Definition and details of flanges

WHAT ARE SPECIAL FLANGES

On this page are the special flanges discussed, and parts that may include a flange connection. Special Flanges are basically identical to standard flanges, but have a number of special features.

ORIFICE FLANGE

Orifice Flanges are intended for use instead of standard pipe flanges when an orifice plate or flow nozzle must be installed. Pairs of pressure "Tappings", mostly on 2 sides, directly opposite each other, are machined into the orifice flange. This makes separate orifice carriers or tappings in the pipe wall unnecessary.

IMAGE of set of Orifice Flanges.

On the image above a set Orifice Flanges is shown, where the tappings are sealed with a plug, and where a jack screw is machined. This jack screw is used to facilitate separating the flanges for inspection or replacement of the "Orifice Plate" and gaskets.

The range of orifice flanges covers all standard sizes and ranges, and all common flange materials. Flanges are available in Welding Neck, Slip On, and Threaded form, and are typically supplied with two ½" NPT tappings in each flange.

ASME B16.36 covers Dimensions and dimensional tolerances from orifice flanges (similar to those covered in ASME B16.5) that have orifice pressure differential connections. Coverage is limited to the following flanges:

• Welding Neck Classes 300, 400, 600, 900, 1500, 2500
• Slip On Class 300
• Threaded Class 300

ORIFICE PLATE

A Orifice Plate is typically a circular, flat plate with a handle. The most common orifice plate is the square-edged concentric bored orifice plate, others are Eccentric Orifice Plate, Segmental Orifice Plate etc. and typically, it is made of a durable metal such as stainless steel.

IMAGE of a concentric orifice plate.

They are normally mounted between a set of Orifice Flanges and are installed in a straight run of smooth pipe to avoid disturbance of flow patterns from fittings and valves.

The image of a CROSS-SECTION of a set of Orifice Flanges, gives you a good impression.

Orifices Plates are used to create a differential pressure that relates to the velocity of the gas from which a flow rate can be calculated. As the following gas passes through the restriction in the line caused by the orifice plate, the difference in the upstream and downstream pressure can be measured at set points, called taps, and a flow rate at the point can be determined. As the plate serve as a restriction in a pipeline, then we talk about a Restriction Orifice Plate, abbreviated (RO).

Concentric Orifice Plate
The most common orifice plate is the square-edged concentric bored orifice plate. The concentric bored orifice plate is the dominant design because of its proven reliability in a variety of applications and the extensive amount of research conducted on this design. The concentric plate is also easily reproduced at a relatively low cost.
The concentric orifice is used to measure a wide variety of single phase, liquid and gas products, typically in conjunction with flange taps.

Eccentric Orifice Plate
Eccentric orifices are used to measure the flow fluids that carry solids and are also used to measure gases which carry liquids. With the eccentric orifice at the top of the plate, it can measure liquids that carry gas. It should be noted that the eccentric orifice has a higher degree of uncertainty as compared to the concentric orifice.

Segmental Orifice Plate
Segmental orifice plates are used to measure the flow of light slurries and fluids with high concentration of solids. The design of segmental orifice eliminates the damming of foreign matter and provides more complete drainage than the eccentric orifice plate. The segmental orifice is considerably more expensive than the eccentric orifice and has slightly greater uncertainty.