What are the common defects of stainless steel welding pipes

Underfilled: The phenomenon where the root of the joint is not fully welded during fusion welding is called underfilled. This defect may occur in single-sided and double-sided welding of stainless steel pipes and affects this technical flaw. The main reasons for forming underfilled are too low welding current, too fast welding speed, inappropriate groove size, or the welding wire not aligning with the center of the weld seam.

Unfused: During fusion welding, the weld metal of the stainless steel pipe and the base metal or between weld seams do not fully fuse. Unfused can be classified as side wall unfusion, interlayer unfusion, and root unfusion. The molten metal is pushed towards the tail by the arc force, forming a groove. When the arc moves forward, liquid metal is added to the groove, and if the liquid metal layer at the groove wall has already solidified and the heat from the incoming liquid metal is insufficient to melt it again, an unfused defect is formed. In submerged arc welding, slag may flow into the non-melting area of the welding zone. To prevent unfusion defects during high-speed welding, measures such as increasing the weld width or using double arc welding should be taken.

Burn-through: During the welding of stainless steel pipes, the molten metal flows out from the back of the weld seam, forming a perforation phenomenon called burn-through. This defect may be caused by excessive welding current, too low welding speed, or too large groove gap.

Edge gouging: The phenomenon where the base metal along the weld toe of the stainless steel pipe is melted and forms a depression or groove is called edge gouging. Edge gouging can be continuous or intermittent. This defect may occur during high-speed welding of stainless steel pipes. If the butt joint welding is improper, this defect may also occur.

Weld bead: The metal that flows out of the melting process of the stainless steel pipe material and flows onto the un-melted base metal outside the weld quality is called weld bead. At the weld bead, there is local unfusion. The weld seam is caused by excessive filling of metal, which is related to small gap and groove size, low welding speed, low voltage, or long welding wire extension length.

Underfilled: During the welding of stainless steel pipes, due to insufficient filler metal, a continuous or intermittent groove is formed on the surface of the weld seam, called underfilled.

Inclusions and slag: Inclusions are non-metallic inclusions and oxides produced by metallurgical reactions remaining in the weld metal. Slag is the remaining slag in the weld. Stainless steel welding pipes with slag can be classified into point-like slag and strip-like slag. Slag weakens the effective cross-section of the weld seam, thereby reducing the mechanical properties of the weld seam. Slag can also cause stress concentration and easily cause the welded structure to be damaged during loading.

Causes: Inadequate interlayer slag cleaning during the welding process; too low welding current; too fast welding speed; improper operation during welding; inappropriate chemical composition matching between the welding material and the base metal; inappropriate groove design and processing, etc.

Preventive measures: Select welding rods with good slag removal performance; carefully remove interlayer slag; reasonably select welding process parameters; adjust the angle and welding method of the welding rod.

In addition to the above defects, stainless steel pipes during welding also have defects such as back shrinkage groove, poor surface shape, excessive height, irregular surface, surface pores, root pores, poor weld seam connection, arc abrasion, and spatter, which are mostly caused by improper welding processes. Therefore, formulating appropriate stainless steel pipe welding processes and operating carefully can fundamentally prevent the occurrence of weld seam formation defects. Moreover, when certain process conditions change during the welding of stainless steel pipes, taking timely countermeasures is very important.