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Towards the global natural gas cubic meter

After the cubic meter for natural gas under high pressures was unified by the national German, French and Dutch metrology institutes (PTB, LNE and NMi-VSL) last year, international Key Comparisons for high-pressure gas have been completed in April 2005. Participants, for the time being, were limited to these European institutes, and a Key Comparison Reference Value (KCRV) has been determined.

The natural gas cubic meter was uniformly realized on the European test facilities pigsar, Bergum and LADG.

Public gas economy is a gigantic market. In Germany alone, approximately 100 billion cubic meters of natural gas flow each year through the pipeline systems to the end customer. As this corresponds to a monetary value of approximately 20 billion euros, customers and suppliers are interested in precise measurements. Under optimal conditions, the best test facilities for flowrate measurements on high-pressure natural gas pipes, however, merely achieve a measurement uncertainty in the order of 0.15%. However, in the past additional contributions to the measurement uncertainty could occur as well because Germany, the Netherlands and France had realized completely different concepts for natural gas measurements. Thus unfavourable effects on gas trade were possible.

By May 4, 2004 a uniform cubic meter for natural gas under high pressures, referred to as the “harmonized European natural gas cubic meter”, had been realized by the German, Dutch and French metrology institutes (PTB, LNE and NMi-VSL). In this procedure – regulated by contract –, a weighted mean value was created out of the three independent realizations of the partners involved. No other metrologically independent realizations has been established in Europe by other countries. A stable and reliable European standard has thus been created which is affected by a lower overall uncertainty than the individual realizations in the participating institutions. It represents a benefit for fair trade in the gas supply economy.

To extend the recognition of calibration certificates outside Europe, key comparisons are organized within the scope of the international activities of CIPM/BIPM in all important metrological fields. In the natural gas sector, operators of governmental and private high-pressure test facilities from all over the world were invited to participate. As calibration test facilities for high-pressure natural gas operated by metrology institutes are evidently not available outside Europe, only the European metrology institutes PTB, LNE and NMi-VSL participated in the international comparison measurement under supervision of CIPM/BIPM. The KCRV determined in the comparison is identical with the natural gas cubic meter determined in Europe. On this basis PTB supports the establishment of corresponding national standards in different countries including non-European ones to complete global harmonization.