[ WELDING SYMBOLS · REFERENCE ]
How to read welding symbols
A welding symbol packs a lot into a few lines: what kind of weld, which side of the joint, how big, how long, how it is finished, and how it is made. Read it in a fixed order and it is quick.
- Weld symbol vs welding symbol
- The weld symbol is the shape (triangle, V). The welding symbol is the whole thing: line, arrow, symbols, sizes and tail
Read it in this order
- 1. The arrow: it points at the joint. A break in the arrow points to the member that gets the bevel or preparation. See reference line and arrow.
- 2. The side: AWS, below the line is the arrow side and above is the other side. ISO system A, the solid line is the arrow side and the dashed line the other side. See other side weld.
- 3. The weld symbol: the shape tells you the type, a triangle for a fillet, a V for a V groove, and so on.
- 4. The size: to the left of the symbol. AWS fillets give the leg; ISO fillets give a (throat) or z (leg). Groove welds give the depth and effective throat.
- 5. Length and spacing: to the right of the symbol. No length means the weld runs the full length of the joint.
- 6. Groove details: root opening inside the symbol, groove angle beside it.
- 7. Supplementary symbols: weld all around, field weld, backing and contour.
- 8. The tail: process, procedure or note. See tail.
A worked example
An AWS symbol with a triangle below the line, 6 to its left, 50-150 to its right, a flag at the junction and GMAW in the tail reads: a 6 mm fillet weld on the arrow side, intermittent, 50 mm long at 150 mm centres, made in the field with gas metal arc welding.
The same weld on an ISO system A drawing reads: a triangle on the solid line, z6 to its left, the number of welds, x 50 (100) to its right, for example 10 x 50 (100), a flag, and 135 in the tail. The 100 is the gap between welds, not the pitch.
Finish letters
A letter beside a contour symbol says how the finish is achieved:
| Letter | Finish method |
|---|---|
| C | Chipping |
| G | Grinding |
| H | Hammering |
| M | Machining |
| P | Planishing |
| R | Rolling |
| U | Unspecified |
Inspection letters
Nondestructive examination is often shown on or next to the welding symbol with standard letters:
| Letters | Method |
|---|---|
| VT | Visual testing |
| PT | Penetrant testing |
| MT | Magnetic particle testing |
| RT | Radiographic testing |
| UT | Ultrasonic testing |
On a project, every weld that needs inspection is tracked against its joint, with the inspection records as evidence before the system can be completed. See the ITR guide.
Frequently asked questions
What is the difference between a weld symbol and a welding symbol?
The weld symbol is the shape for the type of weld, such as a triangle for a fillet. The welding symbol is the full symbol: reference line, arrow, weld symbols, sizes, supplementary symbols and tail.
Which side does the arrow point to?
The arrow side is the side of the joint the arrow touches. The other side is the opposite side of the same joint.
What do the numbers on the right of a weld symbol mean?
The length of the weld and, for intermittent welds, the spacing: pitch (centre to centre) in AWS, distance between welds in ISO.
What does a flag on a welding symbol mean?
A field weld or site weld: the weld is made at installation, not in the shop.
- In production since 2014
- Thousands of daily users
- On MODEC FPSO projects since 2016
The symbols on this page were drawn by Deskely and are free to use. Standards are revised and every project issues its own legend sheets, which take precedence.