— Welding Reference
Weld Symbol Basics (AWS A2.4)
A weld symbol has a horizontal reference line with an arrow pointing to the joint. The side the arrow touches is the "arrow side"; the opposite side is the "other side." A symbol drawn below the reference line means weld the arrow side; above means weld the other side; on both means weld both sides. An optional tail at the far end holds process/spec references.
Reference line = the horizontal line; arrow = points to the joint; symbol below the line = weld on the arrow side (as shown here, a fillet weld).
| Weld Type | Symbol Shape |
|---|---|
| Fillet | Right triangle sitting on the reference line; the perpendicular leg is always drawn on the left, regardless of arrow direction |
| Square groove | Two short parallel lines, perpendicular to the reference line, open at the ends |
| V-groove | A "V" open away from the reference line; both members symmetrically beveled (a double-V forms an X/hourglass shape) |
| Bevel groove | One straight vertical line (square edge) + one angled line, forming a half-V; only one member is beveled, arrow points to it |
| U-groove | A "U" (curved bottom) open away from the reference line; both members have a radiused (J-shaped) edge prep |
| J-groove | A "J" shape — one square (vertical) side + one radiused side; only one member is prepped |
| Plug/Slot | Rectangle sitting on the reference line (weld fills a round hole = plug, elongated hole = slot) |
| Spot | Plain circle, typically straddling the reference line |
| Seam | A circle with two parallel lines through it, extending past the circle on both sides |
Common Weld Joint Types
| Joint Type | Typical Weld Type | Notes |
|---|---|---|
| Butt joint | Groove (square, V, bevel, U, J) | Two pieces in the same plane; full-penetration groove welds give maximum strength — standard for plate/pipe structural or pressure work |
| Lap joint | Fillet (also plug/slot) | Two pieces overlapped; easy fit-up, no edge prep, but stress concentration at the overlap — common on sheet metal |
| T-joint | Fillet (or partial/full-penetration groove for heavy loads) | One member perpendicular to another; extremely common in structural framing |
| Corner joint | Fillet (open corner) or groove (closed/flush corner) | Two edges meeting at ~90°; common in sheet-metal boxes/frames/enclosures |
| Edge joint | Edge weld (surface/flange weld along adjoining edges) | Weakest joint type — not for load-bearing work; used for sealing thin sheet edges |
See the Weld Strength calculator to size a fillet weld's throat and check shear stress against an applied load.
Filler Metal Selection
AWS stick-electrode numbering (e.g. E7018): "E" = electrode; first two/three digits × 1,000 psi = minimum tensile strength (E70 → 70,000 psi min.); next-to-last digit = welding position; last digits together = flux coating type + current/polarity.
| Filler | Spec | Notes |
|---|---|---|
| ER70S-6 | AWS A5.18 | Solid MIG wire, 70 ksi min. tensile, highest deoxidizer content in the 70S family — tolerates mill scale/light rust. De facto all-purpose mild-steel MIG wire |
| E6010 | AWS A5.1 | Cellulose-sodium coating, deep penetration, DCEP only; classic pipe root-pass rod, all-position |
| E6011 | AWS A5.1 | Cellulose-potassium coating, same deep penetration as E6010 but runs on AC; general-purpose/farm-repair rod |
| E7018 | AWS A5.1 | Low-hydrogen iron-powder coating, AC or DCEP; requires clean base metal and dry storage. Standard for code-quality structural steel |
| 4043 | AWS A5.10 | Al-Si filler; better flow/wetting, lower crack sensitivity, smoother bead. Turns dull/dark gray after anodizing |
| 5356 | AWS A5.10 | Al-Mg filler; higher strength, much better color match after anodizing. Not recommended for sustained service above ~150°F (Mg>3% risks stress-corrosion cracking) |
| 308L | AWS A5.9 | Matching low-carbon filler for 304/304L stainless — avoids carbide precipitation/sensitization |
| 316L | AWS A5.9 | Matching filler for 316/316L stainless — carries Mo to preserve pitting/chloride corrosion resistance |
Welding Process Comparison
| Process | Typical Use | Portability/Cost | Shielding |
|---|---|---|---|
| SMAW (Stick) | Field repair, structural/maintenance, outdoor/windy or dirty conditions | Highest portability, lowest cost (no gas, no wire feeder) | Flux coating decomposes to shield the arc |
| GMAW (MIG) | Production/shop fabrication, thin-to-medium sheet & plate, automotive | Moderate cost; needs gas cylinder + wire feeder | External shielding gas (Ar/CO2 blends or straight CO2) |
| GTAW (TIG) | Precision work, thin material, aluminum/stainless/exotic alloys, pipe root passes | Higher cost, least portable, typically shop-based | Inert gas, typically pure Argon |
| FCAW (Flux-core) | Heavy structural steel, thick material, outdoor/high-deposition production | Moderate cost; self-shielded variant is portable and wind-tolerant | Self-shielded or gas-shielded variant |