Reducers used in Piping Industry

Reducers used in Piping Industry: A short literature

Pipelines are not of uniform size and there is requirement of reducing or expanding the lines depending on process requirement or availability of material. Here comes the importance of a special pipe fitting called Reducers.

Reducers are most extensively used in piping industry to reduce or expand the straight part of run pipe. Basically, reducers are available in two styles:

  • Concentric reducers and
  • Eccentric reducers.

Concentric Reducers:

As shown in Fig. 1. In this type of reducers area reduction is concentric and center line of the pipe on bigger end and smaller end  remains same.  These styles are normally used for vertical lines.

Concentric Reducers
Fig.1: Concentric Reducers


Eccentric Reducers:

As shown in Fig. 2 , in this style of reducer there is an offset in between the center lines of bigger end and center line of smaller end. This offset or eccentricity will maintain a flat side either on top or on bottom side.

Eccentric reducer
Fig.2: Eccentric Reducer


This offset or eccentricity can easily be found out by the following equation:

Eccentricity=(Bigger end ID-Smaller end ID)/2

While using this type of reducer the user has the option of orienting the flat side. Usually for horizontal lines, eccentric reducers are oriented with either the flat side up or down and the same with deviation is mentioned in isometric.

Normally eccentric reducers with flat side down are preferred for following cases on horizontal lines:
• On Sleepers and Piperacks
• On lines requiring gravity flow
• On pump suction line which handle slurry.

Eccentric reducers with flat side up are used for all pump suction lines (excluding pumps handling slurry) on horizontal lines. This way one can avoid air getting trapped inside the pipeline during initial venting through pump casing and will help in avoiding Cavitation.

Depending on end connections of this fitting with straight pipe, reducers are grouped as follows:

Butt Welding reducers:  The applicable pressure rating, dimensional and material standards for butt welding reducers are same as those applicable to butt welding elbows.

Socket welding reducers: As shown in Fig.3. such reducers are available in concentric type only &  in the form of a coupling with one end socket to fit larger diameter pipe and other end socket to fit smaller diameter pipe.  Standards are same as those applicable to socket welding elbows.

Socket Welded Reducers
Fig.3: Socket Welded Reducers

Screwed reducers: Available only in concentric type and are in the form of coupling having one end to fit bigger pipe and other end to fit smaller pipe.  ASME B16.11 is applicable dimensional standard. Material standards including pressure ratings are same as of screwed elbows.

Flanged reducers: Their pressure rating, use, material and dimensional standards are same as those applicable
to flanged elbows. Regardless of reduction their face to face dimensions are governed by the larger pipe size.

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3 thoughts on “Reducers used in Piping Industry: A short literature”

  1. Thanks for the very good article.

    I wanted to know about the basic difference between Swage nipple and Reducers.

  2. Thanks for the article

    In addition, it must say that standard ASME B16.9 used for butt welding reducers and B16.11 for forged steel, socket welding and threaded ones.
    In selection of the materials, reducers and other components must made of material having at least the similar allowance stress of the pipe and must have a pressure retention strength of at least 87.5% of the wall thickness of the matching piping.


  3. Furthermore, when the reducer size dropped less that 2″, it will be called Swage nipple and it is covered by MSS SP 95. connections are socket welding and threaded.

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