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Repairs, except those
of an emergency nature, should only be attempted when access to the
defective area is such as to provide adequate access for welding and
inspection.
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The welders employed
for the repairs are to be experienced and qualified to carry out this
type of work. Whenever possible, the component should be removed from
the ship and the repairs carried out in a properly equipped workshop
under controlled conditions.
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Complete removal of
all defective material is essential for a successful repair. However,
the material removed should be the minimum consistent with this and
the excavation should be shaped so as to allow good access for welding.
The complete removal of all defective material is to be verified by
magnetic particle examination before welding is commenced.
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The chemical composition
should be established by reference to the appropriate certificate
and the reported analysis compared with the limits given in the Rules
for Materials. If the quoted composition is not within these limits,
special consideration must be given to the welding procedure.
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Where certificates are
not available, the chemical composition should be determined by the
analysis of representative drillings. In assessing these results,
allowance should be made for heterogeneous effects, and provided the
carbon content does not exceed 0,26 per cent, special consideration
of the welding procedure is not necessary.
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Welding consumables
should be of an approved low hydrogen type depositing weld metal with
mechanical properties similar to that of the forging or casting. The
use of grade 3H or 3YH consumables is recommended.
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Due to the relatively
large mass and the consequent chilling effect, it is recommended that
in all cases an adequate area around the repair should be pre-heated
to about 100°C. This pre-heat should be maintained until the repair
is completed. Pre-heating temperature in excess of 100°C may be
required.Due to the relatively large mass and the consequent chilling
effect, it is recommended that in all cases an adequate area around
the repair should be pre-heated to about 100°C. This pre-heat
should be maintained until the repair is completed. Pre-heating temperature
in excess of 100°C may be required.
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As far as is practicable,
all welding should be done in the downhand position. Manual or automatic
processes may be used as appropriate.
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The surplus weld metal
should be removed by machining or grinding and the surface of the
repair area smoothed to a satisfactory profile. The area should then
be checked for freedom from cracks and other defects by magnetic particle
examination. Where extensive repairs have been carried out, ultrasonic
examination may also be requested at the discretion of the Surveyors.
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A stress-relieving treatment
is to be carried out after completion of the repairs. A suitable temperature
range is 600 to 650°C with a soaking period of one hour per 25
mm thickness of the repaired section.
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Rudder stocks should
be treated in a furnace properly equipped with means for temperature
measurement and control. In general, the furnace should be large enough
to take the entire rudder stock. Post-weld heat treatment may be localised.
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Sternframes should be
stress-relieved by heat treatment preferably using electric heating
elements, and cooling should be retarded by a thermal blanket.
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After heat treatment
and final machining or grinding has been completed, the repaired area
should be re-examined by a magnetic particle method.
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Where the repairs have
been carried out satisfactorily in compliance with the above, they
should be recorded in the memoranda. If repairs are considered to
be of a temporary nature, a Condition of Class should be recommended.
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When reinforcement of
sternframes is necessary, care should be taken to maintain continuity
with the ends of the reinforcement well-tapered to obviate hard spots.