Orifice Meters
Orifice meter tubes are differential pressure estimation devices and commonly used in gas and dry steam service. Orifice meter tubes shall not be used in liquid service, polisher gas service, or gas service with farranging surging in flow rates. Accuracy is +/-.25% of rate in a calibrated tube,and +/-0.60% of rate in not calibrate tube.
"Differential Pressure"
The minimum rating of orifice flanges shall be 300 Ansi. The minimum size of orifice plate flanges shall be 50mm nominal piping. Differential pressure taps shall be 1/2" Fnpt.
Orifice plates shall be square-edged concentric type (316 stainless steel). The beta ratio range shall be between 0.20 (minimum) and 0.67 (maximum). Weep and orifice vent holes shall not be utilized, unless specifically authorized otherwise.
All flow transmitters and pressure transmitters shall be direct related without impulse lines, and static pressure shall be taken downstream of the orifice plate. Differential pressure (Dp) shall be sized such that the general compose flow shall be 65% to 75% of the flow scale. The beloved flow scale is 0-25 kilo Pascal.
There will be cases where the beloved flow scale of 0-25 kilo Pascal cannot be achieved, then the following Dp ranges shall apply:
- 0.344 barg =< operating pressure < 2.1 barg 0-5 kilo Pascal
- 2.1 barg =< operating pressure < 4.8 barg 0-12 kilo Pascal
- 4.8 barg =< operating pressure if not 0-25 kilo Pascal, then 0-50 kilo Pascal, or 0-100 kilo Pascal
Orifice fittings in applications where wide ranges of operating conditions are encountered, or frequent inspections of orifice plates are required shall have senior orifice fittings, to allow turn out of orifice plates under pressure. Junior fittings may be used where flow rate turn down conditions are not as demanding such as fuel gas to turbines, and or blanket gas systems.
Senior or junior orifice fittings shall be supplied with upstream and downstream tubes.
Custody change meter tubes shall meet the requirements. Meter tubes shall be provided with an upstream-approved flow conditioner, settled 7.5 nominal diameters upstream of the orifice plate. Any piping taps upstream of the flow conditioner shall not be closer than 900mm. The downstream pressure and climatic characteristic taps shall not be closer than five nominal pipe diameters from the orifice plate.
Custody change meter tubes shall come with upstream and downstream weld neck flanges to facilitate inspection of the internal diameter. The flow conditioner shall also be flanged. Meter tubes shall meet the piping requirements of the scheme piping specification, the painting requirements of Dep 30.48.00.31-Gen "Painting and Coating of New Equipment", and fabrication requirements of Dep 31.38.01.31-Gen "Shop and Field Fabrication of Steel Piping".
For non-custody change applications, the meter tube required nominal upstream length is 17.5 pipe diameters and 5 nominal pipe diameters downstream. The nominal turn down ratio of an orifice plate meter is 4.0 to 1.
Orifice Meter In Oil And Gasdifferential pressure monitor
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