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

Filler Metal Selection

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:

For S355J2 with CEV = 0.45 % and t = 25 mm: minimum preheat = 75°C.

Welding Parameters — Typical UK Values

MAG (135) — Short-circuit transfer:

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

Worked Example — WPS for UK Portal Frame Eaves Connection

Problem: Prepare a Welding Procedure Specification for the eaves moment connection of a UK portal frame. Members: S355J2 533x210x82 UB rafter welded to S355J2 254x254x107 UC column via full-strength butt weld. Rafter flange 16.5 mm, column flange 20.5 mm. EXC2 per BS EN 1090-2. Ambient shop temperature minimum 8°C.

Step 1 — Base Metal Verification per BS EN 10025-2: Both members S355J2: CEV ≤ 0.45 for t ≤ 40 mm. Mill certificates confirm CEV: rafter 0.40, column 0.42. Both acceptable. Charpy: 27 J at -20°C verified.

Step 2 — WPS Parameters per BS EN ISO 15609-1: Process: 135 (MAG) with M21 shielding gas (Ar + 15-25% CO₂ per BS EN ISO 14175). Wire: G 46 5 M21 (1.2 mm), fy ≥ 460 MPa, Charpy 47 J at -50°C per BS EN ISO 14341. Joint: Single-bevel partial penetration — 45° bevel on rafter flange, 6 mm root face, 3 mm root gap. Position: PB (horizontal-vertical), shop welding.

Step 3 — Preheat per BS EN 1011-2: CEV (column) = 0.42, t = 20.5 mm. Per BS EN 1011-2 Annex C:

• Minimum preheat: 50°C (hydrogen scale D, CEV ≤ 0.43, t ≤ 30 mm)
• For highly restrained T-joint at eaves: increase by 25°C → 75°C
• Interpass: 150°C-250°C per BS EN 1090-2 Table 16

Step 4 — Welding Parameters: Root run: 220 A, 24 V, travel 300 mm/min. Fill runs: 260 A, 27 V, travel 350 mm/min. Heat input (fill): Q = 0.8 × 27 × 260 / (350/60 × 1000) = 0.8 × 7020 / 5833 = 0.96 kJ/mm. Within recommended 1.0-2.5 kJ/mm range for S355 per BS EN 1011-2 Table C.1.

Step 5 — WPS Qualification per BS EN ISO 15614-1: WPQR test plate: 20 mm S355J2, single-bevel butt weld, PB position. Required tests per BS EN ISO 15614-1 Clause 8:

• 2 transverse tensile tests (BS EN ISO 6892-1) — Rm ≥ 470 MPa
• 4 side bend tests (BS EN ISO 5173) — 180° bend, no defect > 3 mm
• 1 Charpy set at -20°C (BS EN ISO 9016) — HAZ and weld metal, ≥ 27 J
• 1 hardness survey (BS EN ISO 9015-1) — ≤ 350 HV10
• 1 macrograph (BS EN ISO 17639) — full fusion, no cracks

Step 6 — Production Control per BS EN 1090-2 Clause 7.5:

• Welding sequence: balanced about neutral axis to control distortion
• Back gouging: carbon arc gouging to sound metal before second side
• Visual inspection: 100% to BS EN ISO 17637, acceptance Level C per BS EN ISO 5817
• Weld identification: unique ID, welder stamp, date per BS EN 1090-2 Clause 12

Result: WPS qualified for S355J2 eaves connection, 16.5-20.5 mm thickness. MAG process (135), G 46 5 M21 wire, 75°C preheat. WPQR supports EXC2 per BS EN 1090-2.

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

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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.