Welding Terminologies | Welding Terms and Definition

Welding Terminologies | Welding Terms and Definition

Welded joints are very common in engineering for the manufacture of fabricated assemblies. Previously riveted and bolted joints were often used for these type of assemblies. For example, in the Sydney Harbour Bridge almost all the joining of the metal plates has been done with rivets and bolts. Since the time of construction of the bridge there have been technological advances in welding so that nowadays bridges are almost always constructed using welded joints. Similarly ocean going vessels, steam boilers and other pressure vessels once used to be riveted but nowadays are welded. Riveting is still used for aircraft construction. Can you think why this is so?

Nowadays, fabrication using welds is often used rather than casting or forging for production of machine components (particularly if only small quantities are required). You can therefore see that a mechanical engineer needs to have a good understanding of the fabrication using welded joints and how to perform stress analysis on these fabrications.

Read more : What are the major welding application

weld section
weld terminology

Welding Terminologies

A flaw on the weld not desired, may be acceptable or unacceptable by inspectors depending on welding code specifications. Discontinuities are allowed, as long as they meet code requirements. The types of discontinuities described in AWS codes will be described in another post.

A flaw on the weld unaccepted by welding code specifications. Defects shall be rejected.

Backing – It is the material placed on the root side of a weld for supporting of molten metal until it solidies and facilitates complete penetration.

Cap – It is the last bead of weld joint.

Crater – The depression on weld at the point where the arc strikes the base metal.

Deposition rate – The rate at which welds metal is deposited on the base metal. It is expressed in kg/h.

Penetration – The maximum depth at which molten metal penetrates on base metal and then combines them. It is measured from the top surface of the joint.

Paddle – The hole in the weld joint created by the heat of welding. It is used when the sheet metal needed to weld together.

Tack weld – A small temporary welding to hold workpiece together during the actual welding.

Weld Pass – The single movement of the electrode or torch that results weld bead.

Weld bevel – Angle cut at the edge of base metal to assist penetration of molten metal.

Base metal
The material which the welder is expected to join.

Filler metal

The material which the welder applies to the base metal.

Weld metal

– A new metal formed by melting of base + filler metal.
– The reason why PQR is required to verify strength. Different material batch produces different weld strength.

– Provides the following to the weld process: shielding gas, interpass cooling temperature control by slag, reinforcement alloy to weld metal
– Present in SMAW & FCAW.
– Can cause inclusion discontinuity 

By-product of burning flux, needs to be remove before adding additional weld passes.

Weld Passes
The number of times the weld stick needs to pass between the gap to be welded. One who has never welded a pipe would think that one weld would close the gap, but it all depends on pipe size and thickness. For thicker pipes, more passes would be required usually in this manner root pass –> hot pass –> fill pass –> cover pass. On smaller pipes, less passes would be required.

Bevel size & angle
Size of slope for bevel, V, J, U groove welds and its angle. The lesser the angle, the less filler material is consumed.

Steeper angles for Bevel/V, usually around 37deg (Usually on process pipes)
Less Steep angles for J/U, usually around 20deg. (Usually on long distribution pipelines to save time and cost)

Groove face
Face of the bevel.

Root face
Face of the root.

Root gap
The gap between the base metal. Root gap depends on thickness of weld metal.

Weld toe
The top side of weld where filler metal and base metal touches.

Weld root

The bottom side of weld where filler metal and base metal touches.

Weld reinforcement
The height of the weld protrusion on top side of weld. Excessive reinforcement is a discontinuity, as it weakens the joint at the weld toe, as sharp corner induced stress.

Weld Face
The face of the weld looking from top side of the weld.

Root reinforcement

The protrusion on bottom side of weld. Excessive reinforcement is a discontinuity, as it weakens the joint at the weld root, as sharp corner induced stress.

Weld interface

The surface on base metal where filler metal are deposited.

Heat Affected Zone

A section on the base metal parallel to the fusion zone. This section is slightly harder which increases likelihood of embrittement cracking, the reason why pre-heating and PWHT are required, to slow down the annealing(cool down) which reduces hardness.

Fusion Zone

The area where new metal is situated after welding.

Fusion Face/Fusion Line

Same as weld interface, but a name used for when welding has complete.

Hydrogen induced cracking
When moisture content are present during welding, they break down under high temperature of approximately 3000 – 3500degC at the arc, hydrogen is produced and entrapped in the weldment. This will induce porosity and subsequently cracking.

Filler rod/Electrode

Commonly known as welding stick, consumable and many more, it transmit electricity to heat up the tip of electrode which melts it along with the base metal.

Weld cup

Commonly for gas welding, purpose of the cup is to reduce welder handshake during weld and is a nozzle for shielding gas. Filler wire is fed from the cup for GMAW/FCAW, no filler wire for GTAW.

Flux Core Arc Welding is a type of automatic fed welding process which uses a flexible tubular electrode with flux within the tube core. It is similar to GMAW, except with a flux core and that that shielding gas may or may not be used.


Submerged Arc Welding is a type of automatic fed welding process, where flux in powder form is laid before filler rod passes through the joint.

X-ray tests may or may not be conducted after welding to verify weld size for integrity and soundness, it usually depends on design parameter Ew (Welding efficiency) specified by design engineer.

Procedure Qualification Record. This is a record of the welders ability to perform certain type of welding process and the type of materials joined. Various tests are performed on the test coupon to verify the integrity and soundness of the joint
– Bend test
– Tensile test
– Ductility
– Hardness (Rockwell)
– Toughness (Charpy V-notch)


Welding Procedure Specification describes how the welding process will be performed. This specification needs to be backed up and referenced from the PQR. Welding inspectors will refer to these two documents to verify the weld preparation, interpass preparation and post welding inspection activities.

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Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

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