Carbon equivalents are used as a parameter for estimating weldability with regard to crack sensitivity, particularly in the heat affected zone. There are several formulae for describing the carbon equivalent, in which the individual alloy elements are weighted differently.
The carbon equivalent Pcm (also called CEPcm) is based on Japanese results from Ito and Bessyo in 1969. Pcm is designed for newer microalloyed steels with low carbon contents. For steels with low carbon contents or carbon equivalents Pcm ≤ 0.12% has been found be to a better indicator of crack susceptibility. The effect of carbon becomes critical to an HAZ containing large amounts of martensite. Thus, Pcm is a good indicator of hydrogen-assisted cracking in the HAZ because carbon is a heavily weighted factor.
Carbon equivalent calculation is performed according to the formula below:
This Pcm carbon equivalent value is included in some material specifications. These materials contained therein contain Pcm max. values (partly thickness-dependent) in order to categorise them as suitable for certain applications, e.g. hydrogen services.
Carbon content C ≤ 0,12 %
Applicable steels: C-Mn steels, fine grain steels and micro-alloy steels.
Standards and pressure vessel codes where this carbon equivalent Pcm is used:
