Weld penetration is defined as:

Weld penetration is defined as:

• A. The depth the weld fuses into the base metal
• B. The width of the weld bead
• C. The heat-affected zone diameter
• D. The weld's electrical resistance

Answer: (A)

Penetration describes how deep the base metal actually melts and fuses with the weld metal. It tells you how far the weld has fused into the joint thickness. When penetration is full, the weld fuses through the entire thickness of the base metal, creating a stronger joint; partial penetration means only part of the thickness is fused, which can weaken the joint. The other ideas aren’t about how deep the weld fuses: the width of the weld bead is a surface dimension, the heat-affected zone is the area heated enough to change the metal’s properties without melting, and the weld’s electrical resistance isn’t a measure of how deeply the metal fused. Understanding penetration helps ensure there’s enough fusion to carry the intended loads.

Penetration describes how deep the base metal actually melts and fuses with the weld metal. It tells you how far the weld has fused into the joint thickness. When penetration is full, the weld fuses through the entire thickness of the base metal, creating a stronger joint; partial penetration means only part of the thickness is fused, which can weaken the joint. The other ideas aren’t about how deep the weld fuses: the width of the weld bead is a surface dimension, the heat-affected zone is the area heated enough to change the metal’s properties without melting, and the weld’s electrical resistance isn’t a measure of how deeply the metal fused. Understanding penetration helps ensure there’s enough fusion to carry the intended loads.