Nitrogen entering the weld pool from the atmosphere can cause which issue?

• A. Increased hardness
• B. Subsurface porosity and reduced penetration
• C. Faster weld speed
• D. Better corrosion resistance

Answer: (B)

Shielding the weld from air is essential because atmospheric gases can contaminate the molten metal. If nitrogen from the atmosphere leaks into the weld pool, it tends to come out of solution as the metal cools and forms gas pockets beneath the surface, creating subsurface porosity. This gas presence also disrupts the melt pool’s stability and heat flow, often reducing how deeply the weld fuses into the joint. So nitrogen contamination shows up as subsurface porosity and reduced penetration, rather than improving hardness, speed, or corrosion resistance.