How can you tell if a weld is underfilled?

A weld is considered underfilled when the weld bead sits lower than the surrounding base material. This condition indicates that insufficient filler material was added during the welding process, which can result in a weakened joint and compromised structural integrity. The underfill creates a depression or gap that can be visually observed, making it easier to identify when performing inspections.

A weld bead that appears higher than the surrounding surface, is smooth and shiny, or shows excessive spatter does not indicate underfilling. In fact, a high weld bead suggests that it may have excessive material, while a smooth and shiny bead can often indicate proper technique and adequate filling. Excessive spatter might reflect issues related to welding parameters or technique, but it doesn’t inherently speak to the fill level of the weld. Each of these characteristics can be important for assessing weld quality, but the key indicator of underfilling remains the bead being lower than its surrounding area.