Oil, gas & renewables
modified for use in different fluid mediums. Coriolis flow meters are calibrated at the factory with water to ascertain performance and to derive the meter coefficients. These Coriolis meters are then used for flow measurement in a variety of different fluids such oil, food, pharmaceutics products and even hydrogen, amongst many others. Whilst, Coriolis and flow meters can be calibrated in water and then used to measure another fluid, that does not mean it is the recommended practice for all applications. It ultimately depends on the measurement uncertainty required and the measurement regulations. The ISO 10790:2015 standard provides guidance on the selection, installation, and use of Coriolis flowmeters. However, it includes little practical guidance for their operation at elevated pressures, temperatures, and viscosities. Ideally, the calibration should be completed using the same fluid and pipe work configuration within which the meter will normally operate. In reality this is
seldom possible. Whilst a calibration laboratory will try and match process conditions as much as possible some degree of disturbance to the meter is inevitable. For high value products such as oil, it is vital that the device is calibrated close to service conditions. The regulations stipulate that this must be completed. However, for certain applications, such as the process measurement of a low value product with a low viscosity (~1 cP), operating at ambient temperature and pressure in a pharmaceutical plant, with a large permissible measurement uncertainty, it is entirely feasible that a water calibration would be sufficient. This is partly due to the excellent performance of newer Coriolis flow meters, the process conditions, and the target measurement uncertainty. However, it is still recommended to routinely calibrate the device to determine the meter drift over time. Whatever the calibration philosophy, it is always good practice to keep calibration graphs and control charts of the meter performance as this
will assist in determining calibration intervals and demonstrate meter performance over time. These can then be used to influence future calibration decisions which could help save time, money and make maintenance a much simpler process.
With enough traceable calibration data in multiple fluids and conditions, it might even be possible to determine whether your flow meters can be calibrated in one fluid and then successfully operated in another. As always, if in doubt about the calibration requirements for your flow meter, consult the manufacturer or an independent expert.
TÜV SÜD National Engineering Laboratory
www.tuvsud.com/en-gb/nel
Instrumentation Monthly March 2023
55
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