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What Is a Loose Flange?

By Lori Kilchermann
Updated May 17, 2024
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A loose flange is a device that is welded onto the end of a piece of pipe to create half of a flanged coupling. Consisting of a flat steel forging with bolt holes around the perimeter and an opening in the center the size of the pipe that is intended to be welded onto the loose flange, the component can be made of carbon steel or stainless steel to meet the intended application. There are loose flange types to fit elbows, valves and nearly every type of pipeline component in use.

Due to the nature of pipelines, the connections and couplings can rarely be constructed in advance. The use of a loose flange allows a worker to create a coupling in any location along the pipeline that is feasible. The worker simply cuts the pipe at the required location and places a loose flange onto the end of the pipe. After carefully preparing the pipe to weld, the loose flange is welded permanently to the end of the pipe. If a valve or elbow is required, the worker simply welds the flange onto the elbow or valve as well as the pipe, and the union is made.

Many elbows, valves and other such pieces are created with a flange cast onto the component. In this case, the pipe is prepared to join the piece by welding the flange onto the end of the pipe only. The flange aligns with the already cast flange and the union is made. On some components, however, there is no flange precast into the component and a flange must be welded onto the component to complete the union. This application calls for a loose flange to be used in the construction of the pipeline. The welding and fitment typically must be completed by a licensed and certified welder who has been tested to make certain that all of the welds will be up to code.

In many cases, a pipeline is built using straight pipe sections and loose flanges all welded together to form a completed line of pipe. Whether welded by man or machine, the pipeline is assembled from straight-cut ends of pipe being welded together to form virtually seamless pipe with flanged unions being installed at critical locations on the pipeline. In these locations, a loose flange is welded to the pipe on both sides of the union and the pipeline is bolted together using a gasket and many hardened bolts.

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