Section 2 Materials

2.1 General

2.1.1 The Rules relate in general to the construction of steel ships, although consideration will be given to the use of other materials.

2.1.2 Materials used in the construction of the ship are to be manufactured and tested in accordance with the requirements of theRules for the Manufacture, Testing and Certification of Materials, July 2022 (hereinafter referred to as the Rules for Materials.

2.1.3 Materials for which provision is not made therein or covered by this Section may be accepted, provided that they comply with an approved specification and such tests as may be considered necessary.

2.2 Grade of steel

2.2.1 The grade of steel, supply condition and its mechanical properties are to be indicated on the construction plans.

2.2.2 In order to distinguish between the material grade requirements for different hull members at varying locations along the ship, material classes are assigned, as shown in Table 6.2.1 Material classes and grades. For each class, depending on thickness, the material grade requirements are not to be lower than those given in Table 6.2.2 Steel grades for normal operation.

Table 6.2.1 Material classes and grades

Structural member category		Material class/Minimum grade
SECONDARY
A1.	Longitudinal bulkhead strakes, other than belonging to the Primary category	Class I within 0,4L _R amidships
A2.	Deck plating exposed to weather, other than that belonging to the Primary or Special category	Grade A/AH outside 0,4L _R amidships
A3.	Side plating
PRIMARY
B1.	Bottom plating, including keel plate
B2.	Strength deck plating, excluding that belonging to the Special category	Class II within 0,4L _R amidships
B3.	Continuous longitudinal plating of strength members above strength deck	Grade A/AH outside 0,4L _R amidships
B4.	Uppermost strake in longitudinal bulkhead
SPECIAL
C1.	Sheerstrake (or rounded gunwale) and stringer plate at strength deck, see Note 1	Class III within 0,4L _R amidships
C2.	Deck strake at longitudinal bulkhead, see Note 1	Class II outside 0,4L _R amidships
		Class I outside 0,6L _R amidships
C3.	Strength deck plating at corners of large hatch openings	Class III within 0,6L _R amidships
	Strength deck plating at corners of large hatch openings	Class II outside 0,6L _R amidships
C4.	Bilge strake in ships with double bottom over the full breadth and length less than 150 m	Class II within 0,6L _R amidships
		Class I outside 0,6L _R amidships
C5.	Bilge strake in other ships, see Note 1	Class III within 0,6L _R amidships
		Class II outside 0,4L _R amidships
		Class I outside 0,6L _R amidships
ADDITIONAL MINIMUM REQUIREMENTS FOR SINGLE STRENGTH DECK SHIPS OF LENGTH GREATER THAN 150 m
D1.	Longitudinal plating of strength deck where contributing to the longitudinal strength	Grade B/AH within 0,4L _R amidships
D2.	Continuous longitudinal strength plating of members above strength deck
D3.	Single side strakes for ships without inner continuous longitudinal bulkhead(s) between bottom and strength deck
ADDITIONAL MINIMUM REQUIREMENTS FOR SHIPS OF LENGTH GREATER THAN 250 m
E1.	Sheerstrake (or rounded gunwale) and stringer plate at strength deck, see Note 1	Grade E/EH within 0,4L _R amidships
E2.	Bilge strake, see Note 1	Grade D/DH within 0,4L _R amidships
Note 1. Single strakes required to be of Class III or of Grade E/EH and within 0,4L _R amidships are to have breadths not less than 800 + 5L _R mm, but need not be greater than 1800 mm, unless limited by the geometry of the ship’s design. Note 2. For strength members not mentioned, Grade A/AH may be generally used. Note 3. Steel grade is to correspond to the as-fitted thickness. Note 4. Plating materials for sternframes supporting the rudder and propeller boss, rudders, rudder horns and shaft brackets are, in general, not to be of lower grades than corresponding to Class II. For rudder and rudder body plates subjected to stress concentrations (e.g. in way of lower support of semispade rudders or at upper part of spade rudders) Class III is to be applied. Note 5. RAS seating and support structure are to be of Grade D/DH for t ≤ 20 mm and Grade E/EH for t > 20 mm. For ships operating in cold weather RAS seating and support structure are to be of Grade E/EH. Note 6. Corner inserts in way of complex openings such as for lifts and side doors which may impinge on the deck plating or stringer plate are to be of Grade D/DH for t ≤ 20 mm and Grade E/EH for t > 20 mm. Note 7. The material class used for reinforcement and the quality of material (i.e. whether mild or higher tensile steel) used for welded attachments, such as waterway bars and bilge keels, is to be similar to that of the hull envelope plating in way. Where attachments are made to rounded gunwale plates, special consideration will be given to the required grade of steel, taking account of the intended structural arrangements and attachment details. Note 8. The material class for deck plating, sheerstrake and upper strake of longitudinal bulkhead within 0,4L _R amidships is also to be applied at structural breaks of the superstructure, irrespective of position. Note 9. Engine seat top plates outside 0,6L _R amidships may be Grade A/AH. Steel grade requirement for top plates within 0,6L _R amidships will be specially considered.

Table 6.2.2 Steel grades for normal operation

Thickness, in mm	Material Class
	I		II		III
	Mild steel	H.T. steel	Mild steel	H.T. steel	Mild steel	H.T. steel
≤10	A	AH	A	AH	A	AH
10-15	A	AH	A	AH	A	AH
15-20	A	AH	A	AH	B	AH
20-25	A	AH	B	AH	D	DH
25-30	A	AH	D	DH	D	DH
30-35	B	AH	D	DH	E	EH
35-40	B	AH	D	DH	E	EH
40-45	D	DH	E	EH	E	EH
45-50	D	DH	E	EH	E	EH

2.2.3 The material class and minimum grade requirements specified in Table 6.2.1 Material classes and grades and Table 6.2.2 Steel grades for normal operation for normal operation are applicable for normal service, which assumes navigation to areas where the lowest mean daily average air temperature is not less than -10°C

2.2.4 The material grade of the exposed structure of ships intended to operate in external air temperatures below -10°C, including all ships designed for sea area SA1, is to be in accordance with Vol 1, Pt 6, Ch 6, 2.4 Ships operating in cold weather conditions.

2.2.5 Ships operating in certain environmental conditions, and those where operational requirements may lead to a risk of impact damage, or ships with military notations, may require higher toughness grades.

2.2.6 Where a ship has the notations FDA, ESA or RSA, the toughness requirements for steel will be specially considered on the basis of fatigue crack limitation and subsequent propagation through the structure.

2.2.7 Where tee or cruciform connections employ full penetration welds and the plate material, is subject to significant strains in a direction perpendicular to the rolled surfaces, it is recommended that consideration be given to the use of special plate material with specified through thickness properties, and tested in accordance with Ch 3, 8 Plates with specified through thickness properties of the Rules for Materials. The plan should indicate the material grade followed by the letter Z (e.g. DZ, DHZ).

2.3 Refrigerated spaces

2.3.1 Where the minimum design temperature of the steel falls below 0°C in refrigerated spaces, the grade of steel for the following items is to comply, in general, with the requirements of Table 6.2.3 Grades of steel for refrigerated spaces with a minimum design temperature below 0 Degrees C:

Deck plating.
Webs of deck girders.
Longitudinal bulkhead strakes attached to deck.

Table 6.2.3 Grades of steel for refrigerated spaces with a minimum design temperature below 0 Degrees C

Minimum design temperature, in ^oC	Thickness, in mm	Grades of steel
0 to -10	t ≤12,5	B/AH
	12,5 < t ≤ 25,5	D/DH
	t > 25,5	E/EH
< –10 to –25	t ≤ 12,5	D/DH
	t > 12,5	E/EH
< –25 to –40	t ≤ 12,5	E/EH
	t > 12,5	FH/LT-FH (see also Ch 3, 6 Carbon–manganese and nickel alloy steels for low temperature service)

2.3.2 Unless a temperature gradient calculation is carried out to assess the design temperature in the items defined in Vol 1, Pt 6, Ch 6, 2.3 Refrigerated spaces 2.3.1, the temperature to which the steel deck may be subjected is to be assessed as shown in Table 6.2.4 Assessment of deck temperature

Table 6.2.4 Assessment of deck temperature

Arrangement	Deck temperature
(1) Deck not covered with insulation in the refrigerated space	Temperature of the refrigerated space
(2) Deck covered with insulation in the refrigerated space and not insulated on the other side	Temperature of the space on the uninsulated side
(3) Deck covered with insulation on both sides (a) Temperature difference not greater than 11^oC (b) Temperature difference greater than 11^oC but not greater than 33^oC (c) Temperature difference greater than 33^oC	Mean of the temperatures of the spaces above and below the deck Mean of the temperatures of the spaces above and below the deck less 3^oC Deck temperature will be specially assessed
Note Where one of the internal spaces concerned is not refrigerated, the temperature of the space is to be taken as 5^oC.

2.4 Ships operating in cold weather conditions

2.4.1 For ships intended to operate in areas with external air temperatures below -10°C MDAT, e.g. regular operations during winter seasons to Arctic or Antarctic waters, the material grade requirements of structures above the Cold Waterline are not to be of lower grades than those given in Table 6.2.5 Material classes and grades for structures exposed to low temperatures , Table 6.2.6 Materials for Class I for low air temperatures, Table 6.2.7 Materials for Class II for low air temperatures and Table 6.2.8 Materials for Class III for low air temperatures for the specified design air temperature.

2.4.2 The specified design air temperature is to be selected by the Owner based on the lowest mean daily average temperature (MDAT) for the area and period of operations considered in the Concept of Operations.

where

Mean	=	statistical mean over a minimum of 20 years
Average	=	average during one day and one night
Lowest	=	lowest during the year
MDHT	=	Mean Daily High Temperature
MDAT	=	Mean Daily Average Temperature
MDLT	=	Mean Daily Low Temperature

Note The MDLT is used as the reference baseline for the Rules for the Winterisation of Ships, July 2022 and IMO Polar Code, and is typically taken as 3°C lower than the MDAT.

Figure 6.2.1 Design air temperature shows the definition graphically.

Figure 6.2.1 Design air temperature

2.4.3 Unless otherwise specified, all ships designed for sea area SA1 are to be designed for a lowest mean daily average design air temperature of –30°C MDAT or lower. However, where agreed, materials for SA1 ships not intended for operations in cold weather conditions may be based on requirements for normal service for higher design air temperatures (-10°C MDAT or higher).

2.4.4 Where the material class in Table 6.2.1 Material classes and grades is higher than in Table 6.2.5 Material classes and grades for structures exposed to low temperatures , the higher material class is to be applied.

2.4.5 For ships where the optional Winterisation H notation is applied, see Rules for the Winterisation of Ships, July 2022, note that the external design air temperature defined in the Rules for the Winterisation of Ships, July 2022 is taken as 13°C lower than the design air temperature, i.e. if the design air temperature is -12°C MDAT, then the external design air temperature for the application of the Rules for the Winterisation of Ships, July 2022 is -25°C (-12°C MDAT minus 13°C).

2.4.6 For ships where a Polar Service Temperature (PST) is to be assigned, note that the PST is taken as 13°C lower than the design air temperature, i.e. if the design air temperature is -12°C MDAT, then the PST for the application of the Polar Code is -25°C (-12°C MDAT minus 13°C).

Table 6.2.5 Material classes and grades for structures exposed to low temperatures

Structural member category		Material class
SECONDARY
A1.	Deck plating exposed to weather, other than that belonging to the Primary or Special category	Class I
A2.	Side plating above the Cold Waterline (CWL), see Note 4
A3.	Transverse bulkheads above CWL, see Note 4
PRIMARY
B1.	Strength deck plating, excluding that belonging to the Special category, see Note 1	Class II within 0,4L _R amidships
B2.	Continuous longitudinal members above strength deck	Class I outside 0,4L _R amidships
B3.	Longitudinal bulkhead above CWL, see Note 4
SPECIAL
C1.	Sheerstrake (or rounded gunwale) and stringer plate at strength deck, see Note 2	Class III within 0,4L _R amidships
C2.	Deck strake at longitudinal bulkhead, see Note 3	Class II outside 0,4L _R amidships
Note 1 Plating at the corners of deck openings, superstructure ends and other structural discontinuity is to be specially considered. The requirements of Class III are to be applied in positions where high local stresses may occur but the material is not to be less than Grade E/EH. Note 2 Not to be less than Grade E/EH within 0,4LR amidships in ships with length exceeding 250 m. Note 3 In ships with breadth exceeding 70 m at least three deck strakes are to be Class III. Note 4 The Cold Waterline (CWL) is to be taken as 0,3 m below the minimum design Ballast Waterline (BWL).

Table 6.2.6 Materials for Class I for low air temperatures

Thickness, in mm	Design air temperature
	-11°C to -15°C		-16°C to -25°C		-26°C to -35°C		-36°C to -45°C		-46°C to -55°C
	MS	HT	MS	HT	MS	HT	MS	HT	MS	HT
≤10	A	AH	A	AH	B	AH	D	DH	D	DH
10-15	A	AH	B	AH	D	DH	D	DH	D	DH
15-20	A	AH	B	AH	D	DH	D	DH	E	EH
20-25	B	AH	D	DH	D	DH	D	DH	E	EH
25-30	B	AH	D	DH	D	DH	E	EH	E	EH
30-35	D	DH	D	DH	D	DH	E	EH	E	EH
35-45	D	DH	D	DH	E	EH	E	EH	-	FH
45-50	D	DH	E	EH	E	EH	-	FH	-	FH
Note . MS and HT are defined as Mild Steel and High Tensile Steel respectively.

Table 6.2.7 Materials for Class II for low air temperatures

Thickness, in mm	Design air temperature
	-11°C to -15°C		-16°C to -25°C		-26°C to -35°C		-36°C to -45°C		-46°C to -55°C
	MS	HT	MS	HT	MS	HT	MS	HT	MS	HT
≤10	A	AH	B	AH	D	DH	D	DH	E	EH
10-20	B	AH	D	DH	D	DH	E	EH	E	EH
20-30	D	DH	D	DH	E	EH	E	EH	-	FH
30-40	D	DH	E	EH	E	EH	-	FH	-	FH
40-45	E	EH	E	EH	-	FH	-	FH	-	FH
45-50	E	EH	E	EH	-	FH	-	FH	-	FH
Note . MS and HT are defined as Mild Steel and High Tensile Steel respectively.

Table 6.2.8 Materials for Class III for low air temperatures

Thickness, in mm	Design air temperature
	-11°C to -15°C		-16°C to -25°C		-26°C to -35°C		-36°C to -45°C		-46°C to -55°C
	MS	HT	MS	HT	MS	HT	MS	HT	MS	HT
≤10	B	AH	D	DH	D	DH	E	EH	E	EH
10-20	D	DH	D	DH	E	EH	E	EH	-	FH
20-25	D	DH	E	EH	E	EH	E	EH	-	FH
25-30	D	DH	E	EH	E	EH	-	FH	-	FH
30-35	E	EH	E	EH	-	FH	-	FH	-	FH
35-40	E	EH	E	EH	-	FH	-	FH	-	FH
40-50	E	EH	-	FH	-	FH	-	FH	-	FH
Note . MS and HT are defined as Mild Steel and High Tensile Steel respectively.

2.4.7 All bulwarks, spurn-waters, unlagged gas turbine intake structures, side screens, tie down points, etc. are to be constructed of steel of equivalent toughness to that of the material to which they are attached.

2.4.8 Steel grades for rudder horn and stem (including the adjacent strake of shell plating), are given in Table 6.2.9 Steel grades for rudder horn, shaft brackets and stem for ships intended to navigate in Arctic or Antarctic conditions The steel grades of internal members attached to these items are to be of the same grade (or equivalent) with due account taken of difference in thickness.

2.4.9 For non-exposed structures and structures below the Cold Waterline, the material grades are not to be lower than those given in Table 6.2.1 Material classes and grades.

2.4.10 Structure attached to and within a distance of 2,0 m within unheated spaces and 0,75 m for heated spaces of the exposed boundary plating is to be of the same material grade as that of the exposed plating, but the grade may be adjusted depending on the material thickness of the attached structure.

Table 6.2.9 Steel grades for rudder horn, shaft brackets and stem for ships intended to navigate in Arctic or Antarctic conditions

Item	Condition	Construction	Steel grade⁽²⁾⁽³⁾
			f < 25(1)	f ≥ 25(1)
Rudder horn	Fully immersed	Cast steel	Carbon manganese steel Grade 400	Carbon manganese steel Grade 400
		Fabricated	Grade EH	Grade EH
	Periodically immersed or exposed	Cast steel	Carbon manganese steel Grade 460	2 1/4 Ni steel or equivalent
		Fabricated	Grade FH	1 1/2 Ni steel or equivalent
Shaft brackets	Fully immersed	Cast steel	Special Grade	Special Grade
		Fabricated	Class B/AH	Class B/AH
	Periodically immersed or exposed	Cast steel	Carbon manganese steel Grade 400	Carbon manganese steel Grade 460
		Fabricated	Class II	Grade FH
Stem including adjacent strake of shell plating	Fully immersed	Fabricated	Class B/AH	Class B/AH
		Cast steel	Carbon manganese steel Grade 400	Carbon manganese steel Grade 400
	Periodically immersed or exposed	Fabricated	Class II	Class II
		Cast steel	2 1/4 Ni steel	2 1/4 Ni steel
Rudder stock		Forged	see Ch 5, 2.4 Mechanical tests of the Rules for Materials
		Cast steel	Carbon manganese steel grade 400
Note 1. f = Note where P _o is the maximum propulsion shaft power, in kW, for which the machinery is classed Δ is displacement, in tonnes, at Ice Load Waterline or Deepest Ice Operation Waterline when floating in water of relative density of 1,0. Note 2. For cast steel, see Ch 4, 7 Ferritic steel castings for low temperature service of Rules for Materials. The requirements for carbon manganese steel grades 400 and 460 are to include the additional compositional requirements for Special grade in accordance withCh 4, 2.2 Chemical composition of the Rules for Materials. Note 3. For C–Mn LT60 and Ni plates, see Ch 3, 6 Carbon–manganese and nickel alloy steels for low temperature service of Rules for Materials. Note 4. For Special grade, see Ch 4, 2.2 Chemical composition of the Rules for Materials.

2.5 Mechanical properties for design

2.5.1 The scantlings determined within this Part of the Rules assume that mild steel has the following mechanical properties:

	N/mm²
Yield strength (minimum)	235
Tensile strength	400–490
Modulus of elasticity	200 x 10³

2.5.2 Steels having a minimum yield stress not less than 265 N/mm² are regarded as higher tensile steels.

2.5.3 Factors for structural assessment are given in Vol 1, Pt 6, Ch 5 Structural Design Factors

2.5.4 For the application of the requirements of Vol 1, Pt 6, Ch 6, 2.5 Mechanical properties for design 2.5.3 special consideration will be given to steel where σ _o ≥ 390 N/mm². Where such steel grades are used in areas which are subject to fatigue loading the structural details are to be verified using fatigue design assessment methods.