CE (IIW) – Carbon Equivalent Calculator
In addition to carbon, other alloying elements also favour cold cracking. Carbon equivalents are often determined to estimate the susceptibility to cracking. There are numerous formulae for describing the carbon equivalent, in which the individual alloying elements are weighted differently.
CEIIW Carbon Equivalent
Avoidance of hydrogen cracking (also known as cold cracking). The formula based on the International Institute of Welding (IIW). This carbon equivalent CEIIW (also called CEV) is included in various standards and codes for pressurised containers e.g. as method A of ISO/TR 17671-2 and method A of the harmonised standard EN 1011-2 Annex C par. 2.2.
Applicable steels: C-Mn steels, fine grain steels and low alloy steels.
Carbon equivalent calculation is performed according to the formula below:
CEIIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) /15 [wt%]
Limit values for applying the formula
CEIIW = 0,30 to 0,70 %wt;
Chemical composition limits for the main alloying elements [wt%]:
C = 0,05 to 0,25; Si = max. 0,8; Mn = max. 1,7; Cr = max.0,9; Cu = max. 1,0; Ni = max. 2,5; Mo = max. 0,75; V = max. 0,20.
The relative sensitivity of steels to forming coldcracking microstructures is called hardenability and can be measured in a number of ways. Perhaps the most popular method of assessing this is by the carbon equivalent (CE) formula, which attempts to equate the relative hardening contributions of a steel’s constituent elements (for example, manganese, vanadium) to an equivalent amount of carbon, which is the most significant hardening agent. The most popular formula is the International Institute of Welding (IIW) equation presented in S31.2, which has been found suitable for predicting hardenability in a wide range of commonly used carbon-manganese and low alloy steels.
It should be noted, however, that for the current generation of low carbon (<0.10 %) low alloy steels that derive strength from a combination of microalloys and thermal processing methods (™ steels) the use of other formulae may more accurately assess hardenability and cold cracking sensitivity
Standards and pressure equipment codes
Standards and pressure vessel codes where this carbon equivalent CEIIW is used:
- EN 13445-4 clause 8.9: recommendation for pre-heating (also for EN 13480)
- Many material standards (EN…, ASTM…) contain maximum CEIIW limit values for certain steels suitable for welding or provide for an optional ordering option.
- ASME BPVC Sect. VIII par. UCS-56-1: recommendation for pre-heating for partial materials;
- ASME BPVC Sect. IX table QW-290.4: WPS essential variables for temper bead procedure qualification
- ASTM SA-20: Supplementary requirement S20 for specifying max. CE with above formula (based on heat analysis)
- ASTM SA-…any material specification for Hydrofluoric Acid Alkylation Service
- API Specification 5L clause 9.2.4 and 9.2.5: max. values only PSL 2 pipe with carbon content C > 0,12 %;
- IGC Doc 120/14 clause D8: CEIIW limit is max. 0,43% for syngas pipelines with carbon content C > 0,12 %;
- IGC Doc 121/04 clause D8: CEIIW limit is max. 0,43% for hydrogen pipelines with carbon content C > 0,12 %;
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