Slip on flanges usually “slip” over a pipe and are welded in place. This allows the flanges to swivel freely to easily align bolt holes prior to installing and welding in place.

Flanges are most often used to connect pipes that have diameters of more than 2 inches. The flange’s joint consists of two matching disks of metal, separated by a gasket, that are bolted together to achieve a secure seal with the gasket material.

The flange is attached to the pipe by screwed fittings. The flange uses force provided by the bolts to pre-load the gasket. When the internal pressure is applied, there is enough contact stress between the flanges and gasket to maintain a seal.

#1 Check the flange and pipe to make sure there is no damage that may prevent a proper seal from being formed.

#2 Slide the slip-on flange onto the pipe using your hand. Determine where you will be welding the flange to the pipe. In most cases, you will be welding the flange to the end of the pipe.

#3 Use a welder to weld the inside and outside of the flange to the pipe. This will create a strong seal between the pipe and flange.

#4 Perform a pressure test to ensure the welded seal does not leak. Turn on the water leading to the pipe and observe the pipe for any leaks.