1 General

1.1 Applicability

1.1.1 The corrosion additions given in these Rules are applicable to carbon-manganese steels, stainless steels, stainless clad steels and aluminium alloys. Corrosion addition for the exposed carbon steel side of stainless clad structure is to be as required in Table 1 for the corresponding compartment.

The corrosion additions for other materials are to be in accordance with the requirements of the Society.

1.2 Corrosion addition determination

1.2.1 The corrosion addition for each of the two sides of a structural member, t_c1 or t_c2, is specified in Table 1.

The total corrosion addition, t_c, in mm, for both sides of the structural member is obtained by the following formula:

t_c = Roundup_0.5 (t_c1 + t_c2) + t_res

For an internal member within a given compartment, the total corrosion addition, t_c is obtained from the following formula:

t_c = Roundup_0.5 (2t_c1) + t_res

where t_c1 is the value specified in Table 1 for one side exposure to that compartment.

Roundup_0.5 (t) means that t is rounded to the upper half millimetre.

The total corrosion addition, t_c, in mm, for compartment boundaries and internal members made from stainless steel, or aluminium is to be taken as:

t_c = t_res= 0.5

In case of stainless clad steel, the corrosion additions, t_c1, for the carbon steel side and t_c2, for the stainless steel side are respectively to be taken as:

t_c1 as specified for the corresponding compartment in Table 1
t_c2 = 0

Table 1 : Corrosion addition for one side of a structural member

Compartment type	Structural member		**t_c1 or t_c2**
			Oil tankers	BC-A or BC-B ships with L ≥ 150 m	Other BC ships
Ballast water tank, bilge tank, drain storage tank, chain locker ⁽¹⁾	Face plate of PSM	Within 3m below top of tank ⁽⁴⁾	2.0
		Elsewhere	1.5
	Other members ^{(2) (3)}	Within 3m below top of tank ⁽⁴⁾	1.7
		Elsewhere	1.2
Cargo oil tank, slop tank	Face plate of PSM	Within 3m below top of tank ⁽⁴⁾	1.7	N/A
		Elsewhere	1.4
	Inner-bottom plating/bottom of tank		2.1
	Other members	Within 3m below top of tank ⁽⁴⁾	1.7
		Elsewhere	1.0
Dry bulk cargo hold ⁽⁵⁾	Transverse bulkhead	Upper part ⁽⁶⁾	N/A	2.4	1.0
		Lower stool: sloping plate, vertical plate and top plate ⁽⁷⁾		5.2	2.6
		Other parts		3.0	1.5
	Sloped plating of hopper tank, inner bottom plating			3.7	2.4
	Other members	Upper part ⁽⁶⁾		1.8	1.0
		Webs and flanges of the upper end brackets of side frames of single side bulk carriers
		Webs and flanges of lower brackets of side frames of single side bulk carriers		2.2	1.2
		Other parts		2.0	1.2
Exposed to atmosphere	Weather deck plating		1.7
	Other members		1.0
Exposed to seawater	Shell plating between the minimum design ballast draught waterline and the scantling draught waterline		1.5
	Shell plating elsewhere		1.0
Fuel and lube oil tank			0.7
Fresh water tank			0.7
Void spaces ⁽⁸⁾	Spaces not normally accessed, e.g. access only via bolted manhole openings, pipe tunnels, inner surface of stool space not common with a dry bulk cargo hold or ballast cargo hold, etc.		0.7
Dry spaces	Internals of machinery spaces, pump room, store rooms, steering gear space, etc.		0.5
⁽¹⁾ 1.0 mm is to be added to the plate surface within 3m above the upper surface of the chain locker bottom.
⁽²⁾ 0.5 mm is to be added to the plate surface exposed to ballast for the plate boundary between water ballast and heated cargo oil tanks/slop tanks. 0.3mm is to be added to each surface of the web and face plate of a stiffener in a ballast tank and attached to the boundary between water ballast and heated cargo oil tanks or heated fuel/lube oil tanks/slop tanks. Heated oil tanks are defined as tanks/slop tanks arranged with any form of heating capability (the most common type is heating coils).
⁽³⁾ 0.7 mm is to be added to the plate surface exposed to ballast for the plate boundary between water ballast and heated fuel oil or lube oil tanks.
⁽⁴⁾ Only applicable to cargo tanks/slop tanks and ballast tanks with weather deck as the tank top. The 3 m distance is measured vertically from and parallel to the top of the tank.
⁽⁵⁾ Dry bulk cargo hold includes holds intended for the carriage of dry bulk cargoes, which may carry water ballast.
⁽⁶⁾ Upper part of the cargo holds correspond to an area above the connection between the topside and the inner hull or side shell. If there is no topside, the upper part corresponds to the upper one third of the cargo hold height (where a plane bulkhead is fitted in way of a dry bulk cargo hold, the upper part of the bulkhead is defined in the same manner).
⁽⁷⁾ If there is no lower stool fitted (i.e. engine room bulkhead or fore peak bulkhead) or if a plane bulkhead is fitted, then this corrosion addition should be applied up to a height level with the opposing bulkhead stool in that hold. In the case where a stool is not fitted on the opposing bulkhead, the vertical extent of this zone is to be from the inner bottom to a height level with the top of the adjacent hopper sloping plate, but need not be taken as more than 3 m.
⁽⁸⁾ For the determination of the corrosion addition of the outer shell plating, the pipe tunnel is considered as for a water ballast tank.

1.2.2 Minimum value of total corrosion addition

The total corrosion addition is not to be taken less than 2 mm except for web and face plate of stiffeners or in way of internals of dry spaces where 1.5 mm is applicable.

These minimum values of corrosion addition are not applicable to structural members made of stainless steels, stainless clad steels or aluminium alloys.

1.2.3 Stiffener

The corrosion addition of a stiffener is determined according to the location of its connection to the attached plating.

1.2.4 When a local structural member/plate is affected by more than one value of corrosion addition, the most onerous value is to be applied to the entire strake.