Orifice Performance

Principally, an orifice plate is a precision instrument. In best circumstances, the inaccuracy of Orifice plates can possibly fall in the range of 0.75-1.5% AR.


However, there are numerous error causing conditions which can terribly affect the accuracy of an Orifice plate…

Following factors are used to judge the performance of an Orifice plate:

  • Precision in the bore calculations
  • Quality of the installations
  • Condition of the plate itself
  • Orifice area ratio
  • Physical properties of the fluid flow under measurement

Further class of installation depends upon following factors

  • Tap location and circumstance. Generally, there are three ways to position a pressure tap.
  • Provision of the process pipe
  • Competence of straight pipe runs
  • Gasket intervention
  • Misalignment of pipe and orifice bores
  • Lead line design

Extra detrimental conditions consist of

  • Dulling of the sharp edge or nicks caused due to corrosion or erosion.
  • Warpage of the plate because of waterhammer and dirt.
  • Grease or secondary phase deposits on any of the orifice surface.

Any of the above said conditions has the tendency to affect the discharge coefficient of an orifice plate to a large extent


In case of metering systems with compliance to AGA 3, other measurement errors can occour due to internal surface roughness (i.e. as per AGA 3, if Beta ratio is 0,6 for a 10" line, minimum roughness shall be 34 micro inch and maximum 250 micro inches).

Apart from fiscal metering application, other things that can create measurement errors are relevant to installation: quantity of pipe curves before and after the element, lenght of upstream and downstream pipe, valves or other inline equipments, flow conditioners ect.