Welding Symbols

Welding symbols let a drawing specify the type, size, location and finish of a weld without needing a separate note for every joint. This page covers how a full welding symbol is built up, the basic weld type symbols, the supplementary symbols used to add extra instructions to a weld symbol, and the weld face (contour) symbols shown on the near and far side of a joint, referencing both the international ISO 2553 standard and the US AWS A2.4 standard.

The elementary weld symbols themselves are identical, or very close to identical, between the two standards — the real differences between ISO 2553 and AWS A2.4 mostly show up in how the full welding symbol is built up around them (arrow/reference line conventions, tail contents, and some supplementary symbols). Where that's the case it's noted in the table.

ANATOMY OF A WELDING SYMBOL

A basic weld symbol on its own only shows the weld type. A full welding symbol wraps that basic symbol in a small amount of extra notation that tells the welder which side of the joint to weld, how big to make it, how long to run it, and any process reference — all without extra notes cluttering the drawing.

1. Arrow line — points from the reference line to the joint being welded.
2. Reference line — always drawn horizontally; every other part of the symbol is tied to it.
3. Dashed line — used in ISO 2553 to distinguish the two sides of the joint; not used in AWS A2.4. It's omitted entirely if the weld is symmetrical on both sides.
4. Weld symbol — other side — a symbol placed above the dashed line applies to the side of the joint opposite the one the arrow points to.
5. Weld symbol — arrow side — a symbol placed below the solid reference line applies to the side of the joint the arrow points to.
6. Size / dimension — a figure (e.g. leg length or throat thickness) placed to the left of the weld symbol, on the reference line.
7. Length and pitch — for intermittent welds, the weld length and the spacing between welds, placed to the right of the symbol.
8. Tail — an optional open fork at the end of the reference line, used to reference a welding process code, specification, or other note that doesn't have its own place on the symbol. It's omitted when there's nothing to reference.

Because the same-shaped symbol can sit above or below the line, the same basic weld type symbol can call up a weld on either side of the joint, or both, just by where it's drawn relative to the reference and dashed lines.

BASIC WELD SYMBOLS

BASIC WELD SYMBOLS — ISO 2553 & AWS A2.4
WELD TYPE	SYMBOL	STANDARDS	NOTES
Fillet		ISO 2553 & AWS A2.4	Same symbol in both standards
Square Groove		ISO 2553 & AWS A2.4	Same symbol in both standards
V Groove		ISO 2553 & AWS A2.4	Same symbol in both standards
Bevel Groove		ISO 2553 & AWS A2.4	Same symbol in both standards
U Groove		ISO 2553 & AWS A2.4	Same symbol in both standards
J Groove		ISO 2553 & AWS A2.4	Same symbol in both standards
Flare-V Groove		ISO 2553 & AWS A2.4	Same symbol in both standards
Flare-Bevel Groove		ISO 2553 & AWS A2.4	Same symbol in both standards
Plug / Slot		ISO 2553 & AWS A2.4	ISO 2553 refers to this as a "slot" weld; AWS A2.4 covers plug and slot with the same symbol
Spot / Projection		ISO 2553 & AWS A2.4	Same symbol in both standards
Seam		ISO 2553 & AWS A2.4	Same symbol in both standards
Backing		ISO 2553 & AWS A2.4	Same symbol in both standards
Surfacing		ISO 2553 & AWS A2.4	Same symbol in both standards
Edge		ISO 2553 & AWS A2.4	Same symbol in both standards

SUPPLEMENTARY SYMBOLS

These are added to a basic weld symbol, on or around the reference line, to give extra instructions about how or where the weld should be made.

SUPPLEMENTARY WELD SYMBOLS — ISO 2553 & AWS A2.4
SYMBOL MEANING	SYMBOL	STANDARDS	NOTES
Weld All Around		ISO 2553 & AWS A2.4	Circle placed at the junction of the arrow and reference line; same symbol in both standards
Field Weld		ISO 2553 & AWS A2.4	Filled flag at the junction of the arrow and reference line; same symbol in both standards
Contour — Flush		ISO 2553 & AWS A2.4	Straight line above the weld symbol; same symbol in both standards
Contour — Convex		ISO 2553 & AWS A2.4	Outward curved line above the weld symbol; same symbol in both standards
Contour — Concave		ISO 2553 & AWS A2.4	Inward curved line above the weld symbol; same symbol in both standards
Melt-Through		ISO 2553 & AWS A2.4	Filled lens shape on the side opposite the basic symbol; same symbol in both standards
Backing Bar		ISO 2553 & AWS A2.4	A letter (R for removable, or similar) is often added inside the symbol in AWS A2.4 to show whether the backing is removed after welding
Consumable Insert		ISO 2553 & AWS A2.4	Shown as a filled square sitting in the root of a groove weld symbol; same symbol in both standards

These are simplified reference renderings intended to help identify each symbol at a glance. For the exact proportions, dimensions and full rules on combining symbols, arrows, tails and reference lines, always refer to ISO 2553 or AWS A2.4 directly.

WELD FACE (CONTOUR) SYMBOLS — NEAR SIDE & FAR SIDE

The three contour symbols above — flat, convex and concave — describe the finished shape of the weld surface rather than the weld type itself, so they're always added alongside a basic weld symbol rather than used on their own.

• Flat face — the weld is finished flush with the surrounding material.
• Convex face — the weld surface bulges outward, above the surrounding material.
• Concave face — the weld surface is hollowed, sitting below the surrounding material.

Because a weld symbol can apply to the near side (arrow side) or far side (other side) of a joint, the contour symbol is drawn touching whichever reference line represents that side — the table below shows all six combinations.

WELD FACE SYMBOLS — NEAR SIDE & FAR SIDE
SIDE	FLAT FACE	CONVEX FACE	CONCAVE FACE
Near side (arrow side)
Far side (other side)