S355 preheat temperature by thickness
S355 needs no preheat in thin plate, but from around 10–15 mm upwards a minimum preheat is required to avoid hydrogen cracking. The table below is calculated with EN 1011-2 Annex C method B for a typical S355J2 analysis.
Preheat table for S355J2
Assumptions: typical S355J2 composition (C 0.17, Mn 1.40, Cr 0.05, Mo 0.02, Ni 0.05, Cu 0.15 %), giving CET = 0.32; heat input Q = 1.2 kJ/mm; plate thickness d is the thickness of each plate in a butt joint.
| d (mm) | HD 5 (H5) | HD 10 (H10) | HD 15 (H15) |
|---|---|---|---|
| 10 | 33 °C | 63 °C | 84 °C |
| 15 | 53 °C | 83 °C | 104 °C |
| 20 | 71 °C | 101 °C | 122 °C |
| 25 | 87 °C | 116 °C | 138 °C |
| 30 | 100 °C | 129 °C | 151 °C |
| 40 | 119 °C | 149 °C | 170 °C |
| 50 | 131 °C | 161 °C | 182 °C |
| 60 | 138 °C | 168 °C | 189 °C |
| 80 | 145 °C | 175 °C | 196 °C |
Values at or below 20 °C mean no preheat is needed at normal workshop temperature. In cold conditions the plate should still be warmed to remove moisture.
What changes the preheat
- Hydrogen level: going from H5 to H10 adds about 30 °C. Basic electrodes and solid MAG wire are usually H5; rutile electrodes and some flux-cored wires are higher.
- Heat input: in method B, higher heat input lowers the preheat. Dropping to 0.8 kJ/mm raises it by roughly 5–6 °C for S355.
- Composition: the actual CET from your 3.1 certificate can differ noticeably from the typical value; enter it in the calculator.
- Joint type: fillet welds and highly restrained joints may need more; EN 1011-2 uses a combined thickness for some joint types.
The formula
CET = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40 Tp [°C] = 697·CET + 160·tanh(d/35) + 62·HD^0.35 + (53·CET − 32)·Q − 328
Method B is valid for CET 0.20–0.50, d 10–90 mm, HD 1–20 ml/100 g and Q 0.5–4.0 kJ/mm. The preheat temperature calculator applies these limits, uses your own analysis and shows the result for every thickness at once. The heat input for your parameters comes from the welding heat input calculator.
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