4.2 Areas under consideration
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1330 – Guidelines for Maintenance and Repair of Protective Coatings – (11 June 2009) - Annex – Guidelines for Maintenance and Repair of Protective Coatings - 4 Coating Conditions - 4.2 Areas under consideration

4.2 Areas under consideration

Parent topic: 4 Coating Conditions

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 ratingfootnote.

  4.2.1.2 Special attention should be given to coating in critical structural areas which are definedfootnote 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).

  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).

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).

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).

Double bottom tanks

 Areas of tank boundaries and attached structure, in lower and upper half of tank (two areas to consider).

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).

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).

After peak tanks

 Areas of tank boundaries and attached structure in upper and lower (two areas to consider).

  Notes:

  • 1 Each area includes plating and attached structural members.

  • 2 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.

  • 3 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 Areas under consideration (vertical)
h ≤ 15 m Two areas (lower/upper)
h > 15 m Three areas (lower/middle/upper)

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.

4.3 In-service condition monitoring

  4.3.1 It is recommended that all ballast tanks, especially for ships over six years of age, are inspected at least annually by the crew.

  4.3.2 Standardized reports should be used with the following information, where applicable:

  • .1 ship's name;

  • .2 tank number;

  • .3 inspection date;

  • .4 inspection by whom;

  • .5 year coated;

  • .6 coating name/type;

  • .7 last repaired;

  • .8 surface area;

  • .9 coating condition (GOOD, FAIR or POOR);

  • .10 Pitting corrosion – Yes/No;

  • .11 amount of rust scale (in m2 or % of areas under consideration);

  • .12 access arrangement condition;

  • .13 sounding pipe condition;

  • .14 vent pipe condition;

  • .15 ballast pipes condition;

  • .16 structural damage, mechanical damage, location and extent; and

  • .17 other comments.

  4.3.3 The coating condition rating is used to give an objective report of the condition so that the urgency of the repairs can be established and the most cost effective solution found. The suitable rating system for this purpose is GOOD/FAIR/POOR as specified in section 4.1. A copy of the latest standardized report should be maintained on board for use of the owner.

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