Preheat Temperature Calculator

Inputs

Thickness *

Use plate thickness or effective joint thickness.

Ambient temperature (degC)

Cold conditions may raise the minimum preheat.

Heat input (kJ/mm) *

Typical range: 0.5 to 2.5 kJ/mm.

Welding process

Used only as a minor adjustment.

Hydrogen level

Higher hydrogen generally increases preheat demand.

Restraint level

Higher restraint can increase cracking risk.

If you do not have full chemistry, enter what you know and keep the rest at zero.

C

Mn

Cr

Mo

V

Ni

Cu

Reset

1) Carbon equivalent (IIW):

CE = C + (Mn/6) + (Cr + Mo + V)/5 + (Ni + Cu)/15

2) Preheat estimate (guidance model):

T_target(degC) = 50 + 400*max(0, CE - 0.30) + 0.50*t(mm) + adjustments

Adjustments include hydrogen, restraint, process, ambient, and heat input effects.
Output is bounded to typical planning ranges (50C to 350C).
Use project requirements, WPS, and governing codes for final decisions.

Thickness (mm)	Ambient (C)	Heat input (kJ/mm)	C	Mn	Cr	Mo	Ni	Cu	Hydrogen	Restraint	CE	Target preheat (C)
20	15	1.2	0.18	1.20	0.30	0.10	0.20	0.15	Low	Medium	0.47	~110
35	5	0.8	0.22	1.40	0.55	0.20	0.30	0.20	Medium	High	0.63	~200
12	25	1.6	0.12	0.90	0.10	0.00	0.10	0.05	Low	Low	0.28	~55

Example outputs are illustrative and depend on job conditions.