Figure 16-18.--Flatness limits graph.
rejectable. If any pipe bend is rejected for any of the
previously mentioned reasons, the pipe should be
Pipe threading is a precise machining operation.
discarded and a new section of pipe bent.
Perfect threads are possible only if the threading dies
are in good condition and properly used. Even with a
perfectly cut thread, you will not get a sufficiently tight
ASSEMBLY AND DISASSEMBLY
joint unless every step is done properly.
Sometimes a leaking threaded joint can be
tightened with a reasonable amount of pull-up. If it
A great many joints are used in shipboard piping
cannot, you will have to take the joint apart, clean it,
systems. When standard fittings are used, such as
correct any bad thread conditions, recoat it with a
couplings, elbows, and T-joints, threads must be cut on
suitable thread compound, and then reassemble it.
pipes and tubing. Pipe threads cause frequent failures
When you do this, be careful to avoid new damage to
and it is often difficult to remove threaded joints. For
this reason, welded or brazed connections fitted with
When you cut the pipe to the required length, there
flanges or unions are used whenever possible. However,
you will find threaded fittings used in flexible piping,
will be a burr on the inside. This will be true whether
in low-pressure systems, and with pipe of 2 inches IPS
you use a cutting torch, a saw, or a pipe cutter. You will
or less. Actually, a joint capable of withstanding 1000
have to remove this burr with a file or a pipe reamer.
psi can be made if perfect threads are cut and if the joint
(For more information on threading and reaming pipe,
is properly assembled.
refer to chapter 5 of this manual.)