UK Welding Procedure — BS EN 1090-2 Specification for Structural Steelwork
Welding procedure requirements for UK structural steelwork per BS EN 1090-2:2018 Execution Classes 2-4. Covers welding procedure specification (WPS), welding procedure qualification (WPQR), preheat requirements, filler metal selection, and welding processes commonly used for S275 and S355 steel in UK fabrication.
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Welding Procedure Framework per BS EN 1090-2
BS EN 1090-2 requires that all structural welding be performed using qualified welding procedures. The system comprises:
- WPS — Welding Procedure Specification (the written procedure)
- WPQR — Welding Procedure Qualification Record (test evidence)
- Welders certification — Individual welder qualification per BS EN ISO 9606-1
Welding Processes for UK Structural Steel
| Process | ISO 4063 Number | UK Application | Typical Wire/Electrode |
|---|---|---|---|
| MAG (Metal Active Gas) | 135 | Default for UK building frames | G4Si1 (EN ISO 14341), G3Si1 for S275 |
| MIG (Metal Inert Gas) | 131 | Stainless, aluminium structural | Appropriate filler per EN ISO |
| MMA (Manual Metal Arc) | 111 | Site welding, tacking, repairs | E42 (EN ISO 2560) for S355 |
| SAW (Submerged Arc) | 121 | Bridge girders, heavy plate | S2 wire + flux per EN ISO 14174 |
| TIG (Tungsten Inert Gas) | 141 | Root runs for butt welds in pipe | W2Si (EN ISO 636) |
| Flux-cored (FCAW) | 136 | Heavy section site welding | T 42 2 M M 1 H5 (EN ISO 17632) |
Filler Metal Selection
| Base Material | Process | Filler Metal Standard | Typical Grade | Min Yield |
|---|---|---|---|---|
| S275 | MAG | BS EN ISO 14341-A | G3Si1 | 420 MPa |
| S275 | MMA | BS EN ISO 2560-A | E38 0 | 380 MPa |
| S355 | MAG | BS EN ISO 14341-A | G4Si1 | 470 MPa |
| S355 | MMA | BS EN ISO 2560-A | E42 0 | 420 MPa |
| S355 | SAW | BS EN ISO 14171-A | S3Si | 470 MPa |
| S355 (N/Z) | MAG | BS EN ISO 16834-A | G69 4 M21 | 690 MPa |
Filler metals are selected to be overmatching (yield strength ≥ base metal yield strength) or matching (at least equal). Undermatching is only permitted with specific design verification per EN 1993-1-8.
Preheat Requirements per BS EN 1011-2
Preheat temperature depends on CEV, plate thickness, and hydrogen level:
| CEV | t ≤ 20 mm | 20 < t ≤ 40 mm | 40 < t ≤ 60 mm | t > 60 mm |
|---|---|---|---|---|
| ≤ 0.40 | None | 50°C | 75°C | 100°C |
| 0.40-0.45 | 50°C | 75°C | 100°C | 125°C |
| 0.45-0.50 | 75°C | 100°C | 125°C | 150°C |
| > 0.50 | 100°C | 125°C | 150°C | 175°C |
For S355J2 with CEV = 0.45 % and t = 25 mm: minimum preheat = 75°C.
Welding Parameters — Typical UK Values
MAG (135) — Short-circuit transfer:
| Plate t (mm) | Filler size (mm) | Current (A) | Voltage (V) | Travel speed (mm/min) | Heat input (kJ/mm) |
|---|---|---|---|---|---|
| 6 | 1.0 | 150-180 | 19-21 | 350-450 | 0.5-0.7 |
| 10 | 1.2 | 200-260 | 22-25 | 300-400 | 0.8-1.2 |
| 15 | 1.2 | 240-300 | 24-27 | 250-350 | 1.0-1.5 |
| 25 | 1.2 | 280-340 | 26-29 | 200-300 | 1.5-2.0 |
Heat input per pass: Q = η × U × I / v × 60 (J/mm), where η = 0.8 for MAG.
UK NA Modifications
The UK NA to BS EN 1090-2 confirms:
- Default execution class for building frames: EXC2
- WPS qualification must be to BS EN ISO 15614-1 (destructive testing)
- Preheat per BS EN 1011-2 with CEV from mill certificate
- Filler metals must have minimum CVN of 27 J at -20°C for J2 subgrades
- Hardness limit for welded joints: ≤ 350 HV for EXC2, ≤ 320 HV for EXC4
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 standard welding process for UK building steelwork?
The standard welding process for UK structural steelwork is MAG welding (ISO 4063-135) using G4Si1 filler wire for S355 and G3Si1 for S275. MAG provides good productivity and quality for workshop fabrication. For site welding, MMA (111) is still common due to its portability and tolerance to weather conditions. SAW (121) is used for heavy plate girder fabrication in specialist bridge workshops.
What preheat is required for welding S355J2 in UK fabrication?
Preheat for S355J2 depends on the CEV and plate thickness. For CEV ≤ 0.45 % (typical for S355J2 ≤ 40 mm): no preheat for t ≤ 20 mm, 75°C for 20 < t ≤ 40 mm, 100°C for 40 < t ≤ 60 mm. For higher CEV values or thicker sections, preheat increases per BS EN 1011-2 Table C.2. The actual CEV from the mill certificate should be used. All preheat must be verified with temperature-indicating crayons or digital thermometers per BS EN 1090-2.
What filler metal is used for welding S355 steel?
For S355:S275 fabricated in the UK, the standard MAG filler is G4Si1 per BS EN ISO 14341-A (yield strength ≥ 420 MPa, Charpy 47 J at -20°C). For MMA (site welding), the standard electrodes are E42 grade per BS EN ISO 2560-A. For SAW (girder fabrication), S3Si wire with an agglomerated flux per BS EN ISO 14174 is standard. For S355NL (fine-grain), use G69 filler per BS EN ISO 16834-A to match toughness.
What is a WPS and when is it required for UK steelwork?
A Welding Procedure Specification (WPS) is a written document defining the welding parameters (process, filler metal, preheat, interpass temperature, welding current, voltage, travel speed, heat input, post-weld heat treatment if required). A WPS is required for all structural welding in EXC2, EXC3, and EXC4 per BS EN 1090-2. Each WPS must be supported by a WPQR (Welding Procedure Qualification Record) demonstrating that the procedure produces acceptable mechanical properties. The WPQR must be to BS EN ISO 15614-1 for destructive testing or BS EN ISO 15613 for pre-production welding tests.
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.