Slip on flanges are a type of pipe flange commonly used in low-pressure applications. They are designed to allow the pipe to slide into the center of the flange for welding around both the outer diameter of the pipe and the interior of the connection. This type of flange is a great alternative to weld neck flanges because it does not have a weld bevel, which allows for more flexibility in adjusting the length of the pipe relative to the flange. The bore of the slip on flange provides ample space for the pipe, making it easier for welders and fabricators to make the connection.

Most slip on flanges have a hub, which can be similar in dimension to a raised face. However, slip on flanges can also be furnished without a hub if space is limited or a "ring style" slip on is desired. Slip on flanges in higher pressure classes are often made with a lap joint height for a better connection. If the hub height is not a concern and a lap joint is not readily available, slip on flanges can be made to a lap joint style with a machined hub.

While slip on flanges are suitable for low-pressure applications, they may not be the best option for high-stress services that require a stronger connection. Weld neck flanges, which have a reinforced hub at the base and form a weld bevel connection directly to the butt weld end of a pipe, are often preferred in these situations. The tapered hub of a weld neck flange provides stronger mechanical stress service.