Which weld condition suggests contaminated shielding gas?

• A. Welds turn gray or sooty
• B. Welds turn bright blue
• C. Welds have a uniform shine
• D. Welds are perfectly clean

Answer: (A)

Shielding gas must completely blanket the weld pool. When the gas is contaminated or leaking, impurities enter the arc and oxidize or burn, leaving visible changes on the weld surface. A gray or sooty appearance is a classic sign of this contamination, often due to hydrocarbons, oil, moisture in the gas, or a leak in the gas delivery. These contaminants prevent full protection of the weld, causing dull, dirty, or blackened deposits. In contrast, a weld that turns bright blue usually points to overheating or oxidation from excessive heat input, not necessarily gas contamination, while a uniform shine or a perfectly clean weld indicates good shielding and proper cleanliness. So the gray or sooty look best signals contaminated shielding gas.