What is the result of having dirt or grease on the surfaces to be welded?

When surfaces to be welded have dirt or grease, it can lead to oxidation problems. Contaminants such as grease, oil, or dirt can form an unwanted barrier that inhibits proper fusion of the metals being joined. This barrier prevents the welding process from establishing a clean bond between the surfaces, resulting in defects such as porosity, weak joints, or incomplete fusion.

Oxidation occurs because the presence of contaminants can react with the filler material or the base metal during the welding process, creating oxides that compromise the integrity of the weld. A weld that is compromised due to such contamination may appear acceptable visually but will not have the desired mechanical properties, leading to potential failures under load or stress. Therefore, ensuring that surfaces are clean and free of contaminants is essential for achieving strong, reliable welds.

In contrast, other options do not accurately reflect the consequences of having dirty or greasy surfaces. Stronger welds, increased heat retention, and better aesthetic appearance would not occur when contaminants are present, as they detract from the quality and reliability of the weldment.