2 Renewal Criteria

2.1 Local corrosion

2.1.1 Renewal thickness of local structural elements

Local structural elements include local supporting members and primary supporting members.

Steel renewal is required if the measured thickness, t_m in mm, is less than the renewal thickness, t_ren defined as:

t_ren = t_{as – built}– t_c – t_{vol_add}

2.1.2 Renewed area

Areas which need to be renewed based on the renewal criteria in [2.1.1] are, in general, to be repaired with inserted material which is to have the same or greater grade and yield stress as the original, and to have a thickness, t_repair in mm, not less than:

t_repair = t_{as – built} – t_{vol_add}

2.1.3 Alternative solutions

Alternative solutions may be adopted in accordance with the requirements of the Rules and/or documents of the individual Society which incorporate IACS UR Z10.2, Z10.4 and Z10.5, where the measured thickness, t_m is such as:

t_ren ≤ t_m < t_ren + t_res

2.2 Global corrosion

2.2.1 Application

The ship’s longitudinal strength is to be evaluated by using the thickness of structural members measured, renewed and reinforced, as appropriate, during special surveys, for ships over 10 years of age.

2.2.2 Renewal criteria

The hull girder strength criteria are given as detailed below.

Deck and bottom zones: The current hull girder section modulus at deck and at bottom determined with the thickness measurements are not to be less than 90% of the section modulus calculated according to Ch 5, Sec 1 with the gross offered thickness. Alternatively, the current sectional areas of the bottom zone and of the deck zone which are the sum of the measured item areas of the considered zones are not to be less than 90% of the sectional area of the corresponding zones determined with the gross offered thickness.
Neutral axis zone: The current sectional area of the neutral axis zone, which is the sum of the measured plating areas of this zone, is not to be less than the sectional area of the neutral axis zone calculated with the gross offered thickness minus 0.5 t_c.

If the actual reduction of the gross offered thickness of all items, of a given transverse section, which contribute to the hull girder strength is less than 10% for the deck and bottom zones and 0.5t_c for the neutral axis zone, the hull girder strength criteria of this transverse section is satisfied and the calculations of the different zone areas with measured thicknesses need not be carried out.

The gross offered thickness is defined in Ch 3, Sec 2.