Weld Symbols — Engineering Reference
AWS A2.4 welding symbol guide: fillet, V-groove, bevel, plug and slot symbols. Arrow/other-side, all-around, field weld, intermittent dimensions explained.
Overview
Welding symbols are the standard graphical language used on structural drawings to communicate weld type, size, length, location, process, and inspection requirements between the engineer, detailer, and fabricator. The governing standard in North America is AWS A2.4 (Standard Symbols for Welding, Brazing, and Nondestructive Examination). In Australia, AS 1101.3 applies, while European practice follows EN ISO 2553.
A welding symbol consists of a reference line (horizontal), an arrow pointing to the joint, and various elements placed above, below, or at the ends of the reference line. The side of the reference line indicates whether the weld is on the arrow side (below the line) or the other side (above the line). A flag at the junction of the reference line and arrow indicates a field weld (to be performed on site rather than in the shop).
Anatomy of a welding symbol
The components of a complete welding symbol per AWS A2.4 are:
- Reference line — the horizontal line that carries all weld information. Multiple reference lines can be stacked for multi-pass or sequential welds.
- Arrow — points to the joint location on the drawing. The arrow side of the joint corresponds to symbols placed below the reference line.
- Weld symbol — the geometric shape indicating the weld type (triangle for fillet, V for groove, etc.), placed on the appropriate side of the reference line.
- Dimensions — weld size appears to the left of the symbol, weld length to the right. For intermittent welds, length and pitch are shown as length-pitch (e.g., 3-6 means 3 in. long at 6 in. center-to-center).
- Tail — optional; contains supplementary information such as the welding process (e.g., SMAW, GMAW), electrode specification (E70XX), or a reference to a welding procedure specification (WPS).
- Finish symbols — C (chipping), G (grinding), M (machining) indicate the method of surface finishing after welding.
Common weld type symbols
| Weld Type | Symbol Shape | Typical Application |
|---|---|---|
| Fillet weld | Triangle (right-angle) | Lap joints, tee joints, skewed connections. Most common structural weld. |
| Single-V groove | V shape | Butt joints requiring full or partial penetration from one side. |
| Single-bevel groove | Half-V | Tee joints with CJP or PJP from one side; beam-to-column flange connections. |
| Double-V groove | Two V shapes (both sides) | Thick butt joints welded from both sides for balanced distortion. |
| Flare-bevel groove | Curved half-V | HSS-to-plate connections where one member has a curved surface. |
| Plug / slot | Rectangle with dimensions | Connecting overlapping plates where edge access is limited. |
| Back / backing weld | Semicircle | Applied to the root side after completing a groove weld, or as a backing pass. |
Supplementary symbols
- All-around symbol — a circle at the arrow/reference line junction indicates the weld continues completely around the joint (e.g., around the perimeter of an HSS connection).
- Field weld flag — a solid flag (triangle) at the arrow/reference line junction means the weld is to be made in the field, not in the shop.
- Melt-through symbol — a filled semicircle on the opposite side indicates complete joint penetration is required with visible root reinforcement.
- Spacer symbol — a rectangle on the reference line indicates a backing bar or spacer is specified.
- Contour symbols — flush (straight line), convex (arc), or concave (inverted arc) indicate the required weld face profile after finishing.
AWS vs. ISO symbol differences
| Feature | AWS A2.4 | EN ISO 2553 |
|---|---|---|
| Arrow side placement | Below reference line | Below reference line (Method A) or above (Method B) |
| Other side placement | Above reference line | Above reference line (Method A) or below (Method B) |
| Dimension placement | Size left, length right of symbol | Size left, length right (same) |
| All-around circle | At arrow/line junction | At arrow/line junction (identical) |
| Staggered intermittent | Z-pattern notation | Similar, with pitch indicated |
| Tail usage | Process, electrode, WPS | Similar supplementary data |
Method A in ISO 2553 matches the AWS convention. Method B (used in some European countries) reverses the arrow/other-side convention, which can cause confusion on international projects. Always confirm which convention the project uses.
Reading weld symbols — practical example
A symbol showing a right triangle below the reference line with "5/16" to its left and "6-12" to its right means: 5/16 in. fillet weld, 6 in. long, spaced at 12 in. center-to-center (intermittent), on the arrow side. If the same triangle also appears above the reference line with matching dimensions, it is a staggered intermittent fillet weld on both sides.
For a single-bevel groove weld with a 45-degree included angle and 1/4 in. root opening, the symbol shows a half-V below the reference line with "45°" written inside the V and "1/4" at the root. If a tail note says "E70", the electrode is E70XX (70 ksi tensile strength).
Common mistakes to avoid
- Confusing arrow side and other side — placing the weld symbol on the wrong side of the reference line causes the weld to be placed on the wrong side of the joint in fabrication. On international projects using ISO 2553 Method B, the convention is reversed from AWS.
- Omitting the all-around symbol — when a weld must wrap continuously around a member (e.g., an HSS brace to gusset), forgetting the all-around circle results in only three sides being welded, leaving a critical unwelded face.
- Missing the field weld flag — if a weld must be done on site (e.g., beam-to-column moment connections), the field weld flag must be shown. Without it, the fabricator may attempt to shop-weld a joint that must be field-connected.
- Incomplete groove weld designation — groove welds require the included angle, root opening, and root face to be specified. Omitting any of these forces the fabricator to guess, potentially producing an inadequate or over-welded joint.
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Related references
- Minimum Weld Size
- Weld Electrodes
- How to Verify Calculations
- weld joint types
- weld group capacity
- Weld Inspection
- Weld size selection reference
Disclaimer
This page is for educational and reference use only. It does not constitute professional engineering advice. All design values must be verified against the applicable standard and project specification before use. The site operator disclaims liability for any loss arising from the use of this information.