Fillet Weld Symbol Explained
The fillet weld symbol is a standardized graphical notation used on engineering drawings to communicate the size, length, spacing, and location of a fillet weld. It is defined by AWS A2.4 (Standard Symbols for Welding, Brazing, and Nondestructive Examination) and ISO 2553 in international practice. To read the fillet weld symbol matters for fabricators, welders, and inspectors working on piping and structural projects.
Fillet Weld Symbol Anatomy
The welding symbol consists of a reference line, an arrow, and specific elements placed in defined positions.
| Element | Position | Meaning |
|---|---|---|
| Reference line | Horizontal line | Baseline for all symbol information |
| Arrow | Points to joint | Identifies the joint to be welded |
| Weld symbol (triangle) | Below reference line | Fillet weld on the arrow side |
| Weld symbol (triangle) | Above reference line | Fillet weld on the other side |
| Size (left of symbol) | Number before triangle | Leg size in mm or inches |
| Length (right of symbol) | Number after triangle | Weld length |
| Pitch (after length) | Hyphenated number | Center-to-center spacing for intermittent welds |
| Tail | Opposite end from arrow | Contains process, specification, or notes |
| All-around symbol | Circle at arrow/reference junction | Weld extends around the full joint perimeter |
| Field weld flag | Filled triangle at junction | Weld to be performed in the field, not in the shop |
When the Fillet Weld Symbol Is Used
Fillet weld symbols appear on piping isometric drawings, structural steel details, and fabrication shop drawings wherever a triangular-cross-section weld is required. Typical applications include socket weld connections, slip-on flange attachments, pipe support attachments, reinforcing pads on branch connections, and structural T-joints.
Arrow Side vs Other Side
The position of the triangle relative to the reference line tells the welder which side of the joint receives the fillet weld:
| Placement | Rule (AWS A2.4) | Rule (ISO 2553) |
|---|---|---|
| Arrow side | Symbol below reference line | Symbol below reference line (same) |
| Other side | Symbol above reference line | Symbol above reference line, dashed |
| Both sides | Symbols above and below | Symbols above and below |
In AWS practice, the arrow side is always below the reference line. In ISO 2553 (2013 edition), the other-side symbol may appear on a dashed line above or below the reference line depending on the convention system (A or B) adopted by the project.
Reading a Fillet Weld Symbol: Example
A symbol showing “6” to the left of a triangle below the reference line and “50-100” to the right means:
- 6 mm fillet weld leg size
- On the arrow side
- 50 mm weld length
- 100 mm center-to-center pitch (intermittent weld)
If the same information appears both above and below the reference line, the weld is on both sides of the joint with the same size and spacing.
Supplementary Symbols
| Symbol | Meaning |
|---|---|
| Convex contour (arc above) | Weld face must be convex |
| Flush contour (straight line) | Weld face must be ground flush |
| Concave contour (arc below) | Weld face must be concave |
| ”G” at contour | Grinding required |
| ”M” at contour | Machining required |
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