5.1 Anatomy of a Welding Symbol (AWS A2.4)
Key Takeaways
- Welding symbols are defined by AWS A2.4 and consist of reference line, arrow, weld symbol, tail, and dimensions
- Arrow side/other side convention: below reference line = arrow side, above = other side
- Weld size is placed to the LEFT of the weld symbol; weld length to the RIGHT
- Flag at junction = field weld; circle at junction = weld-all-around
- Tail contains supplementary info: welding process, specification number, WPS reference
- Welding symbols account for ~10% of Part A questions — practice until the convention is automatic
5.1 Anatomy of a Welding Symbol (AWS A2.4)
Welding symbols are a standardized graphical language defined by AWS A2.4 — Standard Symbols for Welding, Brazing, and Nondestructive Examination. Every CWI must be fluent in reading welding symbols on drawings and blueprints.
Components of a Complete Welding Symbol
A welding symbol has eight major components:
| Component | Location | Purpose |
|---|---|---|
| Reference line | Horizontal line — always present | The "backbone" of the symbol; all information is read relative to it |
| Arrow | Points from reference line to the joint | Identifies the joint location; one end connects to the reference line |
| Weld symbol | Above or below the reference line | Indicates the type of weld (fillet, groove, plug, etc.) |
| Tail | Opposite end of reference line from arrow | Contains supplementary info (process, specification, WPS number) |
| Dimensions | Near the weld symbol | Weld size, length, pitch, number of welds |
| Supplementary symbols | Various locations | Contour, finish method, field weld, weld-all-around, backing/spacer |
| Finish symbols | Above contour symbol | G (grind), C (chip), M (machine), R (roll), H (hammer), U (unspecified) |
| NDE symbols | On or near reference line | Type of examination required |
Arrow Side vs. Other Side Convention
This is the most critical concept in welding symbol interpretation:
- Arrow side = the side of the joint that the arrow points to
- Other side = the opposite side of the joint from the arrow
- Weld symbol BELOW the reference line = weld on the arrow side
- Weld symbol ABOVE the reference line = weld on the other side
- Weld symbols BOTH above and below = weld on both sides
Memory Aid: Think "Below = By the arrow" — the weld symbol below the reference line corresponds to the arrow side of the joint.
Weld Symbols (Shape Characters)
| Symbol | Weld Type |
|---|---|
| △ (triangle) | Fillet weld |
| V | V-groove (single or double) |
| ½V (one straight side) | Bevel-groove |
| U | U-groove |
| J | J-groove |
| ‖ (parallel lines) | Square-groove (no bevel) |
| ○ (circle) in rectangle | Plug or slot weld |
| Rectangle with radiused ends | Seam weld |
| Small circle | Spot weld |
Supplementary Symbols
| Symbol | Meaning |
|---|---|
| Flag (attached to junction of reference line and arrow) | Field weld — weld is made in the field, not in the shop |
| Circle around junction | Weld-all-around — weld is continuous around the entire joint |
| Flat line on top of weld symbol | Flush contour |
| Convex arc on top | Convex contour |
| Concave arc on top | Concave contour |
| Filled rectangle | Backing (below reference line = arrow side) |
| Open rectangle | Spacer |
Reading Dimensions on Welding Symbols
For a fillet weld symbol with dimensions:
3/8 (weld size — leg dimension)
----△----
4 - 8 (4" weld length, 8" center-to-center pitch)
- Left of the weld symbol = weld size (leg dimension for fillet, depth for groove)
- Right of the weld symbol = weld length
- Pitch = center-to-center spacing of intermittent welds (shown after a dash)
For a groove weld symbol:
- Left of weld symbol (inside parentheses) = groove weld size (effective throat or depth of groove)
- Left of weld symbol (without parentheses) = depth of bevel preparation
- Groove angle shown on the weld symbol itself
- Root opening = shown inside the weld symbol
For the Exam: Welding symbols represent 10% of Part A questions (~15 questions). The arrow-side/other-side convention is the most frequently tested concept. Practice reading complete welding symbols until the convention becomes automatic.
On a welding symbol, a fillet weld symbol placed BELOW the reference line indicates the weld is on:
A flag symbol at the junction of the arrow and reference line indicates:
What does a circle drawn around the junction of the arrow and reference line indicate?
On a welding symbol, where is the weld size (leg dimension for fillet welds) placed?