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 TB 55-1900-201-45/1
SECTION II. Corrosion Limits
2-2. General.
a. Without other weakening factors, a local thickness deterioration of up to 25% may be accepted before re-
placement is necessary. This is based in part on the condition usually found aboard ship that all structural members do
not deteriorate uniformly. This means that in the application of this percentage considerable judgment is called for de-
pendent upon the location and extent of wasted material. Localized wastage of some portions of plates or structural
members in excess of 25% may be accepted in some cases, if the condition of the adjacent material is sufficiently good
to maintain an adequate margin of strength. In these instances, careful attention should be given that a local deteriora-
tion does not result in a radical change in section or general weakening which could act as a notch. On the other hand,
there may be instances where either general or localized wastages of less than 25% would call for replacement of mate-
rial.
b. Deck Plating. Deck plating comprises a highly stressed portion of the hull girder and is of critical importance to
the longitudinal strength of the vessel. Accelerated corrosion may be expected in the deck plating because it is subject
to mechanical abuse, repeated scaling, exposure, and is frequently awash. Because of this, the deck plating, especially
in the midship's half length, should be carefully examined for cracks, leaks, or signs of excessive wear. The corners of
hatch or other deck openings, the corners of deck erections, pads, or other items producing interruptions or hard spots
should be examined for evidence of cracking. In the case of riveted construction, special attention should be paid to the
riveting of butts. Discovery of working or loose riveted butts calls for prompt corrective action. There may be evidence
of cracking at the rivet holes not yet sufficiently extensive to extend beyond the rivet head. Cracking of the plate will, in
general, call for replacement of the plating. Buckling of deck plating is uncommon; however, any such buckling can seri-
ously impair the strength of the vessel and calls for corrective action.
c. Deck Longitudinals. In tank vessels the deterioration of deck longitudinals may be more rapid than that of deck
plating. These longitudinals are necessary to support the deck plating so that it can carry local static loading, to provide
panel stiffness to the deck plating so that, as a part of the hull girder, it can carry compressive loading without buckling,
and also to directly contribute to the hull girder stiffness and strength. Because the relative importance of these factors
may be different when dealing with different designs, it is very difficult to lay down any specific wastage limits. How-
ever, for the usual proportion of longitudinals to plating and spans of a tank vessel, deterioration of some deck longitudi-
nals up to a maximum of 40% (or about 0.18" wastage, whichever is the lesser), may be accepted. However, the aver-
age deterioration may not be more than 30% (or about 0.14" wastage, whichever is the lesser). The above applies to
longitudinals fabricated from structural shapes such as
2-4
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