Vol.3 No.1 2010

58/110

Research paper : Development of primary standard for hydrocarbon flow and traceability system of measurement in Japan (T. Shimada et al.)−55−Synthesiology - English edition Vol.3 No.1 (2010) (1) Method where the NMI provides the flow standardIf the national metrology institute (NMI) sets up the flow standard as a national standard, it will be highly reliable, and an ideal traceability system could be constructed. However, there is a diversity of petroleum products and the range of flow rate is extremely wide, and it is not realistic to create and provide the flow standards for all liquid types and flow ranges used in society. Even if all flow standards with small uncertainties at a national standard level can be provided to fulfill the diverse flow measurement conditions actually used, such systems will be extremely expensive. As a result, the user who pursues a balance of uncertainty and cost will most likely select the service of the calibration laboratory described in (2).(2) Method where the calibration lab calibrates the flowmeter using the standards for other physical quantities (such as volume)This is a method where the calibration laboratory conducts the calibration of flowmeters using not the national flow standard, but instead, for example, the mass and density standards. In this method, even in a case where the calibration lab uses the mass and density standards, if the calibration of the flowmeter is done using inappropriate combinations, it may lead to problems such as missing an important correction value or underestimating the uncertainty. Also, establishing the technology to achieve small uncertainty is a great burden on individual calibration labs, and it may result in increased social cost of measurement control. It is also difficult to guarantee reliability, and this may be a disadvantage to the users. On the other hand, this method is highly expandable, and the calibration lab can adapt this method to diverse liquid types and flow rates.(3) Method of using the flow standard provided by overseas institutesAlthough the flow standard is employed in many countries, this method will force dependence on foreign standards, and it is difficult to achieve small uncertainty required in Japan. Also, the flowmeter must be transported abroad for calibration, and the reliability decreases in that process.Figure 1 shows the outline of the representative standard service systems for hydrocarbon flow. In Europe, basically method (1) is employed, and in ranges where the flow standard is not supplied, the approved institution verifies the adequacy of the set-up of flow rates using method (2). To guarantee the performance capacity of the calibration lab, the international standard (ISO17025) requires a skill test, but in several cases this is not conducted appropriately and this is becoming a problem. Therefore, the expansion of the provided range of flow standards is in progress, such as constructing the calibration facility at the level of the national standard for hydrocarbon high-flow (maximum flow of 5000 m3/h).In the United States, method (2) is mainly employed, and the calibration labs set up the flow rates according to the principle of market mechanism. The accreditation of the calibration lab is done by the accreditation authorities. However, there are some labs that are accredited for technologically inadequate uncertainty, where they claim uncertainty much smaller than the national standard with the least uncertainty in the world. To address this issue, the United States has a law to collect a certain ratio of the sales of petroleum products for the American Petroleum Institute (API), and this fund is used to establish and enforce the technical standard (API standard) for guaranteeing the reliability of flowmeter calibration. There is effort for maintaining the reliability of the standard at a civilian level, without depending on the government agencies, but aiming for a small government. For Japan that does not have such a system, it is probably difficult to introduce method (2) directly.Since there was no national standard for hydrocarbon flow in Japan until now, method (2) was employed using a standard established by the law for the calibration and testing of specific measurement devices for trade. However, it became necessary to establish a national flow standard due to the recent increasing Fig. 1 Outline of the hydrocarbon flow standard system.EuropeNational standardsMass standard, volume standard, etc.Flow standardCalibration labsFlow rateFlow rateOn-site flowmetersStrengthen flow standardSet-up forflow rate (2)U.S.A.National standardsMass standard, volume standard, etc.Flow standardCalibration labsFlow rateOn-site flowmeters:Almost noneSet-up for flow rate (2)JapanNational standardsMass standard, etc.Flow standardCalibration labsOn-site flowmetersExpand liquid typesby flow rate(To gasoline, heavy oil)Extend flow rangeby flow rate(To high flow)Kerosene, light oil ~300 m3/hProvision of flow standard (1)Flowrate:Range without national standardProvision of flow standard (1)FlowrateFlowrateProvision offlow standard (1)

※このページを正しく表示するにはFlashPlayer9以上が必要です