What is porosity in GTAW and what are common causes?

• A. Gas pockets in weld metal due to welding too fast.
• B. Deliberate porosity for filler lubrication.
• C. Gas pockets within the weld metal; caused by moisture, oil/grease, surface oxides, or shielding gas flow issues.
• D. Porosity is not related to gas flow.

Answer: (C)

Porosity is gas pockets trapped in the weld metal as it cools and solidifies. In GTAW, these pores form when gas from contaminants or the shielding gas gets into the molten weld pool and cannot escape before solidification. The common causes are:

• Moisture or humidity on the metal or in cleaning solvents. When heated, this moisture releases hydrogen, which forms bubbles in the weld.

• Oil, grease, or other hydrocarbon contamination. Hydrocarbons decompose in the heat and release hydrogen, creating porosity.

• Surface oxides on the base metal. Oxide films can decompose and generate gases or trap gas in the weld pool, leading to pores.

• Shielding gas flow problems. If shielding gas protection is inadequate—due to low flow, leaks, or drafts—the weld pool is exposed to air, allowing air-derived gases (and contaminants) to enter and form porosity.

Porosity weakens the weld by introducing voids and reducing metal density. Proper cleaning, drying, and ensuring solid shielding gas coverage are key to preventing it.

The other ideas don’t fit because porosity isn’t caused by simply welding too fast, isn’t something deliberate to lubricate filler metal, and is directly related to gas management and contamination, including shielding gas flow.