Guide To Flanges

Flanges are the connecting components bringing together Pipes, Pumps and Pressure Vessels. Most often flanges will be made of forged or cast steel, but are increasingly being manufactured in ‘hard’ and ‘exotic’ materials such as Inconel. This is an overview of the basic and most commonly found kind of flanges.

Weld-Neck Flange: Weld Neck Flanges are most often used for high pressure applications. Weld-Neck flanges have a long neck which is butt welded to a piping system, this neck transmits stressed to the base of the hub and to the wall thickness of the butt weld thus providing reinforcing the flange. The bore of the Flange will match that of the pipe which will reduce turbulence and erosion. Weld-Neck flanges are often used in piping applications with a number of repeating bends.

Slip-On Flange: The diameter of the Slip-On Flange is larger than the pipe so as it can ‘slip on’ to fit snugly. Though they are thinner than most other flanges but are welded both inside and out to increase their strength and prevent leakage. This design of flange is often used in preference to Weld-Neck Flanges as less accuracy is needed when cutting pipe to length.

Threaded Flange: Threaded Flanges are popular as they can be attached to a pipe without the need for welding. As their name suggests the bore of the flange is threaded, and most often will be fitted on pipes with a deep wall thickness. Although it may be advantageous to attach a flange without welding the applications are limited to relatively low pressure systems. This may be a good option for small pipes or where welding work may be considered dangerous.

Blind Flange: Blind Flanges are used to seal off the end of a pipe systems and prevent flow which in turn makes it easier to conduct pressure tests. Blind Flanges don’t have a bore and would be suitable for high temperature applications.

Socket Weld Flange: Socket-Weld Flanges are similar in design to slip-on, only are made with a counter bore to accept the pipe so as the diameter of the remaining bore is the same as the inside of the diameter of the pipe. Socket-Weld Flanges are attached through insertion of the pipe into the socket end and applying a fillet weld around the top. Most often used in high pressure systems such a steam lines, they may not be suitable for corrosive environments.

Lap-Joint Flange: Sometimes referred to as ‘Loose’ this type of flange has a radius at the intersection of the bore which is slipped over the pipe and will be used in conjunction with a Lap Joint Stub End. They are most commonly used in applications where the juncture does not come into contact with the fluid or gas and this makes them reusable and often used in applications where piping systems need to be dismantled quickly and easily.

B&B precision are an ISO accredited sub-contract manufacture based just off the M1, working to your drawing we can produce a wide range of components including bespoke and large diameter flanges. Email across your RFQs to: or call 01484866386


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