What are the common surface defects of the weld seams of stainless steel welded pipes

Common surface defects of stainless steel weld seams include those mentioned above such as pores, cracks, undercut, and weld spatter. There are also the following types:

Unfused zone

This refers to the parts where the weld metal and the base metal or the weld layers do not fully fuse. Its appearance characteristics usually manifest as a distinct boundary line between the weld and the base metal, or visible unfused gaps between the weld layers. The main causes include insufficient welding current, excessive welding speed, too small bevel angle, and the presence of oil stains or rust on the surface of the weldment that hinders fusion.

Burn-through

During welding, the depth of penetration exceeds the thickness of the workpiece, and the molten metal flows out from the back of the weld seam, resulting in a perforation defect. The burn-through area will show obvious holes, and in severe cases, it may even cause the weld seam to completely break. This is mainly caused by excessive welding current, too slow welding speed, excessive assembly gap of the weldment, or too small fillet.

Surface oxidation

The weld seam surface shows obvious color changes, such as blackening or yellowing. This is due to the high temperature during welding causing the stainless steel surface to react with oxygen, forming an oxide film. Insufficient protection gas flow, excessive ventilation in the welding environment, and poor quality of the welding material can all lead to surface oxidation. Surface oxidation not only affects the appearance of the weld seam but also reduces the corrosion resistance of the weld seam.

Spatter

During welding, molten metal particles fly out from the weld seam and adhere to the surface of the weldment around the weld seam. The spatter usually appears as metal particles of various sizes, making the weld seam surface unclean, increasing the workload for cleaning, and possibly affecting the appearance quality and corrosion resistance of the weldment. This is mainly caused by improper selection of welding parameters, such as unstable current and voltage, poor gas protection effect, or poor quality of the welding rod or wire.

Poor weld formation

The appearance shape of the weld seam does not meet the requirements, such as inconsistent width, uneven height, and irregular waves. This may be caused by unstable welding operation techniques, uneven welding speed, or fluctuations in welding current. Poor weld formation will affect the appearance of the weld seam and may also cause uneven stress on the weld seam, reducing its strength.