The calibration of gas meters for flow rate measurements of natural gas at high pressure is of critical importance for gas importers, gas distributors and international trade, especially for Europe, as western Europe imports most of its natural gas consumption from Russia and Norway. The total gas consumption in western Europe is about 400 billion cubic metres per year.

Key comparisons (KCs) have been organized among all national metrology organizations (NMIs) worldwide that maintain national standards and take care of natural gas metrology. It turned out that, for the time being, only three NMIs were ready to participate, as no other NMIs or countries maintain national standards. These three NMIs are PTB in Germany, NMi-VSL in the Netherlands and LNE in Paris.

All existing facilities in the world were invited to participate, but they all refrained from participation, as they are not yet ready, e.g. CEESI, NIST, SwRI and TCC. Russia does not maintain a calibration facility so far. For more details we refer to the full report.

The KCs were conducted in November/December 2004 at flow rates over a wide overlapping range of flow rate and pressure using a set of gas meters in series. The transfer package comprises of a turbine meter and an ultrasonic meter put in parallel. Flow rates between 65 m³ h^-1 and 1000 m³ h^-1 and pressures between 10 bar and 47 bar have been applied.

The final report presents the degree of equivalence among the participants as well as the degree of equivalence to the KCRV and confirms all claimed uncertainties of the national calibration facilities of Germany, the Netherlands and France very well. In addition E_n values have been reported too.

The last chapter of the final report shows that the so-called 'Harmonized European Natural Gas Cubic Metre' is identical with the KCRV of this KC. This ensures that the European facilities disseminate the best available realization of the gas cubic metre at high pressure, namely the KC, to their customers. In this respect the KC5a has a very high economic impact for all customers.

Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.

The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).