Design considerations for orifice plates

When choosing your dP flow measuring element, take these factors into consideration:
1. Flow range (also known as turn down)
2. Pressure and Temperature
3. Line size
4. Pressure loss
5. Medium corrosiveness
6. Medium abrasiveness
7. Location, straight lengths
8. Required performance
9. Service
We love to help you with these considerations. Together we perform a flow calculation according to ISO 5167-1 using software simulation. This gives a grip on the effect of changing parameters and can help:
• choosing the right measurement principle / flow element
• reaching a carefully considered compromise
• get a predictable measurement uncertainty
• understand whether calibration is advisable or mandatory

Eccentric orifice plates

Concentric orifice plates are not suitable for dirty fluids, because dirt can accumulate against the plate. Eccentric and segmental orifice plates are designed such that solids can pass through the bore. [illustratie] [link naar stoom applicatie] The same is the case for condensate, when measuring wet gases like steam.

Segmental orifice plates

These type of orifice plates often have a conical or quarter-circle type aperture. Useful when measuring liquids which have a high viscosity and a low velocity. Especially in even more extreme conditions as with eccentric orifice plates. A disadvantage is that this type is not prescribed in the ISO-5167, which makes calibration necessary. Another type of flow measurement may be the better solution.

Restriction orifice plates and multi-stage plates

Orifice plates are sometimes designed to fit between flanges that have ring-type joints (RTJ). The cross section profile of the plate is designed to fit inside the recess of the RTJ flanges and is used as flange sealing. [illustratie]

PVDF coupling

Aluminium coupling

The specifications of orifice plates

The standard materials used (by our manufacturer SEIKO) for orifice plates is stainless steel according to ASME A240 316/316L. Other materials can be used as well including Duplex Steel and ASME A182 F91.
The plate thickness is selected based on the application and design conditions, typically between 3 mm (0,12 inch) to 10 mm (0,4 inch).
The flow calculation is performed according to the ISO 5167- Part1, Teesing uses Conval for that purpose. [vraag: wordt de uitkomst van de berekeningen gedeeld met de klant, of alleen de tekening? Geeft de klant akkoord op de berekening/tekening voor bestelling?]
The typical uncertainty of uncalibrated orifice plates is +/-0,5%.
The generated differential pressure is needed to measure flow, but is in itself unwanted. A part of the pressure loss however is regained after a certain amount of pipe length. The actual permanent loss depends on the Beta-ratio and is typically 45-90% of the differential pressure. The lowest possible permanent pressure loss is obtained with a venturi flow element. [link naar uitleg open area ratio, Beta]