Flow Instruments

To ensure proper flow meter selection, correct process data as below shall be provided for minimum

Fluid phase,
Flow rate,
Viscosity ,

Normal and maximum design conditions as well as for alternative operating modes
Abnormal operating conditions such as start-up, commissioning, regeneration, emergency

In-line flow meters are preferred for flow rate measurements if the benefits of initial investment, wide turn down, high accuracy and low maintenance requirements outweigh the extra effort and risk associated with proper sizing and selection

Orifice or any other types of differential pressure based flow measurement are preferred for flow rate measurements for low cost and low maintenance issues.

Unless special considerations such as required size, pressure rating, accuracy, turn-down, permanent pressure loss low Reynolds Number, avoidance of obstructions in the piping, etc., make it necessary to apply other in-line flow measuring techniques in the order of preference

The following general installation requirements apply

  1. The installation requirements (including the minimum straight length requirements) of pressure differential devices such as orifice plates and venturi tubes shall be in accordance with ISO 5167-1. For other types of flow measurement, the Manufacturer’s guidelines with regard to maintenance requirements shall be followed carefully. The straight length shall be free of protrusions from gaskets, welds etc.

  2. Eccentric pipe reducers have proven to severely disrupt the velocity profile and should therefore not be used in the vicinity of velocity profile dependent flow meters.

NOTE: Concentric reducers with sufficient constriction (Downstream/upstream £0.7) have a strong remedial effect on asymmetry and uniformity of velocity profile, but not on swirls.

  1. To avoid extremely long upstream straight lengths, control valves should be located downstream of the velocity profile dependent measuring elements wherever possible. Where isolating valves are located upstream of the measuring element, they should be located outside is’ required type (e.g. gate valves or ball valves) and fully open under normal plant operation.

  2. Liquid meters in horizontal lines shall not be installed at the highest piping point where gasses are likely to collect and hard to remove.

  3. For liquid services, the horizontal or vertical flow line must remain full under all operating conditions.

  4. Gas meters in horizontal lines shall not be installed at the lowest piping point where liquids are likely to collect and hard to remove.

  5. Choose a location with minimum pipe vibration. If necessary, support the pipe at either end of the meter to prevent excessive movement.

  6. The inner diameter of the gasket shall exceed the inner diameter of the meter/meter run. Select a gasket type that is centered by its outer ring. An inner ring should prevent soft material from protruding into the pipe, causing flow pattern disturbance.

  7. If pressure and/or temperature measurements are required for density compensation, the pressure tapping and thermowell should be located at two and a half (2 ½) pipe diameter upstream and eight (8) pipe diameters downstream of the meter respectively.

  8. The vendor may or may not allow the electronic parts (e.g. sensors) to be enclosed by heat-insulation materials. Extensions meant to keep electronics at a moderate temperature shall not be thermally insulated shall be complied with.