A flange plate is a flat, circular disk that is welded onto the end of a pipe and allows it to be bolted to another pipe. Typically used in fuel and water pipelines, the two flange plates will be bolted together with a gasket in between them. The flange plate will have bolt holes all around the perimeter and will be used to create junctions, tees and joints.
When building a pipeline, the length of the pipes used are not always known. By manufacturing the pipe separate from the flange plate, the welders can cut the pipe to length and weld a flange plate in place to join the pipes at any needed length. The plates can also be welded to the pipe on a slight bias, allowing two pipes to be joined that may not be precisely lined up.
Flange plate designs are uniform in any given size regardless of materials used to create them. This allows a 6-inch (15 cm) black pipe flange to mate perfectly with a 6-inch stainless steel flange. The flange plates will have a serrated finish on the inside mating surface, which allows the plate to seat into the gasket material. This ensures a perfect seal between two joining pipes.