In this article, I have tried to cover some of the special flanges such as Orifice flange, long weld neck flange, reducing and expanding flanges and flangeolet that used in piping and equipment.Special flanges are not as common as regular flanges. They are used to serve some specific function within the piping system.
Long Weld Neck Flange
Long neck flanges are used as a nozzle in the pressure vessel. Long neck has two advantages over the normal pipe to flange connection. First, it does not require pipe piece and second, it eliminates a but weld between pipe and flange that required in case of conventional nozzle connection. These types of flanges are normally used in very high pressure and temperature application. It is costly but gives high reliability and reduce fabrication efforts as compared to normal pipe to flange type nozzle.
ASME B16.5 covers the dimensions of the long weld neck flanges.
Orifice Flanges are used with orifice meters for the purpose of measuring the flow rate of either liquids or gasses. Pairs of pressure “Tappings”, directly opposite each other, are machined into the orifice flange.
Tap holes are either tapped ½” NPT or ½” NPS socket connection. A one tap from each flange is used to connect instruments with the help of tube that allows liquid or gas to reach the instrument. The other one is sealed with a plug.
Orifice flange comes in RTJ (Ring Type Joint) & Raised face type with different end types. Class #300 flanges are available in threaded, slip-on and weld neck end types. Orifice Flanges Class# 600 and above are available in only weld neck type end connection.
Image Source: www.flowmfg.com
In the image, you can see the complete orifice flange set. Orifice Plate, Gaskets, Pressure taps and Jack screw hole with two jack screws. These jack screws are drilled on the flange circle centreline at 90 degrees to the tapped hole and used to facilitate separating the flanges for inspection or replacement of the Orifice Plate and gaskets.
Orifice Flange Installation
Orifice flanges are installed in a straight run of pipe in order to avoid turbulence at the plate. As a rule of thumb, an orifice flange has ten diameters of straight pipe upstream and five diameters of straight pipe downstream. In general pressure taps kept at the same elevation to each other.
Image Source: idSolutions
Orifice flanges are available in Class# 300, 600, 900, 1500 and 2500-pound rating and the Dimensions are covered in ASME B16.36. Images show the installation setup of orifice flow meter.
Reducing flange is used in place of a standard flange to allow for a change in pipe size. This flange eliminates the need for a standard reducer in piping. The flange consists of one specified diameter with a smaller diameter bore size. Except for the bore and hub dimensions, a reducing flange has dimensions of the standard pipe flanges size and is considered an economical means to make a pipe size transition. There flanges available in weld neck, slip-on, and threaded end types. Reducing flanges are an economical way to make transitions between pipes of different sizes, however, due to high-pressure loss, they are rarely used in piping. ASME B16.5 covers the dimensions of the reducing flanges.
Image source: www.msmmfg.com
It is similar to weld neck flange but increases size of pipe to first or second larger size. It is alternative to using reducer and weld neck flange. Useful for connecting to valves, compressors, and pumps. These flanges are specially designed. Dimensions of the weld neck are in line with connecting pipe, other dimensions are in accord with standard ASME B16.5 flanges.
Image source: www.msmmfg.com
Flangeolet / Weldoflange / Nippoflange
Flangeolet is combination of olet (mainly weldolet or nipple) and flange. As you can see in the image that hub length is longer like long neck weld flange. It is 90 Degree branch connection use for high-pressure piping. It reduces the two weld joints than traditional Olet + Pipe + Flange connection and one weld joint in case of Olet + Flange connection. You can see the image of the flangeolet branch.