Copper Nickel Slip On Flanges actually slip over the pipe. The pipe flanges are typically made with an inside diameter of the pipe flange slightly larger than the outside diameter of the pipe. This allows the flange to slip over the pipe but to still have a somewhat snug fit. Slip-on pipe flanges are secured to the pipe with a fillet weld at the top and the bottom of the slip-on pipe flanges. These pipe flanges are also further catagorized as a ring.