4.2 Areas under consideration
4.2.1 General
4.2.1.1 Recognizing that different areas in the tank experience different coating breakdown and corrosion patterns, the intent of this section is to subdivide the planar boundaries of the tank for evaluation of coating into areas small enough to be readily examined and evaluated by the surveyor.
However, the areas subdivided should not be so small as to be structurally insignificant or too numerous to practically report on. Coating condition in each area should be reported using current
practice and terminology (frame numbers, longitudinal numbers and/or strakes numbers, etc.). Each
area is then rated "GOOD","FAIR" or "POOR" and the tank rating should not be higher than the rating of its "area under consideration" having the lowest rating**.
4.2.1.2 Special attention should be given to coating in critical structural areas which are defined*** as "locations which have been identified from calculations to require monitoring as indicated in the Coating Technical File (CTF) from new building stage or from the service history of the subject ship or from similar or sister ships (if available) to be sensitive to cracking, buckling or corrosion which would impair the structural integrity of the ship". Each critical structural area is rated GOOD","FAIR" or "POOR", applying table 1 and the rating of each "area under consideration"should then not be higher than the rating of its critical structural area (if present) having the lowest rating.
4.2.1.3 The "area under consideration" with the worst coating condition should determine the frequency of surveys, such as those addressed in resolution A.744(18) for tankers. Hence, it is not
intended to "average" the coating condition for all "areas under consideration" within a tank, to determine an "average" coating condition for the entire tank.
4.2.2 Ballast tanks in oil tankers
Definitions of "areas under consideration" for ballast tanks in oil tankers are as follows (also illustrated for a wing ballast tank, a fore peak ballast and aft peak tank in figures 1, 2 and 3 below, respectively).
Single-hull tanker - wing ballast tanks
Deck and bottom
Areas of deck and bottom plating with attached structure (one area to consider for deck and one area to consider for bottom).
Side shell and longitudinal bulkheads
Areas of side shell and longitudinal bulkheads with attached structure, in lower, middle and upper third (three areas to consider for side shell and three areas to consider for longitudinal bulkhead).
Transverse bulkheads (forward and aft)
Areas of transverse bulkhead and attached stiffeners, in lower, middle and upper third (three areas to consider for forward transverse bulkhead and three areas to consider for aft transverse bulkhead).
Double-hull tanker
Double bottom ballast tank
Areas of tank boundaries and attached structure, in lower and upper half of tank (two areas to consider).
Double-hull side tank
Deck and bottom
Areas of deck and bottom plating with attached structure (one area to consider for deck and one area
to consider for bottom).
Side shell and longitudinal bulkheads
Areas of side shell and longitudinal bulkheads with attached structure, in lower, middle and upper third (three areas to consider for side shell and three areas to consider for longitudinal bulkhead).
Transverse bulkheads (forward and aft)
Areas of transverse bulkhead and attached stiffeners, in lower, middle and upper third (three areas to consider for forward transverse bulkhead and three areas to consider for aft transverse bulkhead).
Figure 1 - "Areas under consideration" indicated for a wing ballast tank, from one side, i.e. deck, side shell, longitudinal bulkhead and transverse bulkheads
Figure 2 - "Areas under consideration" indicated for a fore peak ballast tank
Fore peak tanks
Areas of tank boundaries and attached structure, in upper, middle and lower third of tank (three areas to consider).
After peak tanks
Areas of tank boundaries and attached structure, in lower and upper half of tank (two areas to consider).
Figure 3 - "Areas under consideration" indicated for an aft peak tank
4.2.3 Ballast tanks in ships other than oil tankers
Definitions of "areas under consideration" for ballast tanks and double-side skin spaces in ships other than oil tankers, which are based on representative tank configuration, are as follows (also illustrated for topside tanks, hopper tanks, double bottom tanks, side tanks, fore peak tanks and after peak tanks in figures 4 to 9 below, respectively):
Topside tanks
Deck, vertical strake and bottom
Areas of deck, vertical strake and bottom plating with attached structure (one area to consider for deck and vertical strake with attached structure and one area to consider for bottom).
Side shell
Side shell with attached structure, in lower and upper or in lower, middle and upper depending on the vertical height (two areas to consider for side shell, but if the vertical height is more than 15 m, three areas to consider).
Transverse bulkheads (forward and aft)
Areas of transverse bulkhead and attached stiffeners, in lower and upper or in lower, middle and upper depending on the vertical height (two areas to consider for forward transverse bulkhead and aft transverse bulkhead, but if the vertical height is more than 15 m, three areas to consider).
Figure 4 - Topside tanks
Hopper tanks
Hopper, side girder and bottom
Areas of hopper, side girder and bottom plating with attached structure (one area to consider for bottom and side girder with attached structure and one area to consider for hopper).
Side shell
Side shell, including bilge plating, with attached structure, in lower and upper or in lower, middle and upper depending on the vertical height (two areas to consider for side shell, but if the vertical height is more than 15 m, three areas to consider).
Transverse bulkheads (forward and aft)
Areas of transverse bulkhead and attached stiffeners, in lower and upper or in lower, middle and upper depending on the vertical height (two areas to consider for forward transverse bulkhead and aft transverse bulkhead, but if the vertical height is more than 15 m, three areas to consider).
Figure 5 - Hopper tanks
Double bottom tanks
Areas of tank boundaries and attached structure, in lower and upper half of tank (two areas to consider).
Figure 6 - Double bottom tanks
Side tanks
Deck and bottom
Areas of deck and bottom plating with attached structure (one area to consider for deck and one area to consider for bottom).
Side shell and longitudinal bulkheads
Side shell and longitudinal bulkheads with attached structure, in lower and upper or in lower, middle and upper depending on the vertical height (two areas to consider for side shell, but if the vertical height is more than 15 m, three areas to consider).
Transverse bulkheads (forward and aft)
Areas of transverse bulkhead and attached stiffeners, in lower and upper or in lower, middle and upper depending on the vertical height (two areas to consider for forward transverse bulkhead and aft transverse bulkhead, but if the vertical height is more than 15 m, three areas to consider).
Figure 7 - Side tanks
Fore peak tanks
Areas of tank boundaries and attached structure in upper and lower or upper, middle and lower depending on the vertical height (two areas to consider for fore peak tanks, but if the vertical height is more than 15 m, three areas to consider).
Figure 8 - Fore peak tanks
After peak tanks
Areas of tank boundaries and attached structure in upper and lower (two areas to consider).
Figure 9 - After peak tanks
Notes:
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Each area includes plating and attached structural members.
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A tank configuration which is combined with two or more tanks may be dealt with in separate in accordance with its unit shape of tank configuration, e.g., a tank which has a combination figure of a hopper tank and a double bottom tank or a tank which is combined with a wing tank, a side tank and a hopper tank.
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For fore peak tank or after peak tank, which consists of ballast tank and void space, they should be separately considered. It is important to note that void spaces are not considered under these Guidelines.
If the vertical height of ballast tanks other than double bottom tanks, fore peak tank, and after peak tank is more than 15 m, it should be divided into three areas under consideration as shown in table 1.
Table 1
Maximum vertical height (h) of tank
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Areas under consideration (vertical)
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h = 15 m
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Two areas (lower/upper)
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h > 15 m
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Three areas (lower/middle/upper)
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When deciding the boundary between lower/(middle)/upper parts for areas under consideration of the vertical surface, other than dividing the vertical surface equally by the number of areas decided according to table 1, the conspicuous structural member(s) such as stringers and/or horizontal girders on bulkheads or side shell may be the boundary, which should be mentioned in the report.
** Examples of how to report coating conditions with respect to areas under consideration are given in appendix 10 of IACS Recommendation 87.
*** Refer to appendix 5 of IACS Recommendation 87.