Porosity

Porosity represents a critical weld defect because isolated gas pockets act as stress risers that initiate fatigue cracks under cyclic loading, even when the bulk of the weld is sound. Common causes include contaminated base metal surfaces contaminated with oil, scale, or paint; inadequate shielding gas coverage from improper nozzle positioning or wind conditions; and moisture in filler metal or flux that decomposes and generates hydrogen gas.

Prevention requires careful pre-weld cleaning, verification of shielding gas purity and flow rate, protection of the weld zone during welding, and attention to arc parameters that promote smooth, bubble-free pool action. Weld inspection techniques such as radiographic testing or ultrasonic examination reliably detect porosity, making it essential to include these methods in any weld certification or qualification program for safety-critical applications.