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 TB 55-1900-201-45/1
be an indication of structural weakness and need for structural modification or reinforcement, in addition to repair. In riv-
eted construction, loosening and failure of the riveting within the double bottom may be observed. It is apparent that
once the fastenings begin to fail, the stress levels and corrosion rates in adjoining structure increase rapidly. The practi-
cal solution to this problem is the early detection of the failing fastenings and the timely and adequate replacement of
these fastenings in order that the existing material in the vessel can be made to perform to its capacity. The old adage
that "a stitch in time saves nine" is certainly applicable
here.
E-20. Side Plating. In the side plating the strake "between wind and water" is an area which is highly susceptible to cor-
rosion. The maximum general wastage is to be expected in this area. Also, serious localized corrosion may often be
encountered in way of overboard discharges and scupper openings. The latter may usually be repaired by the use of
insert plates rather than by plate renewals. Suitably attached wastage doublers may be used on sound plating as a
means of protection.
E-21. Longitudinal and Transverse Bulkheads. Cargo hold bulkheads are usually not troubled by excessive corrosion
except along the lower boundaries and in way of bilge wells. Such corrosion is a local condition and should be repaired
by the use of insert plates or well attached lapped plates if sufficient material remains for proper installation. In the case
of the longitudinal and transverse bulkheads in a tank ship, especially where light products have been carried, corrosion
is to be expected. Wastage up to about 35 percent may be accepted provided there is no evidence of deformation when
subjected to a hydrostatic test. The top strake of bulkhead plating in a tank ship is usually made heavier in anticipation of
the increased corrosion to be expected in this area which is usually wet but not submerged. Therefore, when referred to
the original scantling, an increased allowance for deterioration may be permitted. Applying a 35 percent wastage to the
original scantling of the next to topmost strake will serve to establish the minimum thickness acceptable in the topmost
strake.
E-22. Frames, Beams and Stiffeners. Generally the flanges and portions of the webs next to the flanges are more
highly stressed, more subject to mechanical damage and corrode faster than the balance of the member. If excessive
wastage has occurred but is limited to the flange and outer portion of the web, cropping of the defective section rather
than complete renewal may be permitted. Details on this are included in Section IV. The use of short lengths of flat bar
welded in way of deteriorated material is not an acceptable repair. Full Length flat bar doublers may be satisfactory in
some cases but this represents a change in design so the installation should be made in accordance with an approved
plan. Notwithstanding the above, flat bar doublers are never acceptable on internals within the tanks of a tank ship be-
cause of the danger of gas entrapment. Often times, projecting frames or beams are deformed due to hook pulls, dam-
age by
E-13
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