The following terms are used to describe the parts or sections of a weld:

Fusion Zone (Filler Penetration). The fusion zone is the area of base metal melted as determined in the cross section of a weld.

Leg of a Fillet Weld. The leg of a fillet weld is the distance from the root of the joint to the toe of the fillet weld. There are two legs in a fillet weld.

Root of the Weld. This is the point at which the bottom of the weld intersects the base metal surface, as shown in the cross section of weld.

Size of the Weld.

  • Equal leg-length fillet welds. The size of the weld is designated by leg-length of the largest isosceles right triangle that can be scribed within the fillet weld cross section.
  • Unequal leg-length fillet welds. The size of the weld is designated by the leg-length of the largest right triangle that can be inscribed within the fillet weld cross section.
  • Groove weld. The size of the weld is the depth of chamfering plus the root penetration when specified.

Throat of a Fillet Weld.

  • Theoretical throat. This is the perpendicular distance of the weld and the hypotenuse of the largest right triangle that can be inscribed within the fillet weld cross section.
  • Actual throat. This is distance from the root of a fillet weld to the center of its face.
  • Face of the Weld. This is exposed surface of the weld, made by an arc or gas welding process on the side from which the welding was done.

    Toe of the Weld. This is the junction between the face of the weld and the base metal.

    Reinforcement of the Weld. This is the weld metal on the face of a groove weld in excess of the metal necessary for the specified weld size.

    Sections of a Weld