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Technical Library > FLANGES > INTRODUCTION TO FLANGES > Expanding and Reducing Flanges
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EXPANDING AND REDUCING FLANGES


Expanding and reducing flanges are a good alternative to butt weld reducers to reduce the pipeline bore of one or two measures. In this article, we define these types of forged products and list the other types of special flanges available on the market. 


 

WHAT MEANS EXPANDING AND REDUCING FLANGES?

Expanding and reducing flanges (otherwise called, expander/reducer flanges) are used to change the bore size of a pipeline. These special types of flanges substitute the use of butt weld fittings for small reductions of a pipeline flow capacity (max 1 or 2 sizes up or down). A butt weld concentric reducer is needed, instead, for greater bore size changes.

 

EXPANDING FLANGE (“EXPANDER”)

Special flanges: type expanding flange (or expander flange) to increase the bore of the pipeline

Expanding flanges, or “expander flanges”, are used to increase the bore of the pipeline from a specific point to another or to connect pipes to other mechanical devices such as pumps, compressors, and valves that have different inlets sizes. The expanding flange represented in the picture is a welding neck flange with a larger bore on the non-flanged end.

Expanding flanges can be used to increase the run pipe bore only by one or maximum two sizes and not more (example: from 2 to 3 or maximum 4 inches). Expander flanges are cheaper (and lighter) solution to using a combination of a butt weld reducer and a standard flange (which is the standard solution for pipe bore increases above 2 sizes). The most common materials for expanding flanges are A105 (high-temp. carbon steel), A350 (LTCS) and ASTM A182 (stainless steel and above). Pressure ratings and dimensions of expanding flanges are in accordance with the ANSI/ASME B16.5 specification and are available with raised or flat face (RF/FF).

expanding flange dwg

The drawing of an ASME expanding flange.

 

REDUCING FLANGE (“REDUCER”)

Special flange: reducing flange (or reducer flange) to decrease the size of the pipeline bore

Reducing flanges, otherwise called reducer flanges, have an opposite function than expander flanges seen above, i.e. they are used to decrease the bore of a pipeline. The bore of the run pipe can be safely reduced by only 1 or 2 sizes (otherwise a solution based on the combination of a butt weld reducer and a standard flange has to be used). Reducing flanges are available in most sizes and material grades, and are not generally available from stock. Reducing flanges follow the same considerations in terms of specifications, sizes and material grades as expander flanges.

 

OTHER TYPES OF SPECIAL FLANGES

Other types of special flanges are:

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