In flux-core welding, what is the most likely cause of porosity?

• A. Contamination
• B. Moisture
• C. Low welding current
• D. Incorrect shielding gas

Answer: (B)

Porosity shows up as gas pockets trapped in the solidifying weld. In flux-core welding, hydrogen porosity is a common type. The flux inside the core is hygroscopic and can absorb moisture from the environment. When the arc heats the flux, that moisture releases hydrogen gas. The hydrogen then forms bubbles in the molten weld pool and, as the metal cools, those bubbles become porosity. So moisture in the flux (or flux storage) is the most likely source of porosity.

To prevent it, keep flux dry and properly stored, avoid welding in damp conditions, and use dry flux or re-dry flux per the manufacturer's guidelines. Other factors like surface contamination, insufficient current, or shielding gas issues can cause porosity in some situations, but moisture is the most common cause in flux-core welding.