Reducers are applied in piping systems, in order to have the pipe diameter differ from one end to the next. The two ends have unequal diameters to achieve this purpose. Most of the time the upstream diameter is larger than the downstream size. Of course the same fitting can be used in reverse as an expander / increaser.


There are 2 types of standard reducers available: concentric and eccentric reducers. The concentric one, which resembles a cone, is used to join pipe sections on the same axis.
The eccentric type has an edge which is parallel to that of the connecting pipe, which allows it to align with one side of the inlet. So the outlet is off center to the inlet.

Properties / use of Reducers

The length of a reducer is relatively short, which implies the transition in flow is abrupt. A designer can opt to use more reducers for a smoother flow. So instead of 1 reducer 10”x 5” (which is 178 mm) multiple reducers can be applied: 10”x 8” + 8”x 6” + 6”x 5” , with a total length of 470mm.

By using a common concentric reducer, the transition of a medium will run gradually. Concentric reducers are usually applied in vertical pipelines, and prove to be very useful in services where cavitation is present.

The dissimilar eccentric type has specific characteristics. It will prevent noise and vibration, and has proven ideal to combine diameters with radically different sizes. Also it requires less installation space. To prevent cavitation in horizontal liquid lines, these reducers are applied top flat*. But horizontal eccentric reducers will be applied bottom flat*, in order for condensed fluid or oil to be allowed to drain at low points.

*When drawing an eccentric reducer, piping designers use the abbreviation “TF” or “BF” which stands for “top flat” and “bottom flat”.


Arcus provides a wide range of butt weld reducers in various stainless steel grades. We have them available from stock in welded and seamless execution, in EN and ASTM both from Asian and European manufacturers.

How to specify an enquiry or order

1: Quantity
2: Type: Concentric / Eccentric
3: Execution: seamless or welded
4: Standard: ASME / DIN / JIS etc.
5: Sizes: upstream and downstream size
6: Wall thickness
7: Height: Distance from end to end
8: Material type and grade

Example: 10 pieces Seamless Concentric reducer acc. to ASME A/SA 403, 3” x 2” STD Height; 76mm, 316L

Auteur: Daniel Hage

+31 (0) 78 648 3648

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