A plate flange is a circular, flat disc that is welded to the end of a pipe to allow the flange to be fastened to another pipe. The terms flat flange, plain flange, flange slip, etc. are frequently used to describe it. It is common to practice in fuel and water pipelines to bolt together two Plate Flanges with a gasket in the middle.

When building a pipeline, the length of the pipes is not always known. In order to unite two pipes that might not be completely matched, the plates can also be welded with a minor bias toward the shaft.

A serrated finish on the inner mating surface of plate flanges enables the plate to fit inside the gasket material. Regardless of the materials used to make them, plate flange designs are uniform in any given dimension. In doing so, it guarantees a perfect fit between a 6-inch (15-cm) black pipe flange and a 6-inch stainless steel flange. The two connecting pipes will be completely sealed as a result.

The most common applications for plate flanges are in water and fuel pipelines, where two flange plates are bolted together with a gasket in the middle. The flange plate will be used to make junctions, tees, and joints and will have bolt holes all the way around it.