Standard Welding Symbol Standards
Welding symbols communicate weld requirements on engineering drawings. Two main standards:
- AWS A2.4 (American Welding Society) — used in USA, Americas, oil/gas industry
- ISO 2553 (International) — used in Europe, Asia, many international projects
This guide focuses on AWS symbols (most common in international engineering).
The Welding Symbol Structure
A complete welding symbol has:
<-- Tail (reference/spec)
/
----||---- <-- Reference line (horizontal)
\
<-- Arrow (points to joint)
Elements that may appear:
- Reference line (always present, horizontal)
- Arrow line (points to joint location)
- Basic weld symbol (triangle for fillet, V for V-groove, etc.)
- Dimensions (size, length, pitch)
- Supplementary symbols (field weld, all-around, etc.)
- Tail (reference to specification or process)
Basic Weld Symbols
| Symbol | Shape | Weld Type |
|---|---|---|
| △ (triangle) | Right triangle | Fillet weld (most common) |
| V | V shape | V-groove weld |
| √ (bevel) | One-sided V | Bevel groove |
| U | U shape | U-groove |
| J | J shape | J-groove |
| □ (square) | Two parallel lines | Square groove |
| ○ (circle) | Circle at reference/arrow junction | Plug/slot weld |
| (two vertical bars) | ||
| ☆ (flare-V) | Flared V | Flare bevel/V |
Fillet Welds (Most Common)
Fillet welds are triangular welds at T-, lap, and corner joints. The symbol is a right triangle.
Dimensioning Fillet Welds
Size: Leg length in mm (or inches) placed to the LEFT of the triangle.
- 6mm fillet = "6" left of triangle
- Equal-leg fillets are standard; unequal legs noted as two numbers
Length: Weld length in mm placed to the RIGHT of the triangle.
- "100" means 100mm long weld
Pitch/intermittent spacing: Center-to-center spacing of intermittent welds after a hyphen.
- "6-100-200" = 6mm fillet, 100mm long, every 200mm
Examples
6△— 6mm fillet, continuous, arrow side△150— fillet weld, 150mm long (size in separate note or both sides)8△ 8▲— 8mm fillet both sides (other side is mirror)6△200-400— 6mm intermittent fillet, 200mm long every 400mm staggered or chain
Groove Welds
Groove welds fill a prepared joint between two pieces:
| Type | Symbol | Preparation |
|---|---|---|
| Square | □ | No bevel, gap only; for t ≤ 6mm |
| V-groove | V | Both sides beveled; common for pipe |
| Bevel groove | √ (slant) | One side beveled; arrow points to beveled piece |
| U-groove | U | Both sides concave (J preparation) |
| J-groove | J | One side concave |
Groove Weld Dimensions
- Depth of bevel (left of symbol): how deep the bevel is cut
- Groove weld size (in parenthesis): required throat (usually = material thickness)
- Root opening: gap between parts; shown inside symbol or note
- Groove angle: angle of bevel; shown above/below symbol
Example: 20° V ¾ means V-groove with 20° angle, ¾" groove weld size, arrow side.
Supplementary Symbols
| Symbol | Location | Meaning |
|---|---|---|
| Solid circle at junction | At arrow/reference junction | Weld all around the joint |
| Flag (triangle) at angle | At junction | Field weld (site, not shop) |
| Concave curve over symbol | Above/below weld symbol | Concave finish |
| Convex curve over symbol | Convex finish | |
| Flush/flat bar | Finished flat (machined/ground) | |
| Melt-through (filled-in back) | Complete joint penetration from other side | |
| Backing bar symbol | Rectangle behind groove | Backing strip used |
Tail Reference — Process and Specification
The tail at the end of the reference line notes:
- Welding process: SMAW (stick), GMAW (MIG), GTAW (TIG), FCAW, SAW
- Specification: e.g., "WPS-P1" = Welding Procedure Specification P1
- Acceptance criteria: e.g., "UT per AWS D1.1"
Example: 6△ / SMAW WPS-101 = 6mm fillet using SMAW per WPS 101.
Common Joint Types
| Joint | Weld Type | Typical Symbol |
|---|---|---|
| Butt joint | V- or bevel-groove CJP | V with CJP note |
| T-joint | Fillet both sides | Double fillet triangle |
| Lap joint | Fillet weld ends | Fillet each end |
| Corner joint | Fillet or partial groove | |
| Edge joint | Edge weld (parallel lines) |
Common Welding Abbreviations
| Abbreviation | Meaning |
|---|---|
| CJP | Complete Joint Penetration (full penetration groove weld) |
| PJP | Partial Joint Penetration |
| GMAW | Gas Metal Arc Welding (MIG) |
| GTAW | Gas Tungsten Arc Welding (TIG) |
| SMAW | Shielded Metal Arc Welding (stick) |
| FCAW | Flux-Cored Arc Welding |
| SAW | Submerged Arc Welding |
| WPS | Welding Procedure Specification |
| PQR | Procedure Qualification Record |
| WPQ | Welder Performance Qualification |
| NDE | Non-Destructive Examination |
| UT | Ultrasonic Testing |
| RT | Radiographic Testing |
| MT | Magnetic Particle Testing |
| PT | Penetrant Testing |
Weld Size vs Strength
Fillet weld strength depends on effective throat:
For E70 electrodes (most common for structural steel), allowable shear ≈ 140 MPa (20 ksi).
Worked Example
A 6mm fillet weld 100mm long can carry:
- Throat = 6 × 0.707 = 4.24 mm
- Shear area = 4.24 × 100 = 424 mm²
- Allowable force = 424 × 140 = 59,400 N ≈ 60 kN per 100mm
Pipe Welding Symbols
For pipe butt welds (circumferential joints):
- V-groove or U-groove symbol with "all around" circle
- Often specifies root pass (TIG hot pass), fill, cap processes
- "100% RT" means full radiographic examination required
- Typical for process piping: GTAW root + SMAW fill/cap
Summary
Welding symbols follow AWS A2.4 or ISO 2553 standards. Reference line with symbols above/below identifies weld type and which side. Fillet welds (triangle) are most common — size to the left, length to the right. Groove welds specify bevel depth, angle, and CJP/PJP. Supplementary symbols denote field weld, all-around, finish, and backing. Always consult the project welding legend and WPS for process and electrode requirements. Incorrectly read symbols lead to welds on wrong side or wrong size — double-check arrow-side/other-side convention.