What is the consequence of lost shielding gas coverage?

• A. The tungsten oxidizes and the weld becomes porous
• B. The arc becomes unstable but weld quality remains perfect
• C. The filler rod cannot be fed into the weld
• D. The weld metals become weldable without filler

Answer: (A)

Shielding gas provides an inert atmosphere around the tungsten and molten metal to keep air from reacting with the weld. When that coverage is lost, air can reach the hot tungsten and melt pool, causing oxidation of the tungsten and contamination of the weld. This contamination often shows up as porosity in the finished weld, since gases from the air get trapped as the weld cools. In short, loss of shielding gas leads to oxidation of the tungsten and a porous, weakened weld, rather than a clean, perfect joint.