The international BIPM/CIPM key comparison reference value for natural gas flow at high pressure and its metrological meaning for natural gas trading

The paper describes the background of the European Harmonized Reference Value for the cubic meter of Natural Gas at high pressure, which is in use in Germany, The Netherlands and France since May 4(th), 2004. The harmonization process began on November 1(st), 1999 between Germany and The Netherlands and has been finalized on May 4, 2004 due to the incorporation of the French LNE to the Harmonized Reference Value. The outcome was named: "Harmonized European Natural Gas Cubic Meter" as realized by three independent National Metrology Institutes. The prerequisites of the harmonization process, underlying procedures, results obtained so far and the mutual benefits will be pointed out as well as the economic consequences for the European market as well as for the international user. The paper shows the degree of equivalence between the three participating NMIs PTB, LNE and NMi-VSL. Under auspices of the BIPM (International Bureau for Weight and Measurers) as well as the CIPM (International Conference for Weight and Measures), which is the highest metrological authority worldwide, so called Key Comparisons (KC) have been conducted to get international reference values for all quantities of interest. Among these KCs, the flow area is of economic importance and Key Comparisons for natural gas flow at high pressure and larger flow rates have been conducted successfully. The outcome of such a KC is the international Key Comparisons Reference Value (KCRV), which is then considered to be the worldwide best available realization of Natural Gas Flow at high pressure. These KCs have been conducted among the National Primary Standards of all nations worldwide, represented by their National Metrology Institutes (NMIs) and have been finalized in December 2004 and the KCRV has been approved by the BIPM in April 2005. It turns out at last that the international recommended reference value is exactly the same as the above mentioned European Harmonized Reference Value.