Analysis and solution of common faults of mass flowmeter

Mass flowmeter based on Coriolis force is a kind of flow measuring instrument with high accuracy, high technology, stable and reliable operation. Now it is widely used in a series of occasions such as single well metering, joint metering and liquefied gas metering in Tuha oilfield, and some faults have been exposed. This paper focuses on analyzing how to deal with the failure and maintenance of mass flowmeter, and use mass flowmeter reasonably and effectively.

1 Introduction

Mass flowmeter is a kind of flow measuring instrument with high precision, high technology, stable operation and reliability. It can directly measure the mass flow of fluid. With the development of social economy and technology, mass flowmeter is more and more widely used in on-site measurement and trade settlement. At present, a large number of Coriolis mass flowmeters have been introduced and applied in various occasions. The use of this flowmeter has greatly promoted the improvement of measurement level, but also exposed many problems.

One of the most important is the lack of reasonable and effective methods and measures to deal with the fault. How to deal with the fault of the flow meter, especially the general technical maintenance personnel do not know where to start and how to eliminate some minor faults, which requires us to carefully analyze the problem, sum up experience, troubleshoot, in order to make the mass flow meter better in the actual production, we should also do a good job of instrument detection and maintenance, to ensure the measurement accuracy of the mass flow meter.

2. Common troubleshooting of mass flowmeter

We have summarized and concluded the problems of mass flowmeter in the verification and use, and found that the fault can be large or small, but can not be ignored, otherwise there will be significant measurement error, now the multiple failure analysis and treatment process is provided to you for reference.

The following will be illustrated with specific examples:

Example 1: A unit uses Coriolis force type mass flowmeter as quantitative control meter in the primary oil transport depot. In the process of sending the car tanker, there are more and less phenomena, but the verification result of the flowmeter is qualified. After careful analysis on the site, it is found that the rapid closing of the solenoid valve located in the downstream of the flowmeter causes a strong fluid hydraulic impact, which has a great impact on the sensor work. If the flowmeter and solenoid valve transposition (that is, let the solenoid valve in the front, the flowmeter in the back,) will cut off the influence of the solenoid valve closed on the flowmeter, so that the working condition of the flowmeter is restored to normal.

Example 2: During the operation of a Coriolis force mass flowmeter in a factory, the measurement value deviates greatly from the measurement of the oil tank. After inspection, it was found that the installation position of the sensor was too close to the pump room. When two pumps were working at the same time, the vibration was too large, which affected the stable operation of the sensor. When the sensor was moved away from the vibration source, the situation returned to normal.

Example 3: A factory uses Coriolis force mass flowmeter to measure liquefied petroleum gas. Its normal density is between (0152~0156) g/cm3, but in the process of measurement, the density display value is often lower than 015g/cm3. At this point, even if no fluid passes through the pipeline, the flow meter may have positive and negative direction virtual flow, and the cumulative value increases or decreases. The main reason for this phenomenon is that the flowmeter is under pressure, liquefied gas liquefaction, medium gas-liquid two-phase ratio exceeds the specified range, so that it is not suitable for the normal use of the flowmeter requirements.

There are generally two solutions. One is to improve the pressure of the process pipeline and the pressure of the flowmeter to avoid vaporization of the process medium. The other is to use the small flow rate and low density excising function, that is, to make the flowmeter not record when the flow rate is lower than the specified one, or to use Coriolis force mass flowmeter with the function of selecting measurement according to the density range of the measured medium. The meter is not measured when the density of the medium is below a certain range.

Example 4: A Coriolis force mass flowmeter in a oil production plant often appears the phenomenon of phantom metering, that is, when there is no flow in the pipeline, the cumulative count of the flowmeter will change. After careful inspection at the site, it was found that the installation support at both ends of the sensor does not meet the requirements. One is that the support at both ends is not equidistant, and the other is that the bottom of the support is suspended from the ground without a firm connection. After measures were taken to make the installation of the support at both ends of the sensor meet the requirements, the metering situation of the flowmeter returned to normal.

3. Test and maintenance of mass flowmeter

3.1 Zero check (zero calibration) Zero drift is a problem often encountered in the actual operation of Coriolis force mass flowmeter: there are many factors causing the zero drift, such as the installation stress of the sensor, the structural asymmetry of the measuring tube, the change of the physical characteristic parameters of the measured flow body, etc. Especially in the small flow measurement, the effect of zero drift on the measurement accuracy is more serious. So it is very necessary to carry out regular zero check and adjustment.

Zero point inspection shall be carried out at least once every three months. If production permits, the time interval of zero point inspection shall be shortened appropriately for Coriolis force mass flowmeters installed at important monitoring points. The completion of zero calibration is the key to directly affect whether the flowmeter runs within the precision range.

3.2 Check of Working parameters During the use of the flowmeter, it is necessary to pay frequent attention to whether the set working parameters have changed and whether the displayed flow, density and temperature values are normal. If there is a large discrepancy with the actual value, zero flow calibration can be carried out again according to the method described in the operation manual. If you still feel abnormal after completing the above work, you should check whether the working parameters set inside the transmitter are correct.

3.3 Observe the fault indication of the flowmeter regularly According to the different models, specifications and manufacturers of the flowmeter, the fault display mode and content are different. For different fault alarm instructions, you can check the product instruction manual to determine the cause of the fault and deal with it.

3.4 Regular and comprehensive inspection and maintenance For the flowmeter in use, it should be regularly and comprehensively inspected: from the appearance of the sensor, the firmness of installation, the vibration of the process pipeline, the indication of the transmitter and the display instrument and other aspects, the problems should be dealt with in time.

3.5 Establishment of flowmeter files In order to ensure the long-term and reliable operation of the flowmeter, users should establish flowmeter files, record each inspection, maintenance and verification in detail and load them into the files, so as to facilitate better maintenance and use in the future.

3.6 Maintenance flowmeter for the measurement of fluid prone to scale formation (such as scale formation and wax formation), the operation of the device should be checked frequently. When the flowmeter is found to work abnormally or deviate greatly, the possibility of scale formation in the sensor should be considered first, and the sensor should be removed and treated with appropriate methods such as purge or cleaning.

3.7 Periodic calibration According to the different application occasions of the flowmeter, and according to the requirements of the standard system.

conclusion

To sum up, correct installation, reasonable process pipeline configuration and good application environment conditions are very important for the normal use of mass flowmeter. The daily detection and maintenance of mass flowmeter can not be ignored. Only in this way can we give full play to the advantages of high accuracy, strong stability and reliability in actual production.