What is the effect of moisture on MIG weld quality?

• A. Hydrogen in shielding gas can cause porosity.
• B. It improves strength.
• C. It reduces spatter.
• D. It promotes faster welding.

Answer: (A)

Moisture in MIG welding mainly causes hydrogen porosity. When water vapor is present in the shielding gas or on the filler wire, it breaks down in the arc and releases hydrogen. Hydrogen is very small and easily dissolves into the molten metal; as the weld solidifies and cools, the hydrogen comes out as gas pockets, creating porosity inside the weld. This porosity weakens the weld and can lead to cracking in some steels, especially if hydrogen levels are high.

So moisture doesn’t improve strength, reduce spatter, or speed up welding. It disrupts the weld quality by introducing hydrogen porosity, which is why keeping shielding gas and consumables dry is essential.