General Information
A Flange is a method of connecting pipes, valves, pumps and other equipment to form a pipe work system. It also provides easy access for cleaning, inspection or modification. Flanges are usually welded or screwed into such systems and then joined with bolts.

Flange Types

Weld Neck

This flange is circumferentially welded into the system at its neck which means that the integrity of the butt welded area can be easily examined by radiography. The bores of both pipe and flange match, which reduces turbulence and erosion inside the pipeline. The weld neck is therefore favored in critical applications


Slip On

This flange is slipped over the pipe and then fillet welded. Slip-on flanges are easy to use in fabricated applications.



This flange is used to blank off pipelines, valves and pumps; it can also be used as an inspection cover. It is sometimes referred to as a blanking flange



Socket Weld

This flange is counter bored to accept the pipe before being fillet welded. The bore of the pipe and flange are both the same therefore giving good flow characteristics.



This flange is referred to as either threaded or screwed. It is used to connect other threaded components in low pressure, non-critical applications. No welding is required.



Lap Joint

These flanges are always used with either a stub end or taft which is butt welded to the pipe with the flange loose behind it. This means the stub end or taft always makes the face. The lap joint is favored in low pressure applications because it is easily assembled and aligned. To reduce cost these flanges can be supplied without a hub and/or in treated, coated carbon steel.



Ring Type Joint

This is a method of ensuring leak proof flange connection at high pressures. A metal ring is compressed into a hexagonal groove on the face of the flange to make the seal. This jointing method can be employed on Weld Neck, Slip-on and Blind Flanges.



1.JPGWeld Neck Flanges - ANSI B16.5

Class 150 Ib

Class 300 lb

Class 600 Ib


1Slip On Flanges - ANSI B16.5

Class 150 Ib

Class 300 lb

Class 600 Ib


Blind -Flanges - ANSI B16.5

Class 150 Ib

Class 300 lb

Class 600 Ib


Socket Welding Flanges - ANSI B16.5

Class 150 Ib

Class 300 lb

Class 600 Ib


Flange Facings - BS 4504

BS 4504 flange facing types A to H are defined below. The dimensions vary with pipe size (DN) and pressure rating (PN) as detailed in the following table.




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