Introduction: The Language of Welding
Welding symbols are the standardized graphical language used on engineering drawings to communicate welding requirements precisely. Understanding these symbols is essential for welders, inspectors, and engineers to ensure that welds are made correctly according to design specifications.
This comprehensive guide covers the AWS (American Welding Society) welding symbol system, the most widely used standard in North America, teaching you how to read and interpret welding blueprints with confidence.
The Basics of Welding Symbols
Components of a Welding Symbol
- Reference Line: Horizontal line, foundation of the symbol, arrow connects to joint, information placed above/below
- Arrow: Points to joint location, can point either direction, breaks at reference line, leader line to joint
- Tail: Optional component, contains additional info, specification reference, process or other notes
Basic Weld Symbols
- Fillet Weld: Right triangle shape, most common weld type, triangular cross-section, used for T-joints and laps
- Groove Weld: Various shapes, butt joint welds, complete penetration, partial penetration
- Plug and Slot Welds: Circle or rectangle, filled holes, shear connections, specific dimensions
- Spot and Projection: Circle or cross, resistance welding, specific spacing, size indicated
Fillet Weld Symbols
Basic Fillet Weld
Symbol Placement: Below reference line equals arrow side, above reference line equals other side, both sides equals symbol both places.
Size Dimension: Leg dimension in inches or mm, placed to left of symbol, 1/4" or 6mm typical.
Intermittent Fillet Welds
- Chain Intermittent: Welds on both sides aligned, pitch dimension shown, length of each weld, spacing between
- Staggered Intermittent: Welds offset, better distribution, same dimension format, pitch and length
Contour and Finish
- Flush Contour: Straight line across symbol, flush with surface, grinding required
- Convex Contour: Curved line above, rounded face, natural profile, no finish required
- Concave Contour: Curved line below, slightly hollow, special technique
Groove Weld Symbols
Groove Types
Square Groove
Two parallel lines, no edge preparation, thin material, partial penetration.
V-Groove
V-shape, single bevel each side, most common groove, 60° typical angle.
Bevel Groove
L-shape, single bevel, one side prepared, other side square.
U and J Grooves
Curved bottom, both sides for U, curved one side for J, less common.
Supplementary Symbols
Common Supplementary Symbols
- Weld All Around: Circle at arrow bend, weld continues around, box or cylindrical shape
- Field Weld: Flag at arrow bend, weld done in field, not in shop, erection weld
- Melt-Through: Solid circle on reference line, root reinforcement required, visible from back side
- Backing and Spacers: Rectangle symbol below, remains in place, supports root pass
Dimensioning Welds
Standard Dimension Placement
- Left Side: Weld size (leg or throat), groove depth, spot diameter, essential dimension
- Right Side: Weld length, pitch (intermittent), number of spots, extent of welding
- Other Dimensions: Angle of bevel, root opening, radius (U-groove), contour radius
Process Designation
Common Processes
- SMAW: Shielded Metal Arc
- GMAW: Gas Metal Arc
- FCAW: Flux Cored Arc
- GTAW: Gas Tungsten Arc
- SAW: Submerged Arc
Common Specifications
- AWS D1.1 (Structural)
- AWS D1.2 (Aluminum)
- ASME Section IX
- API 1104 (Pipeline)
- Military specs
Reading Complete Welding Symbols
Example Interpretations
1/4" fillet weld, both sides, continuous, flush finish, field weld
V-groove, 60°, 1/8" root opening, complete penetration, back gouge required, grind flush
3/16" fillet, 2" long welds, 6" pitch, staggered, both sides
Common Mistakes
Symbol Errors
- Arrow Side Confusion: Most common error, check arrow direction, verify symbol placement
- Dimension Misreading: Size vs. length, pitch vs. length, metric vs. inch
- Contour Misunderstanding: Flush vs. convex, finish requirements, grinding specified
Drawing Interpretation
- Scale Errors: Not checking scale, assuming full size, detail views, section views
- View Confusion: Front vs. top, section views, detail callouts, hidden lines
Conclusion
Welding symbols provide a precise, standardized method for communicating welding requirements on engineering drawings. Mastering this symbolic language is essential for welders, inspectors, and engineers to ensure that welded structures meet design specifications and perform safely in service.
By understanding the components of welding symbols, their proper placement, and standard dimensioning practices, you can accurately interpret welding blueprints and produce quality welds that meet all specified requirements.
Always check the arrow direction, verify symbol placement (above/below reference line), confirm dimensions, and consult specifications when in doubt.
