UK Weld Electrodes — EN ISO 2560 & EN ISO 14341 Guide

Welding electrode selection for UK structural steelwork follows EN ISO 14341 (MAG wire electrodes) and EN ISO 2560 (MMA electrodes). The electrode must provide weld metal strength at least matching the parent metal, with adequate toughness for the service temperature and loading conditions.

Code Reference: EN ISO 14341, EN ISO 2560, BS EN 1090-2

Electrode Classification Systems

MAG electrodes (EN ISO 14341): G 42 4 M21 3Si1

• G = Gas-shielded solid wire electrode
• 42 = Minimum yield strength (420 MPa)
• 4 = Charpy V-notch impact 47J at 0°C (Z = 47J at -20°C, D = 47J at -30°C)
• M21 = Shielding gas (M21 = Ar + 15-25% CO₂; C1 = 100% CO₂)
• 3Si1 = Chemical composition (silicon/manganese content)

MMA electrodes (EN ISO 2560): E 42 4 B 4 2 H10

• E = Covered electrode (manual metal arc)
• 42 = Minimum yield strength (420 MPa)
• 4 = Charpy 47J at 0°C
• B = Basic covering (rutile R, cellulosic C)
• 4 = Efficiency class
• 2 = Welding position (2 = all positions except vertical down)
• H10 = Hydrogen class (≤ 10 ml/100g)

Electrode Selection by Steel Grade

Toughness Requirements

Hydrogen Control (BS EN 1090-2)

Typical Wire Electrode Diameters (MAG)

Worked Example — Electrode Selection for S355J2 Portal Frame

Given:

• Portal frame in S355J2 (fy = 355 MPa, required toughness 27J at -20°C)
• Execution class EXC3, site welding
• Plate thickness: 20-30 mm (flanges)

Step 1 — Select electrode strength: Matching: yield strength ≥ 355 MPa, tensile ≥ 510 MPa MAG: G 46 Z M21 3Si1 (fy ≥ 460 MPa, Charpy 47J at -20°C) MMA: E 46 4 B 4 2 H5 (fy ≥ 460 MPa, basic covering, H5 hydrogen class)

Step 2 — Hydrogen control (EXC3): Preheat required for t > 25 mm: 75-100°C minimum Electrode conditioning: basic electrodes baked at 300°C for 2 hours Storage in heated quiver (80-120°C) on site

Step 3 — Check weld metal overmatching: Weld metal strength (460 MPa yield) > parent metal (355 MPa yield) This ensures the weld is stronger than the parent — the plastic hinge forms in the parent metal, not the weld.

Design Resources

• UK Weld Capacity — Fillet and butt weld design
• UK Steel Properties — Parent metal properties
• UK Connection Design — Welded connection design
• UK Steel Grades — Grade comparison
• All UK References

Frequently Asked Questions

What welding electrodes are used for UK structural steel?

For S275 structural steel: MAG wire G 42 4 M21 3Si1 (EN ISO 14341) or MMA electrode E 42 4 RR 1 2 (EN ISO 2560). For S355: MAG G 46 4 M21 3Si1 or MMA E 46 4 B 4 2 H10. For S355J2 (low-temperature toughness): MAG G 46 Z M21 3Si1 or MMA E 46 4 B 4 2 H5 with hydrogen control. Electrode designation is standardised across Europe, so UK electrodes are compatible with European supply chains.

What is the difference between MAG and MMA welding?

MAG (Metal Active Gas) welding — also called MIG — uses a continuous wire feed with gas shielding (Ar + CO₂). It is the most common method in UK fabrication workshops (80%+ of structural welds) due to high deposition rate and ease of automation. MMA (Manual Metal Arc) uses a consumable electrode with flux coating. It is preferred for site welding, overhead welds, and smaller fabrications. MMA is slower but more portable and tolerant of wind and surface contamination.

What hydrogen class is required for UK structural welds?

BS EN 1090-2 (Execution of steel structures) requires: EXC1: H15 (no special control). EXC2: H10 (basic electrodes baked). EXC3: H5 (strict hydrogen control including preheat). EXC4: H5 with mandatory preheat verification. Hydrogen control prevents hydrogen-assisted cold cracking (HACC) in heat-affected zones. For S355 steel above 25 mm thickness, preheat of 75-150°C is typically specified for EXC3.

How do you select electrodes for dissimilar steel grades?

When welding S355 to S275, the electrode should match the weaker parent metal (S275). The weld metal strength should be at least equal to the weaker part. For S355 to S275: use G 42 4 (S275 level). For S460 to S355: use G 46 4 (S355 level or slightly higher). EN 1993-1-8 Clause 4.2 states that the design strength of the weld is based on the weaker connected part. The electrode strength should not significantly overmatch (> 50 MPa above the weaker part) to avoid HAZ cracking in the lower-strength steel.

What post-weld heat treatment is required for UK steel structures?

Per BS EN 1090-2, post-weld heat treatment (PWHT) is required for: (a) quenched and tempered steels above 50 mm thickness, (b) all thicknesses of S460+ when specified by the design, (c) for fatigue-loaded details requiring stress relief, and (d) when dimensional stability is critical. PWHT temperature: 550-650°C for 1 hour per 25 mm thickness. For most UK building structures in S275/S355 below 40 mm thickness, PWHT is not required.

Weld Design Methods

Fillet Weld Design

Fillet welds are the most common weld type in structural steel construction. The design strength is calculated based on the weld throat dimension and effective length.

For AISC 360 LRFD:

• φRn = φ × 0.60 × FEXX × (0.707w) × L × (1.0 + 0.50 sin¹·⁵θ)
• Where φ = 0.75, FEXX = electrode classification strength, w = weld leg size

For EN 1993-1-8:

• Fw,Rd = fu / √3 × a / (βw γM2)
• Where a = weld throat thickness, βw = correlation factor (0.80-1.0 depending on steel grade)

Design Procedure for Fillet Welds

1. Determine the required weld size from the applied load
2. Select the appropriate electrode (E70XX for steels with Fu ≤ 480 MPa, E80XX for higher strength)
3. Calculate the weld capacity per unit length
4. Determine the required weld length
5. Check minimum and maximum weld size limitations
6. Verify weld termination details (return welds, end returns)

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Frequently Asked Questions

What is the recommended design procedure for this structural element?

The standard design procedure follows: (1) establish design criteria including applicable code, material grade, and loading; (2) determine loads and applicable load combinations; (3) analyze the structure for internal forces; (4) check member strength for all applicable limit states; (5) verify serviceability requirements; and (6) detail connections. Computer analysis is recommended for complex structures, but hand calculations should be used for verification of critical elements.

How do different design codes compare for this calculation?

AISC 360 (US), EN 1993 (Eurocode), AS 4100 (Australia), and CSA S16 (Canada) follow similar limit states design philosophy but differ in specific resistance factors, slenderness limits, and partial safety factors. Generally, EN 1993 uses partial factors on both load and resistance sides (γM0 = 1.0, γM1 = 1.0, γM2 = 1.25), while AISC 360 uses a single resistance factor (φ). Engineers should verify which code is adopted in their jurisdiction.

Reference only. Verify all values against the current edition of EN ISO 14341, EN ISO 2560, and BS EN 1090-2. This information does not constitute professional engineering advice.