A prover is a device that is used to check the flow meter and we can use this to check the liquid or the gas flowmeter and a prover can be used to calibrate the flow meter. We can test a flowmeter by using a prover, the meter proving is done to determine the accuracy of the flow meter. The proving principle is the same for all the flow meters. By doing the meter proving we can ensure that the flow measurement will be accurate. By doing the meter proving we can determine certain factors like K factor, accuracy, linearity over the flow range, and also we can determine the repeatability of the flow meter. We can determine the deviation of the flow meter by doing the proving, the deviation magnitude is the factor meter. The factor meter can be used to determine the amount of flow that occurs and it will be measured by the measuring equipment. So by doing the meter proving we can determine how the meter performs and how it deviates and according to this, we can adjust the measured quantities for the inaccuracies. The inaccuracies can happen in a flow meter because of the installation and also due to the operations.
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Why proving should be done to flow meter?
The proving must be done to a flow meter because the operating conditions would vary from the conditions under which the meter is calibrated. The performance of a flow meter would vary in the field because of the installation effect from the piping, mechanical wear of the meter, and it could also happen because of the changes in the physical property of the measured fluid. So a flow meter must be proved to adjust to these changes. Most flow meters are proved on a periodic basis, certain meters are proved for each batch transaction. The meter proving can be considered as the calibration of the flow meter, because of the change in the operating conditions the flow meter should be recalibrated. The flow meter proving would provide a good relationship between the meter output and also the fluid flow rate. It would also correct the fluid operating conditions which are varied and they also correct the variation due to the mechanical degradation. The error in the flow meter can also be determined by proving and because of this proving is inevitable in the case of flow meters. By proving a flow meter we check not only the meter but also the entire meter system. A flow meter would cause an error in case if the meter is dirty, in case we install a new meter it could have debris due to the construction and all this can be determined by meter proving.
What are the factors that must be considered while doing the meter proving?
Proving conditions must match the operating conditions
- Flow rate
- Maximum and minimum flow rate
- Characteristics of the liquid API gravity, and viscosity
What are the major requirements for meter proving?
- The meter proving must be done under normal conditions, which means that the flow meter should be proved in the exact condition in which it operates.
- The flow meter prover should have the capability to provide the proving runs for the required duration
- In order to do the proper proving certain number of runs must be made
- The meter prover calibration should be traceable to the calibrated test measures.
What is the difference between meter proving and meter testing?
Meter proving is done to determine the correction factor or the meter factor and by doing this we can vary the measured quantities to achieve accuracy. A flow meter proving is done by comparing the field meter with the prover. So meter proving is done to achieve accurate measurements.
The meter testing is the testing of the flow meter for any damages or faults, like doing a visual inspection of the device for leaks or for installation deficiencies. So a meter testing would mostly check for the faults in the meter, in meter testing there won’t be any comparing of the measured volume to the primary reference device.
How to select a prover?
- Stationary or mobile prover can be selected according to the requirements
- Minimum flow rates
- Pressure and temperature ratings
- It must be selected by considering the maximum allowable pressure drop
- Properties of the fluid
- Minimum flow rates
What are the conditions that must be satisfied before doing the meter proving?
During the meter proving the condition of the process fluid should be really stable and it must be stable throughout the process. So the conditions such as pressure, temperature, density, and flow rate should be stable while doing the meter proving. Before starting the meter proving to allow the liquid to flow through the meter and prover long enough so that the condition should stabilize. We should check if there is any leak in the prover or meter. Before proving we should check if the flow rate is within the meter range, we should also check if the prover is suitable for the flow rate and pressure. Make sure that the prover seals, o rings, proving spheres, etc must be compatible with the product.
Pre proving assessment
- Connect the prover to the meter after ensuring that the prover is suitable for the product
- Make sure that the sealing integrity of the divert valve is good
- Make sure there is no leaks in the block and bleed valves
- Check if all the temperature and pressure device is operational
- Make sure that the divert valve is operational
- Make sure that the products from the previous proving are removed
- Make sure that there is no air or vapor retained in the prover
- Check all the wiring connections
How to do the meter proving?
The meter proving must be done in a way by placing the flow meter in series with the meter prover. This has the known base volume in a way that all the fluid that the flow meter measures would be measured by the meter prover too. The frequency for the proving is depended on the operating conditions and because of this, it is not possible to determine a proper time for all the conditions. The meter proving should be done frequently, the proving frequency can be reduced if the factors are under control.
What are the types of meter proving?
There are different methods in which the flow meters can be calibrated and they are
- Calibration by using other meter and it is mostly called a master meter
- Calibration by using a compact prover
- Calibration by passing a specified mass of fluid through the meter with the help of mass balance
- Calibration by passing a specified volume of liquid through the meter with the help of a volumetric tank
Unidirectional meter prover
In the unidirectional prover, there will be only one-way flow, so the unidirectional fluid flow will be used to calculate the volume, and then it will be compared to the standard volume. The operation of this prover is that the fluid will flow through the line and a sphere will be placed in the flow. So the sphere will pass the detector due to the fluid flow. So when the sphere comes in contact with the first detector then the detector would begin the measurement and when the sphere passes the second detector then the measurement will be stopped. Thus the flow of the fluid and the pipe area can be calculated by this, the fluid volume can be determined by evaluating the total volume that passes from detector1 to detector 2.
This type of meter prover would use the fluid flow in two directions, back and forth in the same prover pipe in order to calculate the volume of the flow, and then it will be compared with the standard volume which has been calibrated. This type of meter prover is widely used for many industrial applications, this is a reliable meter proving technique. In this type of prover, there will be a four-way valve, a flow reversing valve, and this would initiate the return of the bidirectional prover the sphere will be passed through the calibrated section of pipe in both directions. There will be a forward and reverse run meter because the meter proof is in U shape. In order to get stability, the round trip must be continued several times.
Master meter prover
This type of proving method is used where high accuracy is required. The master meter will be connected in series to the flow meter which is to be proved and their readings will be compared. The master meter has been calibrated against a standard. We can use the master meter frequently to check the flow meter in order to determine its accuracy.