• The majority of ships' pipes are made of mild steel.
• Flow rate, viscosity and pressure of fluid being carried
determine a pipe's diameter.
• Pipes in areas of a ship where there is a risk of gas explosion
are earthed because fluid flow can build up a static electricity
charge. Bonding strips are used across flanged joints to
maintain conductivity.
• Pipes that pass through other compartments pose potential
subdivision issues, especially open-ended pipes.
• Pipes, especially open-ended ones, compromise the integrity
of the compartments they pass through.
• The water circulating in cooling pipes will corrode them over
time.
• Pipes passing through tanks containing liquid are exposed to
corrosive attack on both surfaces.
• Pipes carrying liquefied gas seldom suffer internal corrosion.
• Visual checks of the external surfaces of a pipe will not indicate
its condition because it could be internally corroded and have
a reduced wall thickness.
• Most abrasive corrosion and consequent internal thinning
happens where the pipe bends and at elbows.
• Liquid flowing quickly will be turbulent as a result of fluid
separation and cavitation. Flow turbulence in a pipe will
cause pitting. A pipe with the correct diameter for the job
will eliminate turbulence.
• Pipes can be joined by butt-welding, with flange connections or
mechanical joints. However, the number of flange connections
allowed in the cargo pipes of a chemical tanker is strictly
controlled by classification society rules.
• Good pipe alignment during assembly of a run prevents
'locked-in' stress.
• The use of expansion (mechanical) joints, such as dresser-type
joints, is restricted to locations where pipes move because of
thermal expansion or contraction, or ship bending. Classification
society rules prohibit their use for the connection of cargo piping
in chemical tankers. The most common expansion joints are
compression couplings or slip-on joints.
• A pressure test of 1.5 times design pressure is a strength test;
a test at the design pressure is a tightness test. Pressure testing
can show the small cracks and holes that will not be found by a
visual examination.
• Pipes are held in place by supports or clips that prevent
movement from shock loads and vibration. Pipe failure is
common when pipes are allowed to vibrate.
• Pipes carrying flammable liquids have as few joints as possible
and these are shielded to prevent leaks from coming into
contact with hot surfaces.
• Mechanical joints are not normally fitted on pipes carrying
flammable liquids.
