Reference / Weld symbols
Weld Symbols Explained
A weldment drawing without weld symbols is a suggestion. The shop still has to decide what weld goes where, and because it carries the risk it decides generously. You pay for that in weld metal, distortion and hours.
Anatomy of the symbol
Six parts. Everything else hangs off these.
- ArrowPoints at the joint. On a joint where one member is prepared, the arrow breaks towards the member to be bevelled.
- Reference lineAlways horizontal, whatever direction the arrow runs.
- Weld symbolThe shape saying what kind of weld. The chart below has them all.
- SizeTo the left of the symbol. Leg length on AWS drawings, often throat on ISO drawings. Say which.
- Length and pitchTo the right. Absence means a continuous weld, which is the expensive default.
- TailCarries the procedure reference, the process, the inspection requirement or a note.
The weld symbols
Drawn sitting on the reference line, as they appear on a drawing.
| Symbol | Name | What it means | When it is used |
|---|---|---|---|
| Fillet | A triangular weld in the corner of a tee, lap or corner joint. | The default joint on weldments. No edge preparation, so it is the cheapest weld on the drawing. | |
| Square groove | A butt joint with no bevel, welded through the gap between square edges. | Thin plate only, where the arc can reach the root without a prepared edge. | |
| V groove | A butt joint with both edges bevelled to form a V. | Full penetration from one side on medium plate. More weld metal than a fillet and more shrinkage. | |
| Bevel groove | One member bevelled, the other left square. | Where only one side can be prepared, or a tee that needs penetration. The arrow breaks towards the member to be prepared. | |
| U groove | A butt joint with a curved preparation. | Thick plate. Uses less weld metal than a V of the same depth, at a higher preparation cost. | |
| J groove | One member prepared with a curved groove, the other square. | Thick tee joints needing penetration where a full V is wasteful. | |
| Plug or slot | A hole or slot in the top member filled with weld to join it to the one beneath. | Attaching overlapping plate where an edge fillet cannot reach or would be in the way. | |
| Back or backing | A weld on the far side of the joint, usually after gouging the root. | Used with a groove weld to ensure a sound root on double sided joints. |
Supplementary symbols
These sit on or beside the weld symbol and change what the shop has to do.
| Symbol | What it means | Cost note |
|---|---|---|
| Weld all round | A circle at the junction of arrow and reference line. Every face of the joint gets welded. | Quick to draw and expensive to make. Use only where the joint must truly be sealed all around. |
| Field weld | A flag at the junction. The weld is made at the installation site, not in the shop. | Rare on machined weldments, common on structures shipped in sections. |
| Flush contour | A straight line across the weld symbol. The weld face is finished flush. | Required where the weld sits under a machined face or a mating surface. It is a grinding or machining operation and a cost line. |
| Convex contour | A curved line over the weld symbol. The face is left or made convex. | Normal as-welded condition for a fillet. |
The five omissions that cost you money
In order of how often we see them.
Weld size
Fillet volume rises with the square of the leg. An 8 mm fillet where 5 mm was needed is roughly two and a half times the weld metal and the shrinkage.
Which side
Symbols placed without thinking about arrow side produce joints welded both sides when one was enough.
Length and pitch
Continuous is the default. An intermittent weld where the loading allows it uses a fraction of the metal and distorts far less.
Contour and finish
A weld under a machined face has to be dressed flush. If the drawing does not say so, it will not be.
Tacks and attachments
Whether tack welds, lifting lugs and strongbacks stay or are removed and blended is a real line item.
There is a longer version of this with worked examples in the guide on weld symbols on a weldment drawing, and the geometry side is covered in GD&T on welded and machined parts.
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