Flow measurement is arguably one of the most frequent tasks in any industrial environment. Apart from design challenges to ensure a good metering system, there are also installation challenges. No matter how good a design for a given flow metering system is, if the installation is not in accordance with best practices, such a flow meter will not deliver on reliability, performance and accuracy.
In non-fiscal and non-custody transfer applications, flow meters are rarely calibrated and are often left in situ for many years without any thought to their accuracy. In these applications, accuracy is not often the stated goal but maybe repeatability for control purposes but even at that some care and attention still need to be given the flow measurement set up
However in custody transfer applications attention needs to be given to the way and manner the flow meter system is installed. Sadly, in too many instances, the initial installation is often so poorly undertaken, without any regard to basic installation practices. It is therefore highly unlikely that these flow meters will ever meet the manufacturer's stated accuracy. The data
supplied by most manufacturers is based on steady flow conditions and installation in long straight pipes both upstream and downstream of the flow meter to achieve the stated accuracy for the meter.
In practice, most flow meter installations rarely meet these ideal requirements envisaged by the manufacturers. What you find in most meter installations include bends, elbows, valves, T-junctions, pumps and other discontinuities which all produce disturbances that have an adverse effect on meter accuracy.
Best Installation Practice for Flow Meter Installations
To be able to get optimum performance and better accuracy from any flow meter installation, you need to imbibe the following general installation practice:
- Install the flow meter in the recommended position and altitude
- Ensure the meter tube is completely filled with fluid at all times
- In liquid flow measurement installations, ensure there is no air or vapour in the liquid
- In gas flow measurement installations, ensure there are no liquid droplets in the gas.
- Support the piping on both sides of the flow meter to minimize the effect of Vibration.
- Where necessary, provide filtration upstream of the meter to knock out solids from the flow stream.
- In liquid installations, pressure pulsations can be a problem. Therefore, Protect meters from pressure pulsations and flow surges.
- As much as possible, avoid strong electromagnetic fields in the vicinity of the Flow meter.
- Install flow control or flow limiters downstream of the meter
- Where vortex or corkscrew flow is expected, increase inlet and outlet sections or install flow straighteners.
- Where it is not practical to meet the required straight pipe runs for the flow meter, you may consider using flow conditioners or straighteners.
- Install two or more meters in parallel if the flow rate is too great for one Meter.
- Every flow meter installation should provide allowance for the expansion of the pipe work.
- Make sure there is sufficient clearance for installation and maintenance work to be done on the flow measurement system. When you see the space for work and maintenance in most practical installations, you wonder whether this point was ever considered at all
- To enable meters to be removed for servicing without station shutdown,provide a by-pass line
- Where possible provide proving connections downstream of the flow meter regular in-situ calibrations.
- Never install a flow meter on the pump suction side.