Preheat Temperature Calculator — EN 1011-2 Method B
Minimum preheat to avoid hydrogen-induced cold cracking, from the carbon equivalent CET, the combined thickness of the joint, the consumable's diffusible hydrogen and the heat input. Type a real grade and the CET is derived from that grade's own specified composition. A real GET form: computes correctly with JavaScript off.
EN 1011-2 Annex C.3, method B — non-alloyed and low-alloy steels only. Guidance for preparing a welding procedure, never a substitute for a qualified WPS.The update failed. Your entries have been kept — please try again.
Read this before you use the number
Too little preheat causes hydrogen-induced cold cracking, and cold cracks appear hours or days after welding — long after the weld has been looked at and accepted. This calculator reproduces one published method inside its stated limits; it does not know your restraint, your joint geometry, your consumable's real hydrogen level or your ambient conditions. Use it to prepare and sanity-check a welding procedure. The number that governs production is the one in a qualified WPS.
How method B arrives at a temperature
Four things decide whether a weld cracks in the cold: how hardenable the steel is, how fast the joint pulls heat away, how much hydrogen the process puts into the weld metal, and how much energy the arc leaves behind. Method B puts one term against each — CET for hardenability, combined thickness for the heat sink, HD for hydrogen, Q for arc energy — and returns the temperature at which cooling is slow enough for that hydrogen to diffuse out before it can do damage.
One detail is worth stating because it is widely published wrong: the thickness term is tanh(d / 35), which RISES with thickness. A thicker section drains heat faster and therefore needs MORE preheat, not less. Several well-ranking calculators use tanh(35 / d), which inverts the physics and under-predicts preheat exactly where the joint is heaviest and the consequences worst. This engine implements the standard's text.
Where the method stops
Method B is validated for CET 0.20–0.50 %, combined thickness 10–90 mm, HD 1–20 ml/100 g and heat input 0.5–4.0 kJ/mm. Outside those windows this calculator refuses and names the bound you crossed, because the expression keeps returning a number long after it has stopped predicting anything. It also does not cover stainless, austenitic or high-alloy steels: enter a stainless grade and the carbon equivalent itself will be refused on chromium, which is the method telling you it is the wrong tool.
Preheat temperature — frequently asked
Can I weld without preheat if the result is negative or very low?
A result at or below ambient means the formula predicts no preheat requirement for those four inputs — it does not mean welding is unconditionally safe. Restraint, moisture, base-metal temperature below about 5 °C and thick or rigid assemblies all argue for preheat that this formula never saw. The result feeds a WPS; the WPS decides.
Why is the CET taken from the maximum permitted composition and not the middle?
Because a heat delivered at the top of the specified range is fully compliant — and fully hardenable. Sizing preheat on a midpoint would leave every compliant heat above that midpoint under-protected, and under-protection is the direction in which cracks happen. The PREN calculator on this site uses midpoints for exactly the opposite reason: there, crediting unguaranteed content would overstate corrosion resistance. Each calculator states which figure it used, per element.
What is the difference between method A and method B?
Both live in EN 1011-2 Annex C. Method A works from CEV and a set of charts and hydrogen scales; method B is the closed-form expression implemented here, built around CET. They are different fits with different validity windows and they do not have to agree — where they differ, the governing document is whichever your specification names. This page implements method B only, and says so above the form.
Is this the preheat or the interpass temperature?
It is the MINIMUM preheat temperature: the temperature the joint must have reached before the arc is struck. In multi-run welding the same value is normally held as the minimum interpass temperature, so the joint never drops below it between runs. The maximum interpass temperature is a separate limit that comes from the base metal and the WPS — this formula does not produce one.
Why does entering a stainless grade produce a refusal?
Because the CET expression behind method B was fitted on non-alloyed and low-alloy steels, and its own window caps chromium at 1.5 %. A stainless grade carries ten times that, so the refusal names chromium and stops there. That is the correct outcome, not a gap: austenitic stainless steels are not hardenable in the martensitic sense this method is about, and preheat for them is governed by entirely different considerations.