CSA Welded Steel Construction – Metal Arc Welding (W59) Welding Inspector Level 1 Practice Test

Penetration depth describes how far weld metal fuses into the joint thickness. A fillet weld sits at the corner of the two pieces and does not weld through the thickness like a groove weld designed for complete joint penetration. When the fillet angle is less than 60 degrees, the geometry of the weld reduces the effective fusion depth relative to the joint, so the weld does not achieve full-through fusion. That situation is classified as partial joint penetration. Complete joint penetration would require a groove weld intended to fuse through the full thickness, which a fillet weld does not provide. No penetration would imply no fusion at all, which isn’t the case here, and mixed penetration isn’t the standard classification for this scenario.