[ WELDING SYMBOLS · STANDARD ]
ISO 2553 welding symbols
ISO 2553 is the international standard for welding symbols on drawings, used across Europe, the Middle East and Asia, and on most international projects. Its system A adds a dashed identification line: a symbol on the solid line is on the arrow side, a symbol on the dashed line on the other side.
- Full title
- ISO 2553, Welding and allied processes, Symbolic representation on drawings, Welded joints
- Current edition
- ISO 2553:2019, also published in Europe as EN ISO 2553
- Two systems
- System A uses a solid reference line and a dashed identification line. System B uses a single line and the AWS placement
- Fillet sizes
- a for the throat thickness, z for the leg length, written before the value, such as a5 or z7
- Processes
- Process numbers from ISO 4063 in the tail, such as 111, 135 and 141
Groove welds ISO 2553
About groove welds- Square groove weldSquare butt weld
- V groove weldSingle-V butt weld
- Bevel groove weldSingle-bevel butt weld
- U groove weldSingle-U butt weld
- J groove weldSingle-J butt weld
- Flare-V groove weldFlare-V butt weld
- Flare-bevel groove weldFlare-bevel butt weld
- Double-V groove weldDouble-V butt weld (X weld)
- Double-bevel groove weldDouble-bevel butt weld (K weld)
- V groove with broad root faceSingle-V butt weld with broad root face (Y)
Fillet, plug, spot and seam welds ISO 2553
About fillet, plug, spot and seam weldsSupplementary symbols ISO 2553
About supplementary symbolsParts of a welding symbol ISO 2553
About parts of a welding symbolThe ISO rules in short
- System A: a symbol on the solid line is on the arrow side, a symbol on the dashed line on the other side. The dashed line can be drawn above or below the solid line.
- For symmetrical welds, such as an X weld or a double fillet, the dashed line is left out.
- Fillet sizes carry their letter: a for throat, z for leg. Without the letter you cannot tell which is meant.
- Intermittent welds are written as the number of welds, their length and the distance between them, for example 3 x 50 (100).
- Backing strips are marked M (permanent) or MR (removable) in a rectangle.
- The tail carries the ISO 4063 process number and can carry the quality level, the working position and the filler metal.
System B exists so that drawings for Pacific and American markets can follow the AWS placement inside the same standard. Check the title block or the general notes to see which system a drawing uses. Compare the two on AWS vs ISO welding symbols.
Common ISO 4063 process numbers
| ISO 4063 | Process | AWS letters |
|---|---|---|
| 111 | Manual metal arc welding | SMAW |
| 121 | Submerged arc welding with one wire electrode | SAW |
| 131 | MIG welding with solid wire | GMAW |
| 135 | MAG welding with solid wire | GMAW |
| 136 | MAG welding with flux-cored wire | FCAW |
| 141 | TIG welding with solid filler | GTAW |
| 21 | Resistance spot welding | RSW |
| 22 | Resistance seam welding | RSEW |
| 311 | Oxy-acetylene welding | OAW |
Frequently asked questions
What is ISO 2553?
The international standard for symbolic representation of welded joints on drawings. The current edition is ISO 2553:2019, published in Europe as EN ISO 2553.
What does the dashed line mean on an ISO welding symbol?
In system A, a weld symbol on the dashed identification line is on the other side of the joint. A symbol on the solid line is on the arrow side.
What is the difference between a and z on an ISO fillet weld?
a is the throat thickness and z is the leg length. For an equal-leg fillet the leg is about 1.4 times the throat, so a5 and z5 are very different welds.
What is the difference between ISO 2553 system A and system B?
System A uses a solid reference line and a dashed identification line. System B uses one line and places arrow side welds below it, as AWS A2.4 does.
- 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.