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Key words: crude oil metering, large diameter flowmeter, failure rate, measurement accuracy Large diameter flowmeter is a metering device manufactured by Shanghai Instrument No. 9 Plant in 1973. An oil field supplies crude oil to a petrochemical company's refinery every year. Most of the metering equipment is To measure. The oil fields used to transport crude oil to refineries are three large-caliber screed flowmeters. They work at the same time as the three large caliber flowmeters of the refinery. If the measurement is inaccurate due to equipment failure, both parties will check the other equipment. In most cases, Loss of the equipment will occur if the equipment fails. Therefore it is particularly important to reduce the failure of metering equipment. Three large-diameter flowmeters installed in the crude oil metering plant of a refinery have been operating for more than 30 years. Equipment wear has been severe and failures have occurred. This has seriously affected the measurement accuracy of crude oil and caused huge economic losses to petrochemical companies each year. Since manufacturers stopped producing this type of instrument 10 years ago, it is impossible to obtain the support of manufacturers from the aspect of technology and accessories, which has brought difficulties to our daily maintenance work. In order to ensure the normal operation of production and ensure the accuracy of measurement, the failure rate of the primary transmission system of the flowmeter must be reduced.
1 Current Status Survey 1.1 Current Status Survey 1 (See Table 1)
From Table 1, it can be seen that the failure of the primary transmission system is the main reason that affects the measurement accuracy. 
1.2 Current Status Investigation The second-level transmission system is the main component of the large-diameter flowmeter. It consists of a metering box, upper and lower end caps, an active waist wheel and a driven waist wheel. It directly contacts the medium and is affected by speed, high temperature and other factors. Faults occur frequently. In order to find out the cause of the failure, a follow-up survey was conducted. Table 2 is the collation of the follow-up survey data from April to June. 
From the arrangement chart, it can be seen that poor lubrication is a major factor causing frequent transmission failures.
2 Determination of objectives and feasibility analysis Based on the status quo, we have determined the goal of reducing the transmission failure rate from the current 54.5% to 5% or less. The feasibility analysis is shown in Figure 2. 
3 To analyze, confirm, and verify a total of nine end-of-line factors for poor lubrication problems (see Figure 3), use the importance scoring method to evaluate, and find four main factors, and conduct direct observation at the site for verification, as shown in Table 3. . 
4 Formulation of countermeasures Based on the above main factors, corresponding countermeasures have been formulated (see Table 4). 
5 Implementation 5.1 Implementation One of the compressor oils with viscosity of N46 was originally used in the transmission. The lubrication effect is not satisfactory. For the characteristics of fast transmission speed and high temperature, we have re-selected the 18th precision instrument oil. Table 5 is two types of lubrication. Comparison of oil performance indicators. 
5.2 Implementation of the second transmission oil supply has always been done manually 24h. In order to ensure continuous oil supply, we installed a pair of D50mm×120mm oil injection cups and oil return cups on the transmission case. According to the kinematic viscosity of lubricating oil, after several tests, we chose a filling pipe with a diameter of 2mm to ensure 6 The amount of oil drip/min ensures continuous oil supply, see Figure 4. 
5.3 Implementation of the three continuous oil supply problem has been solved, but there are more than 20 gear shafts on the transmission, distributed on the D120mm disc, and there are many shafts on the outer part, which has the problem of non-uniform oil supply. We have extended the central axis and installed an oil pan on the central axis. Many small holes were drilled in the pan. With the high-speed rotation of the central axis, the lubricant spreads around to achieve the purpose of uniform oil supply. 5. 
6 Effect Inspection After taking measures, we investigated the faults of large-caliber flowmeters from August to October of 2007. See Figure 6. 
Reduce flowmeter failure rate, reduce measurement error
Abstract : The oil field is supplied to petrochemical company refinery for measuring crude oil by large diameter flowmeter. After more than 30 years of operation, the fault occurs continuously. The article discusses the use of safety system engineering methods and technological innovations to reduce the flowmeter from the current status of failure investigations, the goal and feasibility of reducing failure rates, the analysis of the causes of failures, the verification and verification, the measures to control the failure rate and their implementation effects. The failure rate, thus improving the measurement accuracy. After taking measures, the flowmeter's failure rate dropped from 54.5% to 5.4%. According to the survey and statistics from January to June, we plotted the fault arrangement diagram of the primary transmission system. See Figure 1. As can be seen from Table 5, No. 18 precision meter oil has the following advantages over N46 compressor oil: low viscosity, good viscosity-temperature characteristics, good oxidation resistance, and oil-free mechanical impurities. Therefore, we chose the No. 18 precision instrument oil.
Fig.1 Failure arrangement diagram of the primary transmission system
Figure 2 Feasibility Analysis of Decreasing Transmission Failure Rate
Figure 3 causes of poor lubrication
Figure 4 shows the transmission oil supply
Figure 5 shows the installation of oil pan on the center shaft
Figure 6 shows the arrangement of large-caliber flowmeter faults
It can be seen from Fig. 6 that the transmission failure is not the main cause of the failure of the flowmeter. Therefore, this work successfully solved the lubrication problem of the transmission lubrication system and reduced the failure rate of the flowmeter to 4.5%.