Steel and preheat
Minimum preheat temperature, CET method (BS EN 1011-2 Annex C method B)
- where
- minimum preheat temperature (°C)
- carbon equivalent CET (%)
- plate thickness (mm)
- weld metal diffusible hydrogen (ml/100 g)
- heat input (kJ/mm)
Explain this equation
Calculates the minimum preheat temperature to avoid hydrogen cracking, using the BS EN 1011-2 method B equation. Use it when writing or checking a welding procedure.
Each term pushes the preheat up or down. A higher CET means a harder heat-affected zone, so more preheat. Thicker plate pulls heat away faster; tanh makes that effect level off for very thick plate. More hydrogen in the weld metal (H_D) needs more preheat to let it escape. A higher heat input Q slows cooling and so reduces the preheat needed. The −328 is a constant from fitting the equation to test results.
The equation is an empirical fit to cracking tests, valid for CET 0.20–0.50%, thickness 10–90 mm, hydrogen 1–20 ml/100 g and heat input 0.5–4.0 kJ/mm.
Sense check: CET 0.35, 30 mm plate, 5 ml/100 g hydrogen and 1.5 kJ/mm gives about 116 °C. Dropping to H5 consumables from H15 can save a lot of preheat.
Watch out: a result below room temperature means no preheat is needed by this method, but never weld on cold, wet or frosted steel.
Estimates the minimum preheat to avoid hydrogen cracking from CET, thickness, consumable hydrogen level and heat input, using the BS EN 1011-2 method B equation.
Enter your values to see the result.
Good to know
d is the thickness of the thicker plate being joined. HD is the consumable’s diffusible hydrogen in ml/100 g of deposited metal (from the data sheet: H5 ≈ 5, H10 ≈ 10). Q is heat input (k × arc energy). Method A of BS EN 1011-2 uses CE(IIW), combined thickness and a hydrogen scale (A–E) on charts instead; the two methods can give different answers, so use the one your WPS refers to.
Common mistake
Using the plate thickness from one side only for a fillet weld, or using arc energy instead of heat input. Also forgetting that higher hydrogen (damp rods, rusty plate) raises preheat a lot.
Limits
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, for structural steels with yield strength up to about 1000 N/mm². It does not cover restraint beyond normal, which may need more preheat. Minimum interpass is normally the same as preheat.
Sources
- BS EN 1011-2:2001 Welding – Recommendations for welding of metallic materials – Part 2: Arc welding of ferritic steels (Annex C: CE and CET preheat methods; Annex D: cooling time t8/5)
- Dillinger welding calculator help: CET, EN 1011-2 preheat formula and validity range (CET 0.2–0.5 %, d 10–90 mm, HD 1–20 ml/100 g, Q 0.5–4.0 kJ/mm), t8/5 2D/3D equations, transition thickness and shape factors F2/F3
- TWI FAQ: What is the difference between the various carbon equivalent formulae used in relation to hydrogen cracking? (CE(IIW), Pcm, CET in EN 1011-2)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the welding procedure specification (WPS), BS EN ISO 15614/9606, BS EN 1090, BS EN 1993 and manufacturers’ data. Structural welds need qualified welders and engineered designs.