Section 1 Materials of construction

1.1 General

1.1.1 The Rules relate in general to the construction of steel units, although consideration will be given to the use of other materials. For the use of aluminium alloys, see Pt 4, Ch 2, 1.3 Aluminium.

1.1.2 The materials used in the construction of the unit are to be manufactured and tested in accordance with the requirements of the Rules for the Manufacture, Testing and Certification of Materials (hereinafter referred to as the Rules for Materials). Materials for which provision is not made therein may be accepted, provided that they comply with an approved specification and such tests as may be considered necessary, see also Pt 3, Ch 1, 4 Materials.

1.1.3 The requirements for materials for use in liquefied gas containment systems are specified in Pt 11 PRODUCTION, STORAGE AND OFFLOADING OF LIQUEFIED GASES IN BULK of these Rules.

1.1.4 For concrete structures, see Pt 9, Ch 4 Materials and Durability.

1.2 Steel

1.2.1 Steel having a specified minimum yield stress of 235 N/mm² (24 kgf/mm²) is regarded as mild steel. Steel having a higher specified minimum yield stress is regarded as higher tensile steel.

1.2.2 When higher tensile steel is used in the construction of the unit the local scantlings determined from the Rules for steel plating, longitudinals, stiffeners and girders, etc., may be based on a k factor determined as follows:

or 0,66, whichever is the greater

where

specified minimum yield stress, of the higher tensile steel in N/mm² (kgf/mm²).

1.2.3 When higher tensile steel is used in the primary structure of ship units, the determination of the hull girder section modulus is to be based on a higher tensile steel factor

kL determined in accordance with Pt 4, Ch 2, 1.2 Steel 1.2.3.

Table 2.1.1 Values of

Specified minimum yield stress In N/mm² (kgf/mm²)
235 (24)	1,0
265 (27)	0,92
315 (32)	0,78
355 (36)	0,72
390 (40)	0,66
460 (47)	0,62
NOTES
1. Intermediate values by linear interpolation.
2. For the purpose of calculating hull moment of inertia as specified in Pt 3, Ch 4, 5.8 Hull moment of inertia 5.8.1 of the Rules for Ships, =1,0.

1.2.4 For the application of the requirements of Pt 4, Ch 2, 1.2 Steel 1.2.2 and Pt 4, Ch 2, 1.2 Steel 1.2.3, special consideration will be given to steel where > 355 N/mm² (36 kgf/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.

1.2.5 Where steel castings or forgings are used for major structural components, they are to comply with Ch 4 Steel Castings or Ch 5 Steel Forgings of the Rules for Materials, as appropriate.

1.3 Aluminium

1.3.1 The use of aluminium alloy is permitted for superstructures, deckhouses, hatch covers, helicopter platforms, or other local components on board offshore units, except where stated otherwise in Pt 3, Ch 1, 4.5 Aluminium structure, fittings and paint.

1.3.2 Except where otherwise stated, equivalent scantlings are to be derived as follows:

Plating thickness:

Section modulus of stiffeners:

where

c	=	0,95 for high corrosion resistant alloy
c	=	1,0 for other alloys

thickness of aluminium plating

thickness of mild steel plating

section modulus of aluminium stiffener

section modulus of mild steel stiffener

0,2 per cent proof stress or 70 per cent of the ultimate strength of the material, whichever is the lesser.

1.3.3 In general, for welded structure, the maximum value of to be used in the scantlings derivation is that of the aluminium in the welded condition. However, consideration will be given to using unwelded values depending upon the weld line location, or other heat affected zones, in relation to the maximum applied stress on the member (e.g., extruded sections).

1.3.4 A comparison of the mechanical properties for selected welded and unwelded alloys is given in Pt 4, Ch 2, 1.3 Aluminium 1.3.6.

1.3.5 Where strain hardened grades (designated Hxxx) are used, adequate protection by coating is to be provided to avoid the risk of stress corrosion cracking.

1.3.6 The use of aluminium alloy for primary structure will be specially considered.

Table 2.1.2 Minimum mechanical properties for aluminium alloys

Alloy	Condition		0,2% proof stress, N/mm²		Ultimate tensile strength, N/mm²
Alloy	Condition		Unwelded	Welded (see Note 4)	Unwelded	Welded (see Note 4)
5083	O/H111		125	125	275	275
5083	H112		125	125	275	275
5083	H116/H321		215	125	305	275
5383	O/H111		145	145	290	290
5383	H116/H321		220	145	305	290
5086	O/H111		100	95	240	240
5086	H112		125 (see Note 2)	95	250 (see Note 2)	240
5086	H116/H321		195	95	275	240
5059	O/H111		160	160	330	330
5059	H116/H321		260	160	360	300
5456	O		125	125	285	285
5456	H116		200 (see Note 5)	125	290 (see Note 5)	285
5456	H321		215 (see Note 5)	125	305 (see Note 5)	285
5754	O/H111		80	80	190	190
6005A	T5/T6	Extruded: Open Profile	215	100	260	160
(see Note 1)		Extruded: Closed Profile	215	100	250	160
6061	T5/T6	Rolled	240	125	290	160
(see Note 1)		Extruded: Open Profile	240	125	260	160
		Extruded: Closed Profile	205	125	245	160
6082	T5/T6	Rolled	240	125	280	190
		Extruded: Open Profile	260	125	310	190
		Extruded: Closed Profile	240	125	290	190
NOTES
1. These alloys are not normally acceptable for application in direct contact with sea-water.
2. See also Ch 8, 1.5 Chemical composition 1.5.2 or Ch 8, 1.8 Mechanical tests 1.8.3 of the Rules for Materials.
3. The mechanical properties to be used to determine scantlings in other types and grades of aluminium alloy manufactured to National or proprietary standards and specifications are to be individually agreed with LR, see also Ch 8, 1.1 Scope 1.1.5 of the Rules for Materials.
4. Where detail structural analysis is carried out, ‘Unwelded’ stress values may be used away from heat affected zones and weld lines, see also Pt 4, Ch 2, 1.3 Aluminium 1.3.3.
5. For thickness less than 12,5 mm the minimum unwelded 0,2% proof stress is to be taken as 230 N/mm² and the minimum tensile strength is to be taken as 315 N/mm².