What options do we have for ISO 6578 LNG density calculations from composition?
QuantityWare BCG supports the ISO 6578 (Version 1991, 2017 and 2025) density calculations for LNG. As described in Note 000076, the main difference between these versions is the definition of configuration data, i.e. the k1 and k2 factors and orthobaric molar volumes. Customers may wish to utilize their own, contractually defined, calculation data sets.
NOTE: This is a critical task for any LNG implementation, thus a certified BCG consultant is required to support this task.
You have three options to define the density calculations:
- Utilize ISO 6578:1991 data – Orthobaric molar volumes and k1 and k2 factors:
- Utilize ISO 6578:2017/2025 data – Orthobaric molar volumes and k1 and k2 factors*:
- Use customer specific own data – customizing data: For this option, you need to maintain your orthobaric molar volumes and k1, k2 data in customizing for your LNG MQCI conversion group (as e.g. delivered for template conversion group QUC0):
In addition, rounding settings for the ISO 6578 density calculation model, the revised Klosek McKinley model – as described in Note 000064 – are critical.
Read the ISO 6578 news item for additional information.
* ISO 6578:2025 data is listed with identical values as informative in a different annex compared to the 2017 version.
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