack. In submerged arc welding, hot cracks occur in the weld, especially in the arc and arc. In order to eliminate this crack, the spiral welded pipe can be welded in reverse direction, usually at the end of the arc and arc installation plate and the end of the coil end welding. Thermal cracking is most likely to occur when the welding stress is greater or when the weld metal is very high.
4, the accumulation of slag. The welding residue involves the residual metal of the partial slag.
5, poor penetration. There is not enough overlap between the inside and outside of the weld, and sometimes it can not penetrate. This condition is known as lack of penetration.
6, the undercut is the V groove of the weld edge along the centerline of the weld. When the welding speed, current, voltage and other conditions are not appropriate, it will produce undercut phenomenon. If the welding speed is higher than the current, it is unlikely to cause undercut defects.