16.12.2005
In spring 2005, a CIPM Key Comparison for high-pressure natural gas was successfully completed. It turned out that only three of all high-pressure test facilities in the world were prepared and technically in a position to participate. The result of this CIPM comparison is that the reference value is identical with the harmonized European natural gas cubic metre which has been made available by PTB, NMI-VSL and LNE since May 2004.
On May 04, 2004, the national metrology institutes of Germany, the Netherlands and France (PTB, LNE und NMi-VSL) agreed in a contract to realize a uniform gas cubic metre for natural gas under high pressures which is referred to as harmonized European gas cubic metre. In this harmonization procedure, a weighted mean value is formed from three independent and different realizations of the participating partners. This gas cubic metre is realized by the three NMI at the high-pressure test facilities pigsar, Bergum and LADG. It furnishes a stable result and has a smaller uncertainty than the individual single realizations in the participating institutions.
The procedure of the weighted mean value formation was initiated in 1999 between PTB and NMi-VSL and completed in 2004 with the inclusion of the LNE in France. This weighting is not, however, taken as a fixed constant for all times: A German-Dutch-French expert team monitors and controls the quality and reliability of the measurements on both sides of the frontiers and can, by unanimous decision, also change the weightings defined in an annex to the contract.
Another metrologically independent realization of a natural gas cubic metre by a national institute does not exist - neither in Europe nor in Asia or the USA.
Within the scope of the international activities of CIPM/BIPM for the mutual recognition of calibration certificates, key comparisons were organized in all important metrological fields, among other things also in the high-pressure range of natural gas. In April 2005, a comparison for high-pressure gas was completed and the so-called Key Comparison Reference Value (KCRV) defined. It is regarded as the best realization of the respective measurand worldwide. It has turned out that the European harmonized gas cubic metre is identical with this reference value.
The reason for this was that besides the European partners PTB, NMi-VSL and LNE nobody else was ready or in a position to participate in such an international comparison measurement. The pilot laboratory (PTB) invited the operators of state-owned and private high-pressure test facilities to participate, but after negotiations of almost 5 years, all except for the above-mentioned European partners rejected the invitation.
Approximately one year ago, Canada joined the harmonized European gas cubic metre via the CNRC and implemented it on its national natural gas calibration standard TCC. China (AQSIQ) is carrying on negotiations with PTB to adopt the KCRV for its new WEPP test facility. In the meantime, this realization of the gas cubic metre is disseminated also to Eastern Europe and Asian countries. Western Europe has already largely been linked-up.
In view of the natural gas consumption in Europe of approximately 400 billion cubic metres a year, it is a great advantage above all for the natural gas associations to be able to compensate their gas balance in an even better way. This also allows a better service to be rendered to the end-consumer. The European harmonized reference value now commonly valid guarantees the gas associations as well as the end-consumer that the same is measured on both sides of the frontiers.
Public gas trade is a gigantic market. In Germany alone, 100 billion cubic metres of natural gas flow per annum through the pipeline systems to the end-consumers: this corresponds to a monetary value of approximately 20 billion euros. However, this natural gas measurement is not easy. The best test facilities which measure flowrates on high-pressure natural gas pipes achieve - under optimal test conditions - a measurement uncertainty of approximately 0.15 %. In view of this currently achievable accuracy it is all the more important not to have to accept an additional measurement uncertainty during the crossing of a frontier.
Contact person:
D. Dopheide, Department 1.4, email: Dietrich.Dopheide@ptb.de