Corrugated and bellows-type expansion joints (fig.
15-29) are used for both medium- and high-pressure
Loops, U-shaped bends, and offsets are fitted into
piping systems aboard ship. These joints are used to
piping systems so that the expansion or contraction will
allow both axial and radial movement of main steam
be absorbed by the bending in the pipe that forms the
piping where it passes through the bulkhead.
bend. Because expansion bends are more reliable and
Corrugated and bellows-type expansion joints are
normally less expensive than expansion joints, they are
made of various materials, including hard rubber,
preferred when conditions permit their use. Figure
copper, nickel, and stainless steel. The accordion-like
15-30 shows a common type of expansion loop.
action of the corrugation or of the bellows allows the
Expansion bends and joints can be flexed in both
system to expand or contract. The movement of the
directions from their normal position. They should be
pipe is absorbed by the changing curvature of the
installed so that they are stressed in one direction when
corrugations or of the bellows.
the piping is cold, and stressed in the other direction
when the piping is hot. The amount and direction of the
prestress or cold pull-up to be applied to piping and
expansion bends or joints is indicated on the appropriate
ship's plans. These instructions must be followed
carefully to prevent failure of the expansion joints,
piping, and connected equipment.
COLD SPRING JOINTS
Another method used to provide for expansion in
high-pressure piping is the cold spring joint. The pipe
for this joint is cut short an amount usually equal to one
half the computed expansion. After the system is
fabricated and ready for installation, a dutchman (an
accurately machined blank flange), equal in thickness
to the required amount of cold spring, is inserted
between the flanges of the cold spring joint. When all
other connections have been made, the dutchman is
removed and the joint set up to about 40,000 psi with
temporary pull-up bolts. The temporary bolts are then
replaced one by one with permanent installation bolts
set up to the required bolt stress.
WELDED AND BRAZED JOINTS
The majority of joints found in subassemblies of
piping systems are welded joints, especially in
high-pressure piping. The welding is done according to
standard specifications that define the materials and
Figure 15-29.--Corrugated and bellows-type expansion joints.
Figure 15-30.--Expansion loop.