ISO 6578 “Refrigerated hydrocarbon liquids — Static measurement — Calculation procedure” has been released as a new version in October 2025 with the designation ISO 6578:2025.
This third edition cancels and replaces the second edition (ISO 6578:2017), which has been technically revised.
- As stated in the new version, the main changes are the alignment with ISO 6976:2016 physical property data and that calculation examples have been moved from the main body into an Annex.
- In addition, calculation data in various Annexes are now designated as “informative” and not as “normative” any longer. This apparently reflects the current global business practise of signing medium and long term LNG delivery contracts which contain various sets of calculation data for the revised Klosek-McKinley equation. Since QuantityWare BCG allows the definition of customer specific data sets for ISO 6578 LNG or LPG density calculations, QuantityWare BCG implementations for LNG are compliant with ISO 6578:2025.
- For LPG, the alternative density calculation models (Francis equation and COSTALD routine) are both not referenced (as informative) any longer. The simplified density calculation formula is provided with molar volume data (at 15 °C, only) as informative data. This density calculation formula may be combined – for LPG with less than 20 % unsaturated hydrocarbons – with the ISO 91:2017 LPG volume correction factor standards (i.e. GPA 8217 / API MPMS Chapter 11.2.4).
- For LPG with more than 20 % unsaturated hydrocarbons, no guidance is apparently available (as both the Francis equation and COSTALD routine are no longer referenced).
