Pipe flanges are metal connectors used to connect pipes, valves, pumps and other parts of a piping system. They provide an access point for inspections, cleaning, and repairs. Pipe flanges are usually welded or screwed to a pipe then bolted into place.
Pipe flanges can be described as collars, discs or rings designed to provide extra support, allow for additional attachments and block off piping. There are numerous styles of pipe flanges, each made from a variety of materials. Some popular styles are aluminum flanges, plated flanges, tank flanges, steel flanges, plastic flanges and galvanized flanges. The most commonly used material is carbon steel.
Standard flange designs include threaded flanges, lap joint flanges, welding neck flanges, blind flanges, slip-on flanges and socket weld flanges.
Standard Flange Designs
- Threaded flanges are manufactured in accordance to the pipe size. Threaded flanges are used in low-pressure applications or in situations where welding could be problematic.
- Lap joint flanges are applied in systems that require periodic inspection and maintenance. They are bored a bit larger than the outer diameter of the pipe to allow for insertion. Lap joint Flanges often times are used with Stub End Fittings.
- Blind flanges are solid circles used to block off piping or pressure vessels. These applications are also good for allowing access to the piping system when maintenance work needs to be performed. Another use for these flanges can be pressure testing of gas or liquid because they are excellent at handling high pressure. They have holes drilled around the outer portion of the circle. Their drill pattern is designed to match that of their companion flange.
- Welding neck flanges are designed with high necks, perfectly suited for welded joint connections. They are bored to the interior diameter of the pipe because the inside diameter of the flange is made to match the inside diameter of the pipe. Welding neck flanges help with the maintenance of stress because the welded design helps to transfer stress from the flange to the pipe and it reduces the concentration of stress at the hub.
- Slip-on flanges do exactly what their name implies, they slip-on over the pipe. The diameter of the outside of the pipe is made to be a little smaller than the diameter of the inside of the pipe so they can still have a snug fit. These flanges are designed to prevent leakage. They are welded inside and out and provide a good substitute for welding necks when cost and space are limited. Slip-on flanges can be subcategorized as rings or hubs.
- Socket weld flanges are used in smaller pressure systems. They are created to enable a pipe to be inserted and welded into place. This design allows for a smooth flow of the gas or liquid as well as a smooth bore.
These are the six most common pipe flange designs, however, there are people that custom manufacture pipe flanges so that they can meet the requirements of projects of all types. Various specifications that provide dimensional information, as well as pressure specifications at different temperatures, have been written and published by many organizations and associations. These pressure and temperature specifications help people choose a pipe flange that will make their project a success.
The facing of a pipe flange is particularly important. Flange facing involves machining the flange mating surfaces to ensure a dependable, leak-proof seal during pipe assembly. Some of the most popular flange facings are a flat face, raised face and ring type facing.
Flat Face Flange
Flat face flanges have flat surfaces, meaning they have no ridges. Their gasket surface and the bolting circle face are on the same plane. A flat face flange should not be bolted to a raised face flange; therefore, when a cast iron flange is connected to a carbon steel flange (A/SA 105), the raised face on the carbon steel flange (A/SA 105) must be removed prior to assembly. These flanges are typically used when the mating flange or the flanged fitting is made from a casting.
Raised Face Flange
Raised face flanges are the most commonly used type of flanges. A raised face flange has a raised ridge around the bolt circle. The ridge height varies depending on the weight rating of the raised face flange. A dimensioning chart may be used to determine the appropriately raised face flange to use during assembly. Raised face flanges help to increase the amount of pressure that the joint can contain. This is done by concentrating more pressure on a smaller gasket area.
Ring Type Facing
A ring-type facing flange often has a raised face with a ring groove. Ring type facing flanges can provide a reliable seal that is resistant to vibrations and extreme temperatures. Ring type facing is commonly used in high pressure and/or high-temperature conditions. They are ideal for use in pipeline designs.
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