Vol.3 No.1 2010

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Research paper : Development of primary standard for hydrocarbon flow and traceability system of measurement in Japan (T. Shimada et al.)−54−Synthesiology - English edition Vol.3 No.1 (2010) used most frequently. Currently, the precision demanded of flowmeters is very strict, and the level of uncertainty required for hydrocarbon flow standard is high.Until now, the standard tested (accepted or rejected) by AIST was used to test many hydrocarbon flowmeters. This standard is a device used by the prefectural inspection agencies to test the small-diameter hydrocarbon flowmeters for commercial use, to prevent disadvantage to the general consumers of Japan, that is, to guarantee fairness. In a system using this standard, the public institute tests a certain function using an appropriate method, and this is expected to greatly reduce the cost of managing the measurement device in society as a whole.On the other hand, with the advance in measurement technology, there has been a recent increase in the demand for highly accurate flow measurement exceeding the range of this system, as well as for measurement of more types of petroleum products and wider flow range, so that the companies can perform voluntary highly accurate quality control on their own. Moreover, with the internationalization of economic and production activities, the international trade of the Japanese petroleum products is increasing, and it is mandatory to guarantee the integrity of the international flow measurement values. Therefore, there is a demand to provide a standard with international integrity to the users and to also offer choices of maintaining the metrological traceability in accordance to the international system. However, there was no calibration facility that could be used as the national primary standard of hydrocarbon flow, and the work of setting up the flow rate using physical quantities such as mass, volume, time, density, temperature, pressure, and others were left to the flowmeter manufacturers and users. Also, since the definition of metrological traceability was scientifically established, the metrological traceability could no longer be maintained with the conventional system that did not address uncertainty.The petroleum tax on the domestic trade of petroleum products is very large at about 6 trillion yen annually[1], and measurement is socially very important. Therefore, the tax office meter (hydrocarbon flowmeter) must have a highly accurate control of instrument error (deviation from standard value) within ± 0.2 %[2]. Currently, several tens of thousands of custody meters are said to be in operation at the petrochemical facilities throughout Japan, as mentioned before, and rationalization is highly in demand since great cost and human resources are needed to maintain precision.3 Technological objective for creating the hydrocarbon flow standardSome people may misunderstand that to measure the hydrocarbon flow or the quantity (volume or mass) of the petroleum products, the flowmeter can be easily calibrated with high accuracy by calibrating the volume tank (volume prover) or the weighing scale (mass comparator) with high accuracy because they are parts of the calibration device. Although the uncertainty of the volume or mass is part of the source of calibration uncertainty, there are several other sources that significantly affect the calibration uncertainty such as: temperature, pressure, and density measurements; leakage of test liquid from the branch of the connecting pipe used in calibration; and the effect of the flow velocity distribution and flow velocity fluctuations in the pipes. In practice, these factors may turn out to be dominant in the overall calibration uncertainty in many cases, and it is necessary to evaluate these uncertainties. In the actual measurements using the flowmeter, there are many cases where the conditions in which the flowmeter was calibrated and the condition in which it is actually used are different. Therefore, it is necessary to evaluate the effects of the pipe formation, temperature, pressure, properties of the test liquid, and others on the flowmeter characteristic, and to estimate the measurement uncertainty in the actual measurement condition. Since it is impossible to conduct these evaluations for all measurement conditions due to cost and time restraints, it is necessary to pinpoint the source of uncertainty according to the requirements and to estimate the uncertainty efficiently.In petroleum products, liquid expansion of about 0.1 % is seen every 1 ºC. However, in the petroleum products trade, the measured volume is used as is without necessary corrections according to the temperature of the measurement environment. On the other hand, the petroleum products, which are energy resources, technically should be traded by mass, and it is necessary to supply the flow standard as mass flow in addition to volume flow for the new national flow standard.4 Investigation of method for the provision of hydrocarbon flow standard 4.1 Provision of hydrocarbon flow standardIn the actual on-site measurement of the hydrocarbon flow, it is necessary to conduct the flow measurements with minimum uncertainty using minimum resources (cost, time, etc.), and the reliability must be guaranteed. Since the flow standard is set up using other physical quantities such as mass, volume, time, density, temperature, and pressure, it is necessary to clarify “who and where” the set up of the standard flow from other standards will be done in providing the national standard. Since there was no calibration device for hydrocarbon flow that could be used as a national standard in Japan, the work of setting up the flow rate from other physical quantities was left to the flowmeter manufacturers and users, and the reliability was unknown. The provision of the flow standard can be categorized roughly into the following three:

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