Pipes and Bends – An Essential Guide for Second Engineers – Part 3

In our last article Pipes and Bends – An Essential Guide for Second Engineers – Part 2 we discussed about bends, elbows and miter bends.  In this article we will discuss about different types of pipe fittings found on ships.

Pipe Fittings

Pipe fittings are special parts that are used for joining two pipes together, to join a different size pipe to the existing piping, to regulate flow of fluid, etc.

Different types of pipe fittings are nipples, coupling, adapter, plugs, elbows, tees, valves etc. All the fittings are discussed below.


A nipple is basically a pipe with male threads on each side to facilitate joining two pipes or fittings with similar female threads.

It is made by cutting threads on both sides of a pipe by die or a suitable process. The nipples may be short or long.

Long Pipe Nipple

A long pipe nipple is similar to a standard nipple but longer in length.

It is used when there is more distance between the fittings or when a fitting like a valve is to be put at a distance.

Hexagonal Nipple

A hexagonal nipple is a pipe connector with male threads on both sides and a hexagonal nut in between for easy installation and screwing.

Both sides are to be screwed in pipe or fitting having reciprocating female threads.

Hexagonal Reducer Nipple

A hexagonal reducer nipple is a hexagonal shaped nipple with two different sizes of threads on each side.

The purpose of the hexagonal reducer nipple is to connect the pipes of two different sizes together

Hexagonal Long Nipple

A hexagonal long nipple is used where the distance between the pipe and the fittings is to be joined.

They are otherwise similar to the hexagonal nipples apart from the length.

Close Nipple

A close nipple is completely threaded and there is no unthreaded area.

This means that there is no hexagonal nut of plain pipe for putting the wrench. These can be damaged by using wrenches. Therefore, a special tool called nipple wrench, which holds the nipple from inside, is used for fitting.


A pipe coupling is a connector with female threads on both sides that allows two pipes or fittings with male threads to join together.

Coupling can be a normal pipe coupling or a hexagonal coupling. Pipe couplings are fittings that help to extend or terminate pipes.

Reducing Coupling

A reducer coupling is a coupling with two different sizes of threads on each side.

They also can be plain reducer coupling and hexagonal reducer coupling. They are used to connect two different sizes of pipes or fittings and sometimes also for flow control.


Pipe adapters are fittings that have to adapt to changes and are therefore used for joining different types of pipes such as a pipe to a hose. Adapters are used to extend or terminate the piping. They are also used to connect dissimilar pipes.

There are male to female adapters, parallel to taper thread adapters, and pipe to hose adapters etc.  Pipe adapters have a male or female thread on one side and an opposite gender thread on the other side.

Reducing Adapter

A reducing adapter is used for joining a pipe to a hose or tube as well as to help in flow control.

In doing so it controls the pressure acting on the hose at the end. It is used in applications where a copper tube is joined to the main steam pipe for trace heating.

These are the main types of pipe fittings. However, there are many more types. In the next article we shall continue discussing about various pipe fittings.

If you have not read the first part of this series, read it here – Pipes and Bends – An Essential Guide for Second Engineers – Part 1 

You may also like to read – What Is Quick Coupling or Quick Connect Coupler?

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About Author

Chief Engineer Mohit Sanguri is a Marine Chief Engineer (Class I Unlimited Power). He has 12 years of experience as Marine Engineer. He is currently working with Dynacom Tankers Ltd on their Bulk Carriers division and has served in the past with Wallems Ship Mgmt on Car Carriers and PCTC’s, MSC Ship Mgmt on Containers, Univan Ship Mgmt on RoRo’s and Five Stars Shipping on Bulkers and SNP Ship Mgmt on General Cargo at various designations.

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