Everyone knows about the effect of corrosion on a ship's hull, but
few people consider the effect of corrosion on piping. Pipes pose
a hidden danger, a danger that is often forgotten about.
Pipes are silent workers, conveying fluid or allowing air to enter
or to leave a space, and are the means by which many control
systems operate. They are unnoticed until pipe failure occurs and
a machine stops operating, a space floods or oil is spilled. Pipes
penetrate almost every enclosed space, as well as the shell both
above and below the waterline, and the weather deck. There is no
system on a ship that has such enormous potential to cause fire,
pollution, flooding or even total loss.
The majority of ships' pipes are constructed of ferrous material,
a material that is attacked by all forms of corrosion. As a ship
ages, so does the piping system. Maintenance is not always easy,
because pipes, unlike the hull, are difficult to examine because
of their numbers and inaccessibility. It is practically impossible
to maintain them internally, where most corrosion takes place,
and at times just as difficult to maintain a pipe's external surface.
As a result, pipes can receive minimum maintenance, and pipe
failure is often the result. As an operator once remarked when
asked, "When is it necessary to replace a pipe?", "When it bursts."
The purpose of this guide is to alert ships' crews to the danger of
catastrophic loss that can result from pipe failure. Our intention is
to raise awareness of the limit of redundancy in pipe design and
the difficulties involved in the surveying of ships' piping. Pipe
failure will only be prevented by a proactive approach to
inspection, maintenance and repair.
Failed pipes cause, or contribute to, many serious claims.
• Bagged grain on a small bulk carrier was damaged after water
escaped from an air pipe running between a ballast tank and
the cargo hold. The pipe had a corrosion crack where it
connected to the tank top and water escaped through the crack
when the ballast tank was overfilled. The ship was 18 years
old, but nothing had ever been done to protect the pipe from
corrosion; not even a lick of paint. Cost – $120,000. Repairs to
the pipe would have cost less than $50.
• Bulk fertiliser was damaged when water escaped from a
topside ballast tank via a sounding pipe that passed through
the tank into the hold below. The pipe was cracked and holed
inside the ballast tank which contained saltwater ballast and
water drained from the tank into the hold. Cost – $380,000.
Damaged sounding pipes are easily identified during
inspections and repairs are inexpensive.
• A cargo ship foundered and four crewmen lost their lives,
when a seawater-cooling pipe in the engine room burst and the
engine had to be stopped. The ship was blown onto a lee shore
where it broke up on the rocks. Cost – four lives and $1m.
Corroded seawater pipes connecting directly to the shell are
often wrongly repaired with a doubler. Doublers should not
normally be used to repair shell plating.
• A product tanker was gravity ballasting into a segregated tank.
The ballast line passed through a cargo tank. When ballast
stopped flowing, a corrosion hole in the line allowed oil to
escape into the sea through an open valve. Cost – $975,000.
• The main engine of a bulk carrier was seriously damaged when
alumina in the cargo hold got into its fuel tank. There was a
hole in the air pipe that passed through the cargo hold into the
tank. Cost – $850,000. The pipe had never been properly
examined during surveys.
• A diesel alternator caught fire after a low-pressure fuel oil pipe
burst and sprayed oil onto the exhaust manifold. The pipe had
been vibrating, and this movement had caused the pipe's wall
to chafe and become thin. The claim cost a new alternator and
$100,000, but the fitting of a pipe support would have cost a
mere $2!
