UK Weld Symbols — BS EN 22553 Standard Reference for Structural Steel Detailing

Reference chart of standard weld symbols per BS EN 22553 (identical to ISO 2553) for UK structural steelwork detailing. Covers fillet welds, butt welds, plug welds, edge welds, and the reference line system used in UK fabrication drawings per BS EN 1090-2 and BS 8888 engineering drawing standards.

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BS EN 22553 (ISO 2553) Weld Symbol System

The UK standard for weld symbols is BS EN 22553, which is identical to ISO 2553. The system uses a reference line, arrow line, and tail to convey complete welding instructions.

Basic Symbol Elements

     (Supplementary symbols)    (Flag for site weld)
                      \              |
     Reference line ---+-------------+
     Arrow line ------/              |
                      (Weld symbols)

The reference line has an arrow side and a other side. Symbols above the reference line indicate welds on the other side of the arrow; symbols below indicate arrow-side welds.

Basic Weld Symbols

Supplementary Symbols

Weld Dimensioning — Fillet Welds

The standard dimensioning format for fillet welds on UK drawings:

        8        (leg length — throat = leg/√2)
        △
        150      (weld length)

• Leg length (a): 6 mm, 8 mm, 10 mm, 12 mm (standard UK sizes)
• Effective throat (a): leg length × 0.707
• Intermittent fillet weld: 100 △ 200 (100 mm weld, 200 mm centres)
• Staggered intermittent: Symbol on both sides of reference line, staggered

Butt Weld Dimensioning

        Y
        ∨
        150

• Y indicates preparation angle (typically 45-60° for single V)
• Root gap: Typically 2-4 mm per BS EN 1011-2
• Back gouging required for double-sided butt welds

UK Practice per BS EN 1090-2

UK fabrication drawings to BS EN 1090-2 Execution Classes 2-4 must include:

1. Weld symbol per BS EN 22553
2. Weld size (throat thickness a for fillets, depth for butts)
3. Weld length and spacing (for intermittent welds)
4. Execution class reference (EXC2, EXC3, EXC4)
5. NDT requirements (visual, UT, MPI if required)
6. Welding process (135 = MAG, 111 = MMA, 121 = SAW)

Common UK Fillet Weld Specifications

The minimum fillet weld size per BS EN 1090-2 is 3 mm (for t ≤ 5 mm) and typically 6 mm for main structural connections. The maximum fillet weld size per pass is approximately 8 mm throat before multiple passes are required.

Design Resources

• UK Steel Grades Reference — EN 10025-2 grade selection for UK projects
• UK Steel Mechanical Properties — fy, fu, and elongation tables
• UK Universal Beam and Column Sizes — UB/UC section dimensions and properties
• UK Bolt Capacity Tables — Class 8.8 and 10.9 bolt resistance
• UK Beam Design Guide — EN 1993-1-1 flexure, shear, and LTB
• UK Connection Design Guide — EN 1993-1-8 bolted and welded joints
• All UK Steel Design References — complete library

Frequently Asked Questions

What is the difference between BS EN 22553 and the old BS 499 weld symbols?

BS EN 22553 (ISO 2553) replaced BS 499:Part 2 for weld symbols on UK drawings. The ISO system uses the reference line with the weld symbol placed below (arrow side) or above (other side). BS 499 used a similar concept but with different symbol positions and additions. The transition was completed in the early 2000s. Most current UK fabrication drawings use BS EN 22553. Older UK drawings (pre-2000) may still use BS 499 — the symbols are similar but the reference line convention differs slightly.

How is a site weld indicated on a UK fabrication drawing?

A site weld is indicated by a flag symbol (▲) at the junction of the reference line and arrow. Without the flag, the weld is assumed to be a workshop weld. Site welds are typically minimised in UK practice because they are more expensive, subject to weather conditions, and require on-site NDT. UK fabrication drawings specify site welds only for connections that cannot be welded in the workshop (e.g., splices in continuous columns, roof apex connections).

What does the tail of a BS EN 22553 weld symbol contain?

The tail contains supplementary information: welding process (e.g., 135 for MAG, 111 for MMA), execution class (EXC2, EXC3, EXC4), NDT requirements, and weld sequence. If no supplementary info is needed, the tail is omitted. On UK drawings, the tail typically includes the process number per ISO 4063 and the execution class.

What fillet weld throat size is standard for UK beam-to-column connections?

For standard UK simple connections (fin plates, partial-depth end plates), the fillet weld throat is typically 6-8 mm for S355 material. The throat thickness a ≥ 0.5 × t (thinner plate) for full strength, though a = 6 mm is the practical minimum for main connections. For moment-resisting end plate connections, full-penetration butt welds (single V or double V) are typically specified rather than fillet welds, particularly when the design requires the weld to develop the full strength of the connected section.

Related Pages

• EN 1993 Steel Design Overview
• European Steel Properties
• EN 1993 Beam Design Guide
• EN 1993 Column Buckling
• EN 1990 Load Combinations
• UK Steel Chemical Composition
• UK Steel Charpy Values

Educational reference only. All design values are per BS EN 1993-1-1:2005 + UK National Annex and BS EN 10025-2:2019. Verify all values against the current editions of the standards and the applicable National Annex for your project jurisdiction. Designs must be independently verified by a Chartered Structural Engineer registered with the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE). Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent professional verification.