A flange is a method of connecting pipes, valves, pumps and other equipment to form a piping system. It also provides easy access for cleaning, inspection or modification. Flanges are usually welded or screwed. Flanged joints are made by bolting together two flanges with a gasket between them to provide a seal. The most commonly used flanges are weld neck flange, slip-onflange, blind flange, socket weld flange, threaded flange, and lap joint flange (RTJ Flange). Metal flanges are classified from 150 to 2500 # rating. In addition to these standard flanges, some special ones exist, called Weldoflange/Nipoflange and Elboflange, swivel flange, expander/reducer flange, and orifice flanges. They are also being classified further based on the type of face of the flanges – like flat face (FF), Raised Face (RF), ring joint (RTJ), lap joint, male and female (M&F), tongue and groove (T&G).