Carbon equivalent: CE, CET and Pcm

By Okan Can Kahraman · Updated 2026-10-29

A carbon equivalent turns a steel's chemical analysis into a single number that indicates how hard the heat-affected zone gets and how sensitive it is to hydrogen cracking. Different formulas suit different steels and preheat methods.

The three formulas

CE(IIW) = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
CET     = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40
Pcm     = C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B

Which one to use

• CE(IIW) is the classic value printed on most plate certificates and used in EN 1011-2 Annex C method A and in many product standards (EN 10025 sets maximum CEV values).
• CET is used in EN 1011-2 Annex C method B, which also takes hydrogen and heat input into account. It works well for modern C-Mn, fine-grain and low-alloy steels.
• Pcm (Ito-Bessyo) suits low-carbon steels, roughly C below 0.12 %, such as TMCP and pipeline steels; AWS D1.1 uses it in its guideline on alternative methods for determining preheat.

Example: typical S355J2

With C 0.17, Mn 1.40, Si 0.30, Cr 0.05, Mo 0.02, V 0.01, Ni 0.05, Cu 0.15 %: CE(IIW) ≈ 0.43, CET ≈ 0.32, Pcm ≈ 0.26. A CE around 0.40–0.45 means preheat is needed from moderate thicknesses; see the S355 preheat table.

Practical notes

• Use the analysis from the 3.1 inspection certificate, not the standard's maximum values; the real CE is often much lower.
• Boron strongly raises Pcm (factor 5) even at a few ppm.
• A carbon equivalent alone does not give a preheat; thickness, hydrogen level, heat input and restraint also count.

The preheat temperature calculator calculates all three from your analysis and applies the matching preheat method.