Steel and preheat
Carbon equivalent CE (IIW)
- where
- carbon equivalent (%)
- carbon (%)
- manganese (%)
- chromium (%)
- molybdenum (%)
- vanadium (%)
- nickel (%)
- copper (%)
Explain this equation
Works out the IIW carbon equivalent of a steel from its chemical analysis on the mill certificate. It is a quick guide to how prone the steel is to hydrogen cracking, and is used in the BS EN 1011-2 preheat method A.
Carbon has the biggest effect on how hard the heat-affected zone gets. Each other alloying element also adds hardenability, but less, so it is divided by a factor: manganese counts a sixth as much as carbon, chromium, molybdenum and vanadium a fifth, nickel and copper a fifteenth. The weighted total is expressed as an equivalent amount of carbon.
An empirical weighting worked out from tests on many steels.
Sense check: a typical S355 at 0.18% C and 1.4% Mn comes out around 0.44. Below about 0.40 steels are generally easy to weld; above about 0.45 preheat is often needed.
Watch out: use the actual cast analysis from the certificate where you have it. The maximum values in the standard give a pessimistic result.
Turns a steel’s chemical analysis (from the mill certificate) into one number for hardenability and hydrogen cracking risk. It is the CE used in BS EN 1011-2 method A and the CEV limit in BS EN 10025 steel grades.
Enter your values to see the result.
Good to know
Take the cast analysis from the inspection certificate (3.1 cert). The higher the CE, the harder the heat-affected zone and the more likely preheat is needed. Use CE with the combined thickness, hydrogen scale and arc energy in the BS EN 1011-2 method A charts to read off a preheat.
Common mistake
Using the grade’s maximum CEV from the product standard when the actual cert is available. The actual value is usually lower and may save preheat.
Limits
CE(IIW) suits carbon–manganese and low-alloy steels; TWI notes it is less suitable for very low-carbon modern steels, where Pcm or CET is preferred. Enter blank elements as zero.
Sources
- TWI FAQ: What is the difference between the various carbon equivalent formulae used in relation to hydrogen cracking? (CE(IIW), Pcm, CET in EN 1011-2)
- BS EN 1011-2:2001 Welding – Recommendations for welding of metallic materials – Part 2: Arc welding of ferritic steels (Annex C: CE and CET preheat methods; Annex D: cooling time t8/5)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the welding procedure specification (WPS), BS EN ISO 15614/9606, BS EN 1090, BS EN 1993 and manufacturers’ data. Structural welds need qualified welders and engineered designs.