Pipe Flanges

Pipe Flanges

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 Flange
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.

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.
  • Blind flanges are solid circles used to block off piping. 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.
  • Slip-on flanges are designed to prevent leakage. They are welded inside and out and provide a good substitute for welding necks when cost and space is limited.
  • Socket weld flanges are used in smaller pressure systems. They are created to enable a pipe to be inserted and welded into place.

Flange Facing
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: 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.

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 appropriate raised face flange to use during assembly.

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.