Difference between welding pass, weld bead and welding layer


What is Welding Layer

A sequence of weld metal consisting of one or more weld passes/beads in a welding joint is called Welding layer. The layer may consist of one or more weld beads laid side by side as shown in below figure. As you will notice, the weld joint is welded in a number of passes which are the individual weld beads placed during the welding. Weld bead or weld pass are same terms.

The layers can have either a single weld bead or multiple weld bead placed within same level in the welding joint.

The weld macrograph of a single V joint given below shows that a number of weld beads are placed in the groove to fill the joint, but if we draw number of layers, we can see that each layers consists several number of weld beads or passes.

The root is started with one weld pass and nos. of passes per layer is increasing as the groove width is increasing. We can see that the final weld bead has highest number of weld passes.

What is A Weld Bead or Pass

Weld bead or weld pass or weld run can be defined as the single progression of a welding or surfacing method along a welding joint, weld deposit or on a base material. The result of a welding pass is a weld bead or weld layer.

As you will notice in above picture, Left hand side, it contains multiple passes in each layer except first and 2nd pass (only 1 weld bead in pass 1 & 2) while the picture on right hand side shows that each layer only contains single weld bead/ weld pass only. So, a layer can have more than 1 passes but 1 pass is going to be a part of one layer only.

If we consider the principle of weld bead or weld, they can be defined as:

  1. Single pass or single run weld
  2. Multipass weld or multi run

In a single pass or single run, only one weld bead is placed while in a multipass or multi-run weld, multiple weld beads are placed as shown in the below figure for a fillet weld joint. In the left hand side image, the fillet weld is welded using a single weld run, hence it’s a single pass weld. While on the right hand side image, the fillet weld is welded using 3 weld passes so it is a multipass weld.

Below example is given for single pass/ single run and multipass/multirun weld in a groove or butt weld joint.

What is Capping Layer in Welding

Capping layer is a nonstandard term for the final layer of a groove/ butt weld joint. This is the weld pass/ passes which is visible on the surface of a final completed weld in a groove weld. The top weld pass in below picture form the capping pass or capping bead or also called cover pass in a welding. When we say capping layer, it will cover the number of passes in the final layer and can have either a single pass or multipass in same layer.

What is Cover pass or cap pass in Welding

Weld pass (single pass weld) or welding passes deposited in layer & those are exposed to the surface from the side where welding was done, is called cover pass or capping run. A weld bead resulting from a cover pass is called cover bead or capping bead. An example of cover pass in shown in above picture.

What is Surfacing?

Surfacing a welding technique used to weld deposit on the base metal surface (either similar metallurgy in case of material thickness loss, called weld built up or different metallurgy known as weld overlay or cladding for corrosion protection or hard facing etc. Surfacing applications such as weld overlay, cladding and hard facing all are example of Weld Surfacing.

What is Weld Buttering?

Weld Buttering: Weld buttering is the process of depositing weld metal on a base metal to achieve the dimensional tolerances. E.g., Due to wrong weld face preparation or sometimes excessive material cutting, the weld face is buttered using same metallurgy welding rod to restore the base material thickness.

Butting is also used for welding of dissimilar weld joints to avoid pwht. One case is, when welding Cr-Mo material to stainless steel, Cr-Mo material is buttered using SS309L filler wire followed by PWHT. This buttered part then welded to stainless steel to avoid PWHT of stainless steel material while for Cr-Mo where PWHT is mandatory is already carried out.

What is Weld Builtup?

Weld Builtup: Weld builtup is a type of surfacing method used to deposit similar metallurgy weld on components which has got material loss due to erosion or corrosion. The term is widely used in oil & gas to perform weld deposit in vessels, columns, pump casting etc.

Corrosion Resistance Overlay (CRO) and Hard-Facing Overlay (HFO)

Click here to Know what is Corrosion Resistance overlay (CRO), Weld Overlay and Hard-Facing Overlay (HFO)

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