Flange's Definition And Types Of High Quality Flanges

By Author: kalpana pandey
Total Articles: 2
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A flange is used to connect different lengths of pipe, or to join a pipe to equipment such as pressure vessel, heat exchanger or valve. Flanges are joined by bolting with each other and sealing is accomplished with the use of gaskets. Flanges are connected to the piping with welding or threading.

There are various types of flanges available with different materials. The type and materialof a flange to be used depend on the service duty of theline. Service duty includes pressure, temperature and nature of fluid flowing through the line.

For process and utilities pipework, ASME B16.5, ASME B16.47 and BS 1560 are widely used international standards. API 6A is used for flanges for Welhead and Christmas Treeequipment used in Oil and Gas industries.

1. Types of flanges

a. Weld-Neck Flange (WN)

The WN flange is butt-welded to the pipe. WN flanges are typically used on sever duties such as high pressures and/orhazardous fluids.

b. Socket Weld Flange (SW)

Socket weld flanges are often used on high pressure, hazardous duties but will be limited to a nominal pipe size (NPS) of 1-1/2 inches. ...
... The pipe is fillet welded to the hub of the SW flange.

c. Slip-On Weld Flange (SO)

Slip-On weld flanges are used typically on low pressure and low hazard services such as fire water, cooling water, etc. The pipe is welded both to the hub and the bore of the flange.

d. Lap Joint Flange

Comprises of a hub or “stub end” welded to the pipe and a backing flange or capped flange which is used to bolt the joint together. This type of flanges are used typically in high alloy piping, where piping and hub are manufactured from high alloy while the flange is manufactured from Carbon Steel. This is cheaper than complete alloy flange.

e. Long Weld Neck flanges

Long Weld Neck Flanges are basically an extension of welding neck flanges and have straight hubs of uniform thickness. They are widely used on nozzles of high pressure heat exchangers and pressure vessels.

f. Blind Flanges

This is a flange without a bore and is used to shut off a piping system or vessel opening. These types of flanges are also used on inspection openings or manholes of the pressure vessels and heat exchangers.

2. Types of flange facings

a. Ring Type Joint (RTJ)

This type of facing is used on the most sever duties, for example high pressure gas piping and Flanges having pressure rating of CL 900 and above. Ring type metallic gasket must be used on this type of flange facing. The seal is affected by metal to metal contact between the gasket and the flange groove. The surface finish of gasket groove shall not exceed 1.6 µm (63 µin).

b. Raised Face (RF)

Sealing on a RF flange is achieved by a soft non-metallic gasket, which fits within the bolts of the flange. The raised face should have either a serrated concentric or serrated spiral (gramophone) finish having a resultant surface finish from 3.2µm to 6.3 µm (125 µin to 250 µin). The seal is affected by compressing the gasket material and causing it to flow into the grooves on the flange facing. Under no circumstances should flange sealing surfaces be machined in a manner that tool marks would extend radially across the sealing surface. Such tool marks are practically impossible to seal regardless of the type of gasket used. This type of facing is used in medium severe duties, for example up to 600 Class flanges.

c. Flat Face (FF)

Sealing is achieved by compression of a flat non-metallic gasket between the gramophonic or concentric grooved surfaces of the mating flanges similar to the RF flanges. The gasket fits over the entire face of the flange. FF facings are normally used on the least severe service duties such as low pressure water drains. With this facing, contact area of the gasket is larger which reduces flange bending.