If the tubing is to be run through a bulkhead, instead of being
connected through the bulkhead by a fitting, take extra care so that
the tubing is not scratched. For added protection in this operation,
the edges of the cutout must be taped before the line is installed.
TUBE REPAIR
A large percent of minor damage to aircraft plumbing is a result of
careless maintenance practices.
A misplaced foot or tool can
scratch, nick, or dent the tubing beyond tolerances.
Therefore,
caution on the part of maintenance personnel can prevent a great deal
of work.
When a damaged tube is discovered, the ideal solution is to replace
the complete section of tubing. In some instances, however, this may
not be possible.
In these cases minor damages can usually be
repaired, providing the damages are within specified limits.
Minor
repair techniques are described in the paragraphs that follow.
Dents.
Any dent less than 20 percent of tubing diameter is not
objectionable unless it is on the heel of a short bend radius in
which case the tubing is discarded.
Dents exceeding 20 percent of
tube diameter must be replaced.
Burnishing is not allowed in the
heel of bends where material has already been stretched thin during
forming.
Nicks. A nick in a piece of tubing subjects the tubing to failure
because of stress concentration caused by vibrations at the point of
the nick.
Nicks weaken tubing against internal pressure, and such
nicks must be burnished out to reduce a notch effect.
A nick no
deeper than 15 percent of wall thickness of aluminum, aluminum alloy,
copper, or steel tubing may be reworked by burnishing with hand
tools.
Any aluminum alloy, copper, or steel tubing with nicks in
excess of 15 percent of its wall thickness should be rejected.
Tubing which is nicked in a bend should be replaced if it is carrying
over 100 psi pressure.
For tubing carrying pressure of 100 psi or
less, a nick no deeper than 20 percent of wall thickness of aluminum,
aluminum alloy, copper, or steel may be reworked by burnishing with
Splicing.
When tube damages exceed the tolerances for repair
described in the preceding paragraphs and when it is not possible to
replace the entire section of tubing, a splice can be installed.
There are two different methods of splicing damaged tubing: one for
repairing low-pressure tubing, the other for repairing high-pressure
tubing. The steps involved in
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