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The newly established 7000 m³ h-1 gas flow standard at NMI

Within the next year, Australia will become the largest exporter of natural gas in the world, with accurate measurement now underpinning the sale and shipment of billions of dollars of gas. Domestically, higher gas prices are now placing greater importance on accurate and reliable measurement: a ±1% uncertainty can translate into millions of dollars per day in custody transfer both between suppliers and through to consumers.

To respond to this rapidly expanding area, the NMI gas flow team has established a new standard to cover a flow range up to 7000 m³ h-1.  To reach these flows requires a “build-up” from volume-prover references at the 25 m³ h-1 level. This successive build-up usually entails compounding uncertainties, however NMI’s unique abilities in sonic-nozzle manufacture and calibration allows us to do this with minimal increase in uncertainty.  The new facility, nick-named the Blue-Spaghetti-Monster-Array, comprises 28 nozzles with diameters up to 21.2 mm connected in parallel to produce flows from 50 m³ h-1 to 7000 m³ h-1 and achieves an uncertainty below 0.12%.

We needed to face challenges such as understanding the pressure and temperature drops across the throat of these large nozzles to ensure optimum performance at highest possible accuracies and at the same time reducing operational cost. Furthermore, the calibration of these large nozzles required the development of a new method that took advantage of the compressibility of air to calibrate them in series with other nozzles. 

The process of developing these new standards gives NMI unique skills in gas-flow measurement which can be used to assist in solving gas-flow measurement issues. For example, NMI is currently coordinating proficiency testing amongst Australian labs to ensure reliable and robust traceability between them and the rest of the world.

Due to its thermal expansion and compressibility, gas flow measurement requires good familiarity in both pressure and temperature measurements as well as an understanding of the propagation of these effects into measurement uncertainty, for example 1oC corresponds to 0.3% in flowrate. NMI has metrology training courses in these and many other measurement disciplines. We are able to tailor a measurement course to your company’s specific needs and conduct it at your work place. We are currently considering the development of a specialist course in gas-flow and would greatly welcome your feedback on this new proposal. Please This email address is being protected from spambots. You need JavaScript enabled to view it. for more information or to discuss your specific needs.