What is a common cause of porosity in welds?

Porosity in welds refers to the formation of small gas pockets or voids within the weld metal, which can compromise the structural integrity of the weld. The primary cause of porosity is contamination from moisture, oil, or other foreign materials. When these contaminants are present on the surface of the base metal or filler material, they can vaporize during the welding process. This vapor can become trapped in the molten weld pool, leading to voids as the weld cools and solidifies.

Moisture, for instance, can come from the ambient air or from the surface being welded if it is not properly cleaned. Oil or grease left on the material can also cause similar issues. Thus, ensuring that the materials being welded are clean and free from contaminants is crucial for preventing porosity.

Other factors, such as excessive heat application, improper joint design, or inadequate welding speed, may affect the overall quality of the weld but do not directly cause porosity in the same way that contamination does.