expansion and contraction, the tremendous stresses in
repairs. Some of the valves are throttle valves and
the steam systems will cause failures.
valves that operate either automatically or
semi-automatically, such as safety, relief, regulating,
Expansion joints used on board ship include slip
and governing valves. Use pipe bends to keep the
joints and various corrugated and bellows-type joints.
number of joints down to a minimum.
Slip joints of the type shown in figure 15-28 are
used for some low-pressure piping. A slip joint consists
of a stuffing box, a packing gland, a male sliding tube,
Expansion joints must be kept in effective working
a female receptacle tube, and stop bolts that prevent
condition. Indicators are often fitted on expansion
separation of the male and female sections of the joint.
joints to show whether or not the joint is functioning
The stuffing box and the male tube are flanged so that
properly. Where such indicators are not fitted, a
the assembly can be connected to the piping. The
comparison of measurements taken on an expansion
packing in the stuffing box is compressed by studs and
joint before and after the system has reached its
nuts. The compression of the packing prevents leakage
operating temperature will indicate clearly whether or
at the joint as the pipe moves in and out for a limited
not the expansion joint is working properly.
Expansion joint bodies must be mounted securely
Slip-type expansion joints were once commonly
so that the movement is confined only to the part that is
used in shipboard steam piping systems. These joints
supposed to move.
are suitable only for low pressures, however, and the
increasingly high steam pressures on naval ships has led
The expansion joint is absolutely necessary for
to the use of other types of expansion joints in most
high-temperature steam systems. Metal expands when
steam systems. Slip-type expansion joints are still
heated and contracts when cooled. Steam lines are no
being used on many naval ships for steam escape piping
exception. Unless steps are taken to allow for
Figure 15-28.--Slip-type expansion joint.