1.Introduction – Installing an Orifice Meter
At the end of this post you will find the EMERSON document who explains the basic orifice plate installation guidelines, including:
- orifice plate tap orientation
- orifice plate tapping locations
- orifice tapping
This post is mainly a set of rules for the orifice plate installation like an orifice flow meter installation guidelines. In order that a flow instrument may accurately read flow, it’s necessary that the installation comply with certain rules.
Follow the recommendations regarding elimination of flow disturbances, and the general layout and piping data.
The section of the pipe in which the primary element is installed mat be horizontal, inclined or vertical. The direction of the flow is immaterial except when a foreign substance such as sediment or vapor is carried in suspension.
In this case it is preferable to install the primary element in vertical section of the line with the flow in such a direction that the foreign substance will readly carry on trough the primary element, i.e. upward in the case of vapor and downward in the case of sediment.
2.How an Orifice Plate Works? What is an Orifice Plate?
3.Flow Disturbances and Recomendations
The Orifice Meter must be installed in the proper orientation relative to the pipe and the fluid measured.
Pipe fittings and valves upstream from the primary element generate swirls and crosscurrents, which if uncorrected by a straightening vane may considerably upset the flow measurement. For accurate measurement the use of straightening vanes is usually imperative; however, if we are mainly concerned in the comparison of relative values or in control, vanes may be unnecessary.
Also, if the only source of disturbance is a single bend, ell, tee, or reducer preceding the orifice plate run, straightening vanes effect no improvement.
Orifice Plate Installation Straight Run Requirement
To be able to have the required precision, it is necessary that our pipe has a previous straight run long enough to avoid disturbances in the fluid that will change in the flow profile that the orifice plate receives. It is possible to reduce the straight run length but it will surely affect the final accuracy of the orifice meter.
A. Straightening Vane IS NOT used
For the various types of upstream disturbances liested bellow, allow the recommended minimum distances of straight pipe between the disturbance and the upstream pressure tap.
- Flanges, collars, wide-open gates, reducers or bends, elbows or tees which are all in the same plane – 10 pipe diameters
- Angle turns in two planes – 50 pipe diameters
- Pressure regulator, control valve or similar apparatus or fitting – 75 pipe diameters
B. Straightening Vane IS used
If a straightening vane is empluyed, 10 pipe diameters of straight pipe preceding the upstream pressure tap and 5 following the downstream tap will be sufficient. The outlet face of the straightening vane should be located 6 or more pipe diameters upstream from the upstream pressure tap regardless of the type of pressure connections employed, but not closer than 4 pipe diameters to the nearest upstream disturbance.
C. Minimum Straight Run Lenghts for Orifice Runs and Other Flow Elements in Accordance with ISO 5167-2
General Installation requirements:
- The orifice meter must be installed between two mating flanges in the pipe.
- For liquid metering, the pipe should run full at the measuring section.
- The diameter of the tube must be circular over the measured length.
- The internal surface of the measuring pipe must be clean and free of scale, pitting and deposits or any other possible source of turbulence.
- The pipe and pipe flanges should be lagged for orifice plate steam applications.
The minimum recommended lengths for upstream and downstream for optimum accuracy are shown below. Shorter lengths can be used, although this will reduce the accuracy of the system.
4.How to install orifice plate in pipeline?
4.1.Horizontal Installation Guidelines
A) Horizontal Installation for Clean Fluids
With an horizontal line, the pressure connections should be made at the SIDE of the line to allow trapped vapors to escape from the connectiong lines, and to prevent sediment from enterinf in these lines.
The following instructions apply for the layout of the orifice plate and transmitter when liquid flow is to be measured:
- The pressure tappings should be horizontal or up to 45° below the horizontal.
- They must never be taken off from directly below the orifice plate as any dirt from the pipeline may fall into the impulse piping and either block it or cause a serious error in the transmitter reading.
- The two impulse pipes should follow the same route, preferably clipped together.
- The transmitter should be installed at a lower position than the orifice plate.
B) Horizontal Installation for dirty or corrosive Fluids using a seal
If liquid being measured must not come in contact with transmitter, 3/8 inch tubing and transmitter body must be filled iwht suitable seal liquid. The 2 filling tees must be at same elevation.
C) Horizontal Installation for clean noncondensable gas
The following instructions apply for the layout of the orifice plate and transmitter when gas flows are being measured.
Allowing moisture to drain out and not fill the impulse piping.
The position of the pressure tappings shall be vertical or within 45° of the vertical:
The Pressure Transmitter should be installed at a higher position than the orifice plate.
The two impulse pipes should follow the same route, preferably clipped together
D) Horizontal Installation for vapor or dirty or consensable gases
- The following instructions apply for the layout of the orifice plate and transmitter when steam flow is being measured.
- The position of the pressure tappings shall be horizontal or up to 45° above the horizontal.
- The DP Transmitter should be installed at a lower position than the orifice plate.
- The impulse lines should be filled with condensed water to prevent damage to the transmitter.
- Temperature at the measuring cell should be less than 100°C.
Can we install orifice plate in vertical line? Yesss
If the orifice plate can not be installed in a horizontal process pipe, we must follow the following recommendations.
4.2.Vertical Installation Guidelines
Depending on the orifice plate installation direction the impulse piping should be set up as shown below :
In the case of having a ascending fluid, the impulse piping must be configured as shown below. The difference in the static head pressure can be compensated using the zero adjustment on the pressure transmitter.
In the case of having a descending fluid, the impulse piping must be configured as shown below. The difference in the static head pressure can be compensated using the zero adjustment on the pressure transmitter.
A) Vertical installation for clean liquids
B) Vertical installation for dirty or corrosive liquids
Mount the transmitter LOWER than the pressure connections.
C) Vertical installation for clean noncondesable gases
Vertical installation for vapor condensable gases or dirty gases
- Orifice Plate Installation Drawings from Foxboro Co.
- BRISTOL BABCOCK (1989) Flowmeter Applications
- SPIRAX SARCO (1997) M410 Orifice Plate Assemblies
- EMERSON (2014) Rosemount 1495 Orifice Plate, 1496 Orifice Flange Union