Expanding and reducing flanges are used to increase or decrease the bore size of a pipeline. Expander and reducer flanges are a good alternative to buttweld reducers when the required pipeline bore reduction or increase is small (one or two sizes). For larger size changes, the use of buttweld fittings is recommended.
EXPANDING FLANGE (“EXPANDER”)
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).
The drawing of an ASME expanding flange.
REDUCING FLANGE (“REDUCER”)
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.