Why this matters
Carbon equivalent (CE or CEV) is a single number that compresses a steel chemistry into a weldability index. For procurement engineers, it is one of the simplest tools to compare two heats of nominally the same grade and predict which one will give the welding contractor a hard time on site.
Most specification disputes around carbon steel pipe and fittings (A106, A234, A105, API 5L) trace back to either chemistry tolerances or carbon equivalent. This article explains the formula, its limits, and how to use it in your purchase orders.
Key technical facts
The most widely used carbon equivalent formula is the one published by the International Institute of Welding (IIW), recognised in ASTM, EN and API documents:
CEV (IIW) = %C + %Mn / 6 + (%Cr + %Mo + %V) / 5 + (%Ni + %Cu) / 15
The formula is generally applied to carbon and carbon-manganese steels with carbon content above approximately 0.18%. Below that, formulas such as Pcm (Ito-Bessyo) are more representative for hydrogen cracking risk.
A few reference points:
| CEV value | Typical interpretation |
|---|---|
| Below 0.40 |
