8 Acceptance criteria

  8.1.1 For ships built under the IACS Common Structural Rules, the acceptance criteria shall be according to the IACS Common Structural Rules^footnote, as applicable, and as specified in sections 8.2, 8.3 and 8.4.

  8.1.2 For ships not built under the IACS Common Structural Rules, the acceptance criteria shall be according to the requirements of the classification society depending on the ship's age and structural elements concerned.

  8.2.1 Side structures

8.2.1.1 If the pitting intensity in an area where coating is required, according to the IACS Common Structural Rules^footnote, as applicable, is higher than 15% (see figure 1), thickness measurements shall be performed to check the extent of pitting corrosion. The 15% is based on pitting or grooving on only one side of a plate.

8.2.1.2 In cases where the pitting intensity is exceeding 15%, as defined above, an area of 300 mm diameter or more, at the most pitted part of the plate, shall be cleaned to bare metal and the thickness measured in way of the five deepest pits within the cleaned area. The least thickness measured in way of any of these pits shall be taken as the thickness to be recorded.

8.2.1.3 The minimum remaining thickness in pits, grooves or other local areas shall be greater than 70% of the as-built thickness, in the side shell, hopper tank and topside tank plating attached to the each side frame, over a width up to 30 mm from each side of it, without being greater than the renewal thickness (t_ren).

  8.2.2 Other structures

8.2.2.1 For plates with a pitting intensity less than 20%, see figure 1 above, the measured thickness, t_m, of any individual measurement shall meet the lesser of the following criteria:

• t_m ≥ 0.7 (t_as-built - t_{vol add}) (mm); and

• t_m ≥ t_ren - 1 (mm),

• where:

  • t_as-built thickness of the structural member, in mm; tvol add

  • t_{vol add} voluntary thickness addition; thickness, in mm, voluntarily added as the owner's extra margin for corrosion wastage in addition to t_C;

  • t_ren renewal thickness; minimum allowable thickness, in mm, below which renewal of structural members shall be carried out;

  • t_C total corrosion addition, in mm, defined in IACS CSR^footnote, as applicable; and

  • t_m measured thickness, in mm, on one item, i.e. average thickness on one item using the various measurements taken on this same item during periodical surveys of ships in service.

8.2.2.2 The average thickness across any cross section of the plating shall not be less than the renewal criteria for general corrosion given in the IACS Common Structural Rules^footnote, as applicable.

  8.3.1 Provided that the overall corroded height of the edge corrosion of the flange, or web in the case of flat bar stiffeners, is less than 25%, see figure 2 above, of the stiffener flange breadth or web height, as applicable, the measured thickness, t_m, shall meet the lesser of the following criteria:

• t_m ≥ 0.7 (t_as-built - t_{vol add}) (mm); and

• t_m ≥ t_ren - 1 (mm),

  8.3.2 The average measured thickness across the breadth or height of the stiffener shall not be less than that defined in the IACS Common Structural Rules^footnote, as applicable.

 8.3.3 Plate edges at openings for manholes, lightening holes, etc. may be below the minimum thickness given in the IACS Common Structural Rules^footnote, as applicable, provided that:

• .1 the maximum extent of the reduced plate thickness, from the opening edge, below the minimum, shall not be more than 20% of the smallest dimension of the opening and shall not exceed 100 mm; and

• .2 rough or uneven edges may be cropped-back provided that the maximum dimension of the opening shall not be increased by more than 10% and the remaining thickness of the new edge shall not be less than t_ren - 1 mm.

  8.4.1 Where the groove breadth is a maximum of 15% of the web height, but not more than 30 mm, see figure 3 above, the measured thickness, t_m, in the grooved area shall meet the lesser of the following criteria:

• t_m ≥ 0.75 (t_as-built - t_{vol add}) (mm);

• t_m ≥ t_ren - 0.5 (mm), and

• t_m ≥ 6 mm.

  8.4.2 Structural members with areas of grooving greater than those in paragraph 8.4.1 above shall be assessed based on the criteria for general corrosion as defined in the IACS Common Structural Rules^footnote, as applicable, using the average measured thickness across the plating/stiffener.