Coriolis flow meters are one of the most popular flow measurement technologies in the world today for high-accuracy measurement of single-phase liquids, gases, and even slurries. They are capable of measuring both mass and density directly and can also infer the volume flow. They can be installed in challenging process environments and have been successfully deployed with non-Newtonian fluids, high-viscosity fluids, pulsating flows, and even at extreme temperatures and pressures.
However, it is known that operating most Coriolis flow meters at a pressure that differs from the original calibration pressure requires compensation else significant measurement errors will occur. Pressure impacts and coefficients appear to vary by manufacturer, meter geometry, and sensor material. Furthermore, the manufacturer’s published pressure compensation coefficients are not fully traceable. To date, there has not been sufficient research exploring the consistency of the pressure compensation for identical Coriolis flow meters.
This paper presents the findings of research conducted at the TÜV SÜD National Engineering Laboratory (NEL) Elevated Pressure and Temperature (EPAT) oil flow facility to investigate the pressure effect uniformity for matching Coriolis devices. The first stage of the experimental program calibrated three identical DN80 Coriolis flow meters at a range of pressures with no pressure compensation applied. A pressure compensation coefficient was then derived from the data and the Coriolis meters were then calibrated at two alternative pressures to ascertain the robustness of the coefficients and whether the compensation could be extrapolated successfully.
From the experimental results, it can be concluded that the pressure effect for the three DN80 Coriolis flow meters was extremely repeatable and consistent with a discrepancy of less than 0.025% between the devices at 80 bar. Whilst the mass flow was significantly affected by fluid pressure, the fluid density did not appear to be influenced. The pressure-corrected results were also well within the manufacturer’s specification of ±0.1%.
This paper details the findings of an experimental program researching the pressure effects of three identical DN80 Coriolis flow meters. The research was completed using the Elevated Pressure and Temperature (EPAT) oil flow facility which is located at the TÜV SÜD National Engineering Laboratory (NEL) in Glasgow.
Coriolis flow meters can be utilized for nearly all flow applications, with a growing market share in many different
industries such as oil & gas, food & beverage, chemicals, and pharmaceuticals amongst others. One of the key advantages of Coriolis flow meters is that they provide a direct measurement of mass flowrate and product density with stated uncertainties as low as ±0.05% for mass and ±0.2kg/m3 for density respectively [, , ]. The exact specification differs by manufacturer and model type. In industry, mass flow measurement is often preferred to volume flow due to mass being independent of the process conditions such as pressure and temperature. Therefore, no compensation coefficient factors need to be applied – and a possible source of error is eliminated.
Although Coriolis flow meters provide a direct mass measurement, it is recognized that Coriolis flow meters can be affected by process conditions. Fluid temperature, pressure impacts and viscosity variations, and ambient temperature are known to influence the measurement performance of Coriolis flow meters [, , , , , , , , ]. Whilst these parameters are of concern, this research program focussed exclusively on the effects of pressure on Coriolis flow meter performance.
The findings of this experimental program provide independent research data relating to pressure effects on Coriolis flow meters with a view to better informing end users and providing the information needed for the revision of flow standards. This work contributes to the Department for Business, Energy & Industrial Strategy (BEIS) Flow Programme project, ‘Determination of the Pressure-Effect on Coriolis Flow Meters’. The value for industry and society will be improved pressure compensation coefficients for Coriolis flow meters, enabling more accurate flow metering and therefore ensuring more accurate fiscal metering for UK tax revenues, and process optimization for operators.
Coriolis flow meters
The measuring principle for Coriolis flow meters is based on the controlled generation of Coriolis forces. These forces are present when both translational and rotational movements occur simultaneously. The amplitude of the Coriolis force depends on the moving mass, its velocity in the system, and thus on the mass flow. Instead of a constant angular velocity, Coriolis flow sensors use oscillation
The historical view presented by manufacturers was that Coriolis flow meters should be independent of temperature, pressure, viscosity, conductivity, and flow profile. However, many manufacturers now state that their devices are affected by fluid temperature, pressure, and Reynolds Number. Research by Mills has shown this to be the case [, , ,15]. Indeed, some vendors have compensation coefficients for Reynolds Number and pressure impacts included in their software and all have temperature.
NEL elevated pressure & temperature facility
The EPAT flow facility, located at NEL in East Kilbride Scotland, consists of a high (150mm) capacity and a low (80mm) capacity flow line. These can accommodate nominal pipe sizes from 12mm to 250mm and up to 10m of horizontal straight lengths. The facility can operate at line pressures from 4barg to 93barg and temperatures from 20°C–80°C. The test fluid can be delivered at flow rates up to 300t/h. Table 2 details the specifications of the EPAT Flow Facility. Fig. 3 shows a SolidWorks
The results for the three DN80 Coriolis meters have been analyzed individually and subsequently compared for pressure effects, zero effects, repeatability, and reproducibility. The process value ‘drive gain’ from the Coriolis flow meters has also been included in the analysis. The following sections will discuss the general trends and performance for pressure effects and zero effects at pressure impacts. The last section of the results will compare the results for the 3m with respect to the pressure.
Three identical, commercially available DN80 Coriolis flow meters have been calibrated across a range of pressures to investigate the consistency of pressure effects. The mass flow and density output of the devices were recorded along with additional diagnostic values via the Coriolis software. The repeatability and reproducibility of the Coriolis meter’s mass flow performance were also evaluated with respect to pressure.
The pressure effect has been shown to be tremendously consistent between the meters
Overall the findings described in this paper reinforce the significance of pressure effects on Coriolis flow meters. In summary:
- The mass flow performance of the DN80 Coriolis flow meter was significantly affected by the fluid pressure. The density performance did not appear to be affected by the fluid pressure.…
- The mass flow pressure effects for Coriolis meters were extremely robust and consistent between devices. The repeatability and reproducibility of the devices were excellent and did not
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
The work was funded by the Department for Business, Energy & Industrial Strategy (BEIS) Flow Programme. I couldn’t find this on the list of funders.