Weld preheat calculator
Preheat slows the cooling of a weld so hydrogen can escape before the heat-affected zone cracks. The CET method adds four terms: the steel’s alloy content (CET), the plate thickness, the consumable’s diffusible hydrogen and the heat input. A steel at CET 0.28 % in 30 mm plate, welded with an H5 consumable at 1.5 kJ/mm, needs about 61 °C. Enter the mill analysis, the thickness, the hydrogen level and the arc settings for yours.
- Minimum preheat Tp
- CET
- 0.280%
- CE (IIW), the mill certificate's CEV
- 0.39%
- Heat input Q
- Arc energy (k = 1)
- 1.88kJ/mm
- Calculated value
How it’s calculated
Tp = 697·CET + 160·tanh(d/35) + 62·HD^0.35 + (53·CET − 32)·Q − 328 (°C; BS EN 1011-2:2001 Annex C, Method B). CET = C + (Mn + Mo)/10 + (Cr + Cu)/20 + Ni/40. Q = k·U·I·60 / (1000·v) kJ/mm, v in mm/min. CE (IIW) = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. Valid for yield strength up to 1000 MPa and CET 0.20–0.50 %, d 10–90 mm, HD 1–20 ml/100 g, Q 0.5–4.0 kJ/mm. Here: 195.2 + 111.2 + 108.9 − 25.7 − 328 = 61.5 °C.
Minimum preheat (°C) by thickness and hydrogen, this steel and heat input
| Plate d (mm) | HD 3 | HD 5 | HD 10 | HD 15 |
|---|---|---|---|---|
| 10 | none | none | 25 | 46 |
| 15 | none | none | 45 | 67 |
| 20 | none | 33 | 63 | 85 |
| 25 | 31 | 49 | 79 | 100 |
| 30 | 44 | 62 | 92 | 113 |
| 40 | 63 | 81 | 111 | 132 |
| 50 | 76 | 93 | 123 | 145 |
| 60 | 83 | 101 | 131 | 152 |
| 75 | 89 | 106 | 136 | 158 |
| 90 | 91 | 109 | 139 | 160 |
“none”: at or under 20 °C. HD 3, 5, 10 and 15 are the H3, H5, H10 and H15 consumable classes.
Arc energy or heat input?
Arc energy is volts times amps over travel speed. Heat input takes off what the process loses: submerged arc is the reference at 1.0, MIG/MAG, flux-cored and stick 0.8, TIG and plasma 0.6. European procedures record heat input; US codes record the arc energy, so the same weld reads higher on an ASME or AWS procedure. The calculator shows both.