Reducers & Coupling

 1) REDUCERS:

When the piping engineer wants to reduce the diameter of a straight run of pipe, a reducing fitting must be used. It is classified as two types

• Concentric Reducer
• Eccentric Reducer

i) Concentric Reducer :

It has a common centerline. It maintains the same centerline at both the large and small ends of fittings. Using this reducer in a piperack would not permit the small diameter end of the pipe run to rest on a pipe support.

ii) Eccentric Reducer :

It has offset centerlines. When the outside surface of the pipelines (for  E.g. either the top of pipes or bottom of the pipes ) are to be maintained same, then eccentric reducers are used. It is used in pipe rack to maintain a constant bottom of pipe (BOP). Because pipe supports within a pipe rack are of same elevation, a pipe must have a consistent bottom of pipe elevation so it can rest on each support throught its entire length.

No matter the size of reducer, it always drawn as a double line symbol. The large end is always listed first, no matter the flow direction and flat side must be indicated.

2) Coupling:

Used primarily for connecting small bore screwed and socket weld pipe to large bore pipe headers, the coupling is also used extensively where instrument connections are needed. There are two methods used to make branch connection with couplings:

• The coupling rests on the external surface of the pipe header and is welded from the outside.
• A hole is bored into the pipe header large enough to accept the OD of the coupling. The coupling is inserted into the hole and is then welded.