Flanges – Your Pipe Connection

Flanges act as mediators or connectors between two pipes or any kind of piping systems.

Breaking down Flanges

A flange is an external or internal rim or ridge, usually disc-shaped, which is joined onto an object so that it can be attached more effectively. Instead of welding or bolting two pipes together to create a seal, welding or bolting a flange to individual pipes allows the pipes or a pipework system to be moved in and out of position more easily.

Since moisture is a welder’s biggest problem, a flange may even be used in cases where a pipework system doesn’t need to be moved. A welder will tell anyone who lives next to the coast especially, “Once salt gets into your metalwork, it doesn’t come out easily”, so using flanges is a win, win.

The flange, along with the addition of an essential gasket, would form a pressure seal once bolted, threaded or welded together. This provides both support and strength to the join.

Pipe flanges are manufactured in different materials like stainless steel, cast iron, aluminium, brass, bronze, plastic or forged carbon steel and have machined surfaces. In most cases, the material chosen for the flange will be the same as the material used for the pipe or tube. Sometimes flanges like fittings and pipes for specific purposes, are internally equipped with layers of materials that are of a completely different quality to the flange itself. These are called ‘lined flanges’.

A stainless steel flange is highly resistant to corrosion and contain enough strength for even an industrial piping plan and forged flanges, most typically made from forged carbon steel, make access for cleaning, repairs, modification and inspection much easier.

Types of Flanges

Blind flanges – Also known as a blanking flange, these are used to seal off pipelines, valves or pumps and prevent flow. They are easily manageable and can be reversed to allow for expansion. They are suitable for testing the pressure of a gas or liquid flowing through a pipe. Blind flanges do not have a centre bore and can be supplied with or without hubs. They can sometimes be used as an inspection cover.

Slip-on-flanges – These are the least expensive flanges which have a diameter slightly larger than a pipe and come in small or large sizes, allowing them to easily slip directly over a pipe. Once put on, they are fillet welded to give strength and prevent leaks. There are two types – the ring and the hub.

Socket weld flanges – These are used for high pressure, smaller pipe applications such as steam lines. The pipe is inserted into the socket and fillet welded at the top, or hub of the flange which allows for smoother gas and fluid flow through a pipe.

Threaded pipe flanges – These have an outer thread and are beneficial as there is no need to weld them to a pipe. They are most commonly used for small diameter projects with lower pressure applications and are easy to assemble.

Weldneck flanges – These create smooth weld matching because their diameter is the same as the inside of the pipe thus reducing erosion and turbulence. Weldneck flanges are typically used for high-pressure and high-stress applications, working by transferring pressure from the flange to the pipe.

Lap joint flanges – These are typically used in conjunction with either a stub end or Taft. They are easily aligned and assembled and should be used for applications that require frequent reassembling and are at low pressure.

Ring-type joint flanges – These help to prevent leaks in high-pressure applications and have a unique groove that can be compressed onto a Blind, Slip-on or Weldneck flange. This addition further allows the pipe to withstand extreme temperature and pressure.

Steelmor is the leading supplier and manufacturer of stainless steel in South Africa and we stock a range of products suitable for many applications. We can also manufacture larger sizes to your unique specifications. Give us a call to find out how we can help meet your product requirements