Why Orifice Drain hole Required ?

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Where the gas flow is constantly wet, the orifice plate does not require a drain hole. However, a drain hole is suitable where some liquid is introduced into the Pipeline for a short time, but after that, the gas flow dries up. There is no need for wet-gas measurement in this case; The problem is that during the period in which some liquid flows, a pool of liquid will form against the upstream face and thus metering accuracy will also be reduced The time when the flow is dry. Another installation where a drain hole was found suitable was the one where without the drain hole very important accumulation of dirt was; A new orifice plate with a drain hole allows smaller particles of Dirt to pass the plate and so problem solved.

The drain-hole provides a liquid bypass in the solution, plate allowing the fluid to Stream of gas to pass through the plate. While drain-hole plates are a cost-effective way of measuring gas with very low liquid content, they are not as accurate in Single-phase flow as standard design. Since there is no limit to this inaccuracy Well documented and the current formula as the industry is skeptical, the drain-hole plates are not used as widely as they could be: so the new data there is a need to instill confidence in their use.

ISO/TR 11583:2012, Covers wet-gas flow using orifice plates without a drain hole. There is no accepted correlation for orifice plates. Wet gas has drain holes, and probably doesn’t need one. in multiple wet-gas flows, Most of the liquid will pass through an orifice plate with a drain hole

The figure shows a picture of an orifice plate with a drain hole. The plate is fitted Between the flanges using bolt holes around the plate perimeter. The dashed line seen in Figure 1 marks the region of the plate that is in contact with fluid within the pipe. A smooth circular through plate located at the bottom of the drain hole aligned with the bottom edge of the pipe and with the bottom of the hole upstream pipe. The top edge of the drain hole should be sharp. The diameter of the downstream pipe on the orifice plate should be very similar Upstream Pipe: If the downstream pipe was much smaller than the upstream Will partially or completely block the drain hole. Upstream alignment pipe, orifice plate, and downstream pipe are especially important when having a drain hole: for example, the dowel holes in picture 1 achieve this alignment. There is a desire within the industry to use orifice plates with drain holes, but ISO/TR 15377:2007 [2], the only reference document, a very simple and based on a Theoretical model.

Drain hole standard

Drain hole standard

Establishing a drain hole can be equated to increasing the area of ​​the hole in a predictable way: an equation is given in ISO/TR 15377:20018. However, recent data from this chapter suggests that the existing drain-hole equation in ISO/TR 15377:20018 is unsatisfactory. The data for the drain hole has a surprisingly strong dependence on the peripheral location of the pressure tapping, although there is little dependence on the Reynolds number. A new analysis is presented based on the assumption that, although the differential pressure is perturbed by the presence of the drain hole, the discharge coefficient of the orifice (as distinct from the drain hole) is unaffected by the presence of the drain hole provided that the mean gap is around the pipe. pressure is used. On this basis, an equation is drawn for the correct hole diameter taking into account the drain hole. However, it is highly desirable to amend ISO/TR 15377:2007, given that for the data collected here, flow errors from its equation up to about 2% in magnitude while the new equation has errors of less than 0.25% in magnitude.

What is the purpose of the orifice drain hole?

A drain hole is a small hole provided at the bottom area of ​​the orifice plate.

Gas flow service requires drain holes where liquid can become trapped. The size of the drain hole can affect the accuracy of the flow measurement. However, if the diameter of the drain hole is less than 10% of that of the orifice, the unmeasured flow is less than 1% of the total flow. Drain holes in dirty fluid service or slurries are not recommended because the hole can be plugged. In this application, the use of an eccentric orifice plate becomes optional.

drain hole1

What is the purpose of a hole punch?

A vent hole is a small hole provided in the upper area of ​​the orifice plate.

drain hole2

Liquid flow service requires vent holes where gas can enter. The size of the vent hole can affect the accuracy of flow measurement. However, if the diameter of the vent hole is less than 10% of that of the orifice bore, the unrated effluent is less than 1% of the total effluent.

Dirty fluid service or a vent hole in the slurry is not recommended because the hole can be plugged.

In this application, the use of an eccentric orifice plate becomes optional.


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