4.1 Welding Terminologies

Welding is very important in the industry. It's process is often taken for granted, as not many people know them well, especially for those who need to work with pipes but not on the fabrication floor. By extensively understanding these concepts, it improves communication between the various teams which in turn improves weld quality. Welding is the most commonly used joint in all process piping connections around the world. It can join similar materials, ferrous or non ferrous(brazing) or even dissimilar materials.

In this post, welding terminologies would be run through to familiarize with welding before proceeding further and more in dept into welding processes, discontinuities and other information.

Why weld pipes?
- Superior strength compared to other
- Proven and documented methods of joining which controls welder quality, process control and material quality.
- Welding is required to move forward to using other joints such as union joint and flange joint.

Different ways of specifying welds by different trades (Design Engineer vs Welding engineer)
Types of pipe weld normally specified by Design Engineers on Weld Map drawings
Butt weld - direct butt to butt join
Socket weld - fillet weld to a pipe connected to a recessed fitting
Field Weld - pre tack welded, allowance for field modification usually based on tolerance usually of about -+100mm
Tack Weld - pre weld, to join pipes before fully welded on the field.

Types of pipe weld normally specified by Welding Engineers on Welding Procedure Specification (WPS)
Bevel-groove weld
V-groove weld
J-groove weld
U-groove weld
Square groove weld
Fillet weld



Welding terminologies

Discontinuities
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.

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

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.

Flux
- 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

Slag
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.

Source: Weldguru.com

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.

SMAW
Shielded Metal Arc Welding or Stick welding, a type of manual welding which uses electrical arc current to melt the filler stick(electrode) and base metal.

Here's a clear visual explanation from ChuckE2009 of how it is done.

Source: ChuckE2009


GMAW
Gas Metal Arc Welding/Metal Inert Gas welding is a type of automatic fed welding process which uses a flexible wire electrode. During welding, electrode is fed from the feeder along with shielding gas.

Here's a clear visual explanation from Weldingtipsandtricks of how it is done.

Source: Weldingtipsandtricks


FCAW
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.

SAW
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.

Source: Redrockautomation

GTAW/TIG
Gas Tungsten Arc Welding or Tungsten Inert Gas welding is a type of automatic fed welding process which uses a tungsten non-consumable electrode on the cup. A separate filler rod (without flux) is manually fed to the joint together while the tungsten electrode is fired.

Here's a clear visual explanation from Weldingtipsandtricks of how it is done.

Source: Weldingtipsandtricks



X-RAY TEST
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.

PQR
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)

WPS
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.