Figure 15-3 shows a variety of common fittings.
copper and the second number is the percentage of
For example, the return bend shown in view A has the
nickel. Therefore, copper tubing with a 70-30
centers of the openings as close together as possible; the
composition is actually 70 percent copper and 30
elbow shown in view H makes a 90 bend; and the
percent nickel. Some copper-nickel tubing may be used
with Navy brazed tube fittings and butt-welded fittings.
elbow shown in view D makes a 45 bend. This variety
However, some types are not suitable for welding, while
in the design of fittings allows you to select' the
other types are not suitable for threading. The 70-30
appropriate fittings for any system.
composition has been used for some time in shipboard
Some of the plugs, caps, bushings, and nipples used
piping systems and heat exchangers. The Naval Sea
in shipboard piping systems are shown in figure 15-4.
Systems Command has authorized the use of the
Plugs are used to close an opening in fittings or
equipment. Caps are used for either temporary or
permanent seals of pipe ends. One type of reducing
bushing is used to connect two pieces of pipe or tubing
PLASTIC as a piping material has not been used to
together when they have different diameters. Another
any great extent on naval ships. However, considerable
type is used to connect pipe or tubing to a piece of
interest has been shown in the Navy's present and future
machinery. Nipples are used for connections to
use of plastic piping for naval ships.
machinery and also in plumbing systems.
Of all the different types of plastic piping material
A shock-resistant piping nipple is used for root
commercially available, two groups have been
connections to machinery. This type of nipple has
investigated for shipboard use: (1) glass-reinforced
straight pipe threads instead of tapered pipe threads.
polyester, or epoxy, and (2) polyvinyl chloride (PVC).
Threaded root connections are used on all ships where
Of the two types, the polyvinyl chloride has the best
piping and equipment are furnished with threaded
all-around characteristics for shipboard use.
bosses. A boss on a piece of machinery is a thick-wall
socket that is part of the housing. The boss allows the
PVC plastic piping has a number of advantages. It
connecting of an external pipe or nipple to the piece of
has an excellent resistance to saltwater corrosion. It is
machinery. If existing bosses have tapered pipe
also lightweight, easy to install, and highly resistant to
threads, it may be possible to retap them for straight pipe
weathering. Some high grades of PVC pipe are highly
threads. Otherwise, it will be necessary to use a nipple
resistant to shock. As for disadvantages, PVC piping
with tapered threads. In this case, you must be careful
material gives off hydrogen chloride gas when it burns.
when fitting the nipple to ensure that the gasket is
It cannot be used for carrying high temperature fluids,
compressed correctly and that the tapered threads are
nor can it be used when surrounding temperatures are
tightly seated. However, you should avoid the use of
high. Due to these disadvantages, plastic piping is not
tapered thread nipples whenever possible.
currently used below decks on surface ships. However,
PVC plastic piping is currently used in the interim and
Union fittings, and valves that have union ends, are
installed washdown systems aboard naval ships. For
used in piping systems to simplify repairs or alterations
more information on plastic piping, refer to NAVSHIPS
(fig. 15-5). The number of fittings and valves should
be kept to a minimum and checked periodically for
Unions are available in bronze, iron, and steel, and
are designed to withstand a wide range of temperatures
Every shipboard piping system includes a variety
and pressures. Bronze unions come in sizes up to 2 l/2
of fittings made from a number of different metals and
inches. Iron and steel unions (galvanized or black)
alloys. They are available in the same size range as the
come in sizes up to 3 inches. The straight, branch
pipe and tubing used in the systems. The layout and the
elbow, and run types of bronze unions are capable of
function of a system will determine the composition and
withstanding 250 psi pressure. The union bulkhead
the number of fittings used. The use of fittings is held
fitting is designed for 3000 psi water, oil, or gas lines
to a minimum because each fitting is a possible source
that pass through bulkheads.
for leaks. However, some fittings are necessary in any
piping system. Those normally used in shipboard
piping systems are described in this section.