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Welding Terminology

• Arc Welding – A welding process that produces a coalescence of metals by heating them with an electric arc.
• Arc Welding Electrode – A part of the welding system that conducts current and ends at the arc.
• Back Gouging – The removal of weld and base metal from the other side of a partially welded joint. The objective is to assure complete penetration upon subsequent welding from that side.
• Backing – A piece of material placed at the root of a weld joint for the purpose of supporting molten weld metal.
• Base Metal – The metal to be welded.
• Bevel – An angled edge preparation.
• Butt Joint – A joint between two members lying in the same plane.
• Complete Fusion – Fusion over the entire fusion faces and between all adjoining weld beads.
• Complete Joint Penetration – A groove weld condition in which weld metal extends through the joint thickness.
• Defect – A discontinuity or discontinuities that, by nature or accumulated effect (for example, total crack length or amount of porosity), renders a part or product unable to meet minimum applicable acceptance standards or specifications.
• Depth of Fusion – The distance that fusion extends into the base metal or previous bead from the surface melted during welding.
• Facing Surface – The surfaces of materials in contact with each other and joined or about to be joined together.
• Filler Material – The material to be added in making a welded, brazed, or soldered joint.
• Fillet Weld – A weld of approximately triangular cross section that joins two surfaces approximately at right angles to each other in a lap joint, T-joint, or corner joint.
• Flat Welding Position – A welding position where the weld axis is approximately horizontal and the weld face lies in an approximately horizontal plane.
• Flux – Material used to prevent, dissolve, or facilitate removal of oxides and other undesirable surface substances.
• Flux Cored Arc Welding (FCAW) – An arc welding process that produces coalescence of metals by means of a tubular electrode. Shielding gas may or may not be used.
• Fusion – The melting together of filler metal and base metal, or of base metal only, to produce a weld.
• Gas Metal Arc Welding (GMAW) – An arc welding process where the arc is between a continuous filler metal electrode and the weld pool. Shielding from an externally supplied gas source is required.
• Gas Tungsten Arc Welding (GTAW) – An arc welding process where the arc is between a tungsten electrode (non-consumable) and the weld pool. The process is used with an externally supplied shielding gas.
• Groove Weld – A weld made in a groove between two members.
• Heat-Affected Zone (HAZ) – That section of the base metal, generally adjacent to the weld zone, whose mechanical properties or microstructure have been altered by the heat of welding.
• Hot Crack – A crack formed at temperatures near the completion of weld solidification.
• Incomplete Fusion – A weld discontinuity where fusion did not occur between weld metal and the joint or adjoining weld beads.
• Incomplete Joint Penetration – A condition in a groove weld where weld metal does not extend through the joint thickness.
• Interpass Temperature – In a multi-pass weld, the temperature of the weld area between passes.
• Joint – The junction of the edges of members that are to be joined or have been joined.
• Lap Joint – A joint type in which the non-butting ends of one or more workpieces overlap approximately parallel to one another.
• Leg of Fillet Weld – The distance from the root of the joint to the toe of the fillet weld.
• Metal Cored Arc Welding – An arc welding process with a tubular electrode where the hollow electrode contains alloying materials.
• Metal Cored Electrode – A composite tubular electrode consisting of a metal sheath and a core of various powdered materials, producing no more than slag islands on the face of the weld bead. External shielding is required.
• Peening – The mechanical working of metals using impact blows.
• Plug Weld – A circular weld made through a hole in one member of a lap or T-joint.
• Porosity – A hole-like discontinuity formed by gas entrapment during solidification.
• Post Weld Heat Treatment (PWHT) – Any heat treatment subsequent to welding.
• Preheating – The application of heat to the base metal immediately before welding, brazing, soldering, thermal spraying, or cutting.
• Preheat Temperature – The temperature of the base metal immediately before welding is started.
• Procedure Qualification Record (PQR) – The demonstration that the use of prescribed joining processes, materials and techniques will result in a joint exhibiting specified soundness and mechanical properties.
• Reinforcement – Weld metal, at the face or root, in excess of the metal necessary to fill the joint.
• Root Opening – A separation at the joint root between the work pieces. Root Crack – A crack at the root of a weld.
• Self-Shielded Flux Cored Arc Welding (FCAW-S) – A flux-cored arc welding process variation in which shielding gas is obtained exclusively from the flux within the electrode.
• Shielded Metal Arc Welding (SMAW) – A process that welds by heat from an electric arc between a flux-covered metal electrode and the work. Shielding comes from the decomposition of the electrode covering.
• Shielding Gas – Protective gas used to prevent atmospheric contamination.
• Submerged Arc Welding (SAW) – A process that welds with the heat produced by an electric arc between a bare metal electrode and the work. A blanket of granular fusible flux shields the arc.
• Tack Weld – A temporary weld used to hold parts in place while more extensive, final welds are made.
• Tensile Strength – The maximum stress a material subjected to a stretching load can withstand without tearing.
• Weld Bead – The metal deposited in the joint by the process and filler wire used.
• Welding Leads – The work piece lead and electrode lead of an arc welding circuit.
• Weld Metal – The portion of a fusion weld that has been completely melted during welding.
• Weld Pass – A single progression of welding along a joint. The result of a pass is a weld bead or layer.
• Weld Pool – The localized volume of molten metal in a weld prior to its solidification as weld metal.
• Weld Puddle – A non-standard term for weld pool.
• Welding Sequence – The order in which weld beads are deposited in a weldment.

Reprinted from the Michigan Department of Transportation Field Manual for Structural Welding.