Using a loose flange allows a worker to create a coupling anywhere along the pipe that is feasible.
A loose flange is a device that is welded to the end of a piece of pipe to create one half of a flanged coupling. Consisting of flat forged steel with bolt holes around the perimeter and a pipe-size opening in the center that is intended to be welded to the loose flange, the component can be made from carbon steel or stainless steel to suit the intended application. There are loose flange types to fit elbows, valves, and almost every type of piping component in use.
Due to the nature of piping, connections and couplings can rarely be built in advance. Using a loose flange allows a worker to create a coupling anywhere along the pipe that is feasible. The worker simply cuts the pipe at the required location and attaches a loose flange to the end of the pipe. After carefully preparing the pipe for welding, the loose flange is permanently welded to the end of the pipe. If a valve or elbow is required, the operator simply welds the flange to the elbow or valve as well as the pipe and the joint is made.
Many elbows, valves, and other similar parts are created with a flange cast on the component. In this case, the tube is prepared to be joined to the part by welding the flange only at the end of the tube. The flange is aligned with the already cast flange and the joint is made. On some components, however, there is no prefabricated flange on the component and a flange must be welded to the component to complete the joint. This application requires the use of a loose flange in pipe construction. Normally, welding and installation should be done by a licensed and certified welder who has been tested to ensure all welds are up to code.
In many cases, a pipeline is constructed using straight pipe sections and loose flanges, all welded together to form a complete pipe line. Whether mechanically or manually welded, the duct is assembled from straight pipe ends that are welded together to form a virtually seamless pipe with flanged joints that are installed at critical locations in the duct. At these locations, a loose flange is welded to the pipe on both sides of the joint and the pipe is bolted together using a gasket and many hardened screws.