Pipe Flanges: Applications, Types and Flange Ratings

Pipe flanges are disc-shaped fittings that are commonly used to build piping systems. Flanges can add support to a pipeline, close or block an existing pipeline, or they can be used for creating joints and attaching additional pieces to the system. When connecting to a system, flanges can be bolted or welded together, and there are 6 basic types of flanges that are used for different piping systems.

In plumbing, for instance, flanges are often used to build and connect plumbing pipelines, and they’re also used to connect fixtures to the water supply. Toilets all commonly use a special type of flange called a toilet flange, and there are also flanges designed for showers and sinks.

Pipe Flange

Aside from plumbing, flanges are commonly used in industrial settings where pipelines are necessary. For instance, flanges are a common piece of hardware in the oil and gas industry, as well as in chemical production plants.

 6 Basic Types of Flanges

Although there are many different types of flanges that are used for a variety of pipeline projects, there are six that are the most common.


  • Slip-On Flange: A slip-on flange is slightly larger in diameter than the pipe, enabling the flange to “slip on” to the pipe. This creates a tight fit with the pipe. Compared to other flanges, the slip-on is slightly thinner and has a shorter lifespan than other flanges, but they are dependable and cost effective.
    Slip-On Flange



  • Threaded Flange: Threaded flanges are similar to slip-on flanges. They slide over a pipe, but no welding is required. This is the biggest advantage of threaded flanges. They’re often used for smaller pipes and in areas where welding would be dangerous. Because there is no welding, the threaded flange is typically used in low pressure systems.

    Threaded Flange

  • Socket-Weld Pipe Flange: The socket-weld flange is used in smaller-sized, high-pressure pipe systems. These flanges are inserted into the pipe and attached with a fillet weld, which enables a better gas flow through the pipe.

    Socket-Weld Pipe Flange

  • Lap Joint Flange: Lap joint flanges are similar to slip-on flanges, but they do not have a raised face. In terms of pressure holding, these are more commonly used with low pressure systems.
    Lap Joint Flange



  • Welding Neck Flange: These types of flanges are used in high-pressure systems, and they’re used to take stress off the pipe system. The welding neck flange has a neck that is welded to the pipe base, and due to this they provide more strength to the fitting. This type of flange is considered a “low turbulence” flange, because it increases flow.

    Welding Neck Flange

  • Blind Flange: The blind flange is used to seal off a pipe system. Usually, they are also incorporated into a system to provide fast access to the interior of the system or to stop the flow.

    Blind Flange

Determining Flange Ratings

All flanges are rated according to their pressure rating and based on standards set by the ASME. Current ASME standards B16.5, used for normal pipe sizes between ½” and 24”, and B16.47, normal sizes above 24” call for flanges to be made out of forged metals.

Flanges are also rated by pressure class, set by the ANSI. For B16.5 flanges, there are 7 pressure classes, 150, 300, 400, 600, 900, 1500 and 2500, which are based on the material the flange is made of and other dimensional factors. This measure doesn’t refer to the psi that the flange is designed to handle; for instance, the maximum pressure in psi for the Class 150 flange is 290 at temperatures below 100 degrees.

The type of flange that you choose depends, of course, on the type of work that you are doing. Flanges used in the oil and gas industry are required to be stronger and handle greater levels of pressure. Plus, the type of flange, including the weld or bolting can contribute to ASMI rating.

Find the best prices on industrial and plumbing pipe flanges at Deelat.com. We offer a variety of affordable flanges, including slip-on, welding neck, socket weld and blind flanges. We guarantee some of the lowest prices for ASMI- and ASME-rated flanges on the web.

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