Welding Symbols on Drawings — How to Read Them
Welding symbols on engineering drawings follow AWS A2.4:2020. The reference line, arrow, weld symbol, and optional tail convey weld type, size, side, and process. Whether on a structural steel drawing, a fabrication blueprint, or a shop drawing, the same four-element system applies.
The Four Elements of a Welding Symbol
Every welding symbol on a structural drawing or fabrication blueprint is built from four elements defined in AWS A2.4:2020:
1. Reference Line
The reference line is always drawn horizontally, regardless of the joint orientation on the drawing. It is the backbone of the welding symbol. All other elements attach to it. The reference line connects the arrow to the weld symbol and any supplementary symbols. When two reference lines appear (a rare but valid notation), the first applies to the arrow-side weld; the second to a subsequent operation.
2. Arrow
The arrow connects the reference line to the actual joint on the drawing. It always touches the joint it describes. For bevel and J-groove welds, a broken arrow (bent before touching the joint) indicates which member receives the joint preparation. The break is on the side of the arrow pointing to the member to be beveled.
3. Weld Symbol
The weld symbol is the small graphic sitting on or above/below the reference line that indicates the weld type. A right triangle = fillet weld. An open-V = V-groove. Two curves = seam weld. The symbol sits below the reference line for the arrow side of the joint; above for the other side. When both sides show a symbol, weld both sides.
4. Tail
The tail is the V-shaped element at the left end of the reference line, opposite the arrow. It is omitted when not needed. When present, it carries the WPS reference number, the applicable welding process (SMAW, FCAW, GMAW), or a note such as "AWS D1.1." On blueprints and shop drawings, the tail most often references the welding procedure by number.
Arrow Side vs. Other Side
The most common source of confusion when reading welding symbols on drawings is the arrow side / other side convention. AWS A2.4:2020 Section 6.1 defines it precisely:
Arrow side means the same side of the joint as the arrow points to. The weld symbol appears below the reference line. If you trace the arrow to the joint, the weld goes on the face the arrow touches.
Other side means the opposite face of the joint from the arrow. The weld symbol appears above the reference line.
When the same symbol appears on both sides of the reference line, weld both sides of the joint with the same parameters. When the symbols differ (e.g., different sizes), each side has its own dimensions read from the respective position.
On a structural steel blueprint or shop drawing, this convention means you can specify a 3/8" fillet on the arrow side and a 1/4" fillet on the other side in a single, compact notation on the drawing.
Reading Dimensions on a Drawing
Dimension placement on a welding symbol follows a fixed convention per AWS A2.4:2020:
Left of the weld symbol = weld size. For a fillet weld, this is the leg length. For a groove weld, the depth of preparation appears in parentheses (e.g., (5/8)) and the effective throat, when specified, follows in parentheses after the depth.
Right of the weld symbol = length and pitch for intermittent welds. Written as length-pitch: 3-12 means 3-inch weld segments at 12-inch center-to-center spacing. If no length appears to the right, the weld is continuous for the full joint length.
For CJP (complete joint penetration) groove welds, no size dimension appears on the symbol. The designation CJP or the absence of a dimension signals complete penetration. The WPS controls how it is achieved.
Common Drawing Conventions
Several supplementary symbols frequently appear on structural steel drawings and fabrication blueprints alongside the weld symbol:
CJP with no size dimension — a groove weld symbol with no number to the left means complete joint penetration is required. No size dimension is needed because the full thickness must be fused. The inspector verifies via UT or RT where required.
Field weld flag — a solid triangular flag at the junction of the reference line and arrow indicates the weld must be made in the field (at the erection site), not in the fabrication shop. This is critical information on structural drawings because it affects weld procedure, inspection scheduling, and logistics.
Weld-all-around circle — a small circle at the reference line / arrow junction means the weld must be made completely around the joint perimeter. Common for tube-to-plate connections and pipe penetrations. The circle is distinct from the field weld flag, which is a filled triangle.
Broken arrow for bevel joints — when the arrow bends before reaching the joint, the member it points toward receives the joint preparation (bevel or J-groove). This prevents ambiguity on asymmetric joints where only one member is prepared.