Check points during flow calibration
At the flow calibration laboratory there are some important issues to be addressed. I have listed them
below in a chronological sequence.
Before calibration start
Agree on the calibration procedure and acceptance requirements. Supplier, client and laboratory personnel should meet to go through the procedure with respect to flow range, number of repeats, verification points and other project specific requirement.
Inspect the flow meter installation. Check that the flow conditioner and upstream pipe is installed
correctly with respect to flow direction and orientation. It is a good practice to take pictures, if allowed, to document the physical installation arrangement.
Check that the same output signal is used during calibration as will be used in the final installation
for traceability purpose.
It is recommended to use pulse output since this is a simple and straight forward representation of the flow rate.
Check the parameter setup of the flow meter to be calibrated.
o Check that the nominal K‐factor (pulses/m3) in the flow meter is used by the flow laboratory.
o Check that inner diameter, path lengths and transducer parameters are entered in accordance with supplier certificates.
o Check that correct linear thermal expansion coefficient and modulus of elasticity (Young’s modulus) is entered into the flow meter for correct temperature and pressure diameter compensation. Typical values for linear thermal expansion coefficient are 1.10E‐05 m/m/C for carbon steel , 1.60 E‐05 m/m/C for SS316 grade steel and 1.30E‐05 m/m/C for duplex material. Typical value for modulus of elasticity is 2.0E+06 bar for carbon and stainless steel.
o Check that the process pressure and temperature is entered manually into the flow meter
for correct diameter compensation.
o Print the parameter setup report to document the flow meter configuration during flow
Check that the process conditions such as pressure, temperature and flow rate are stable during
the flow calibration. Drifting process conditions will most likely affect the flow measurement
Check that there are no alarms generated in the flow meter by its internal diagnostics system.
Check for normal values of automatic gain, percentage of accepted ultrasonic pulses, path
velocities and velocity of sound (VOS) on each transducer pair. The spread in VOS should exceed
0.5 m/s between all transducer pairs during normal flow.
Check the repeatability and linearity towards the calibration procedure.
If the flow correction shall be entered into the flow meter, check that correct parameters are
entered. The correction is entered either as flow weighted mean average, a polynomial or as a
flow rate/correction factor matrix with interpolated correction.
A verification point may be repeated after entering the flow meter correction in order to document correct entering of the flow correction.