Anatomy of a weld

Face, toes, root, throat, HAZ — the words you will write on the practical report.

Learn the parts so your practical reports sound like an inspector, not a welder swapping stories.

Part	Where it is	Why you care
Weld face	Exposed surface of the weld	Porosity, underfill, excess reinforcement, ripple
Weld toe	Junction of face and base metal	Undercut, toe cracks, overlap
Weld root	Opposite the face, deepest point	Lack of penetration, root concavity, suck-back
Weld metal	Fused filler + melted base	Slag, porosity, cracks in the bead
Fusion zone	Where weld metal meets unmelted base	Incomplete fusion lives here
HAZ	Base metal altered by heat, not melted	Hydrogen cracks, hardness, underbead cracking
Leg	Distance from root to toe on each member	Fillet size
Actual throat	Shortest path from root to face	Strength of a fillet
Effective throat	Design throat used for strength	PJP size; fillets often 0.707 × leg

Heat input (remember the formula)

HI (kJ/mm) = (V × A × 60) / (S × 1000)

V in volts, A in amperes, S travel speed in mm/min. Some papers use kJ/in with in/min. Same idea. High heat input grows grains and can drop toughness; low heat input on hardenable steel can crack.

Preheat: heating the joint before welding to slow cooling, drive off moisture, and cut hydrogen-crack risk.
Interpass temperature: the temperature of the weld area before the next pass. Too high can wreck toughness; too low reintroduces hydrogen risk.
Residual stress: locked-in stress from shrinkage. Distortion is residual stress that won.
Backing: material at the root that supports molten metal. May be fused (remaining) or removed.
Back gouging: removing metal from the second side to sound weld metal before welding the second side of a CJP.

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