Section 2 Materials

2.1.1 The materials used in the construction of the craft are to be manufactured and tested in accordance with the appropriate requirements of Ch 8 Aluminium Alloysthe Rules for the Manufacture, Testing and Certification of Materials (hereinafter referred to as the Rules for Materials).

2.1.2 As an alternative to Pt 7, Ch 2, 2.1 General 2.1.1, materials may be accepted for specific applications, provided they are manufactured and tested in accordance with the requirements of national or proprietary specifications which give reasonable equivalence to the requirements of the Rules for the Manufacture, Testing and Certification of Materials, July 2022. Additional tests may be required to prove that the materials are suitable for the intended purpose in respect of mechanical properties, weldability and corrosion resistance.

2.1.3 All materials are to be manufactured at works which have been approved by LR for the type and, where appropriate, grade of aluminium which is being supplied and for the relevant aluminium production and processing route.

2.2.1 Materials are, in general, to be limited to the supply conditions detailed in Ch 8, 1.6 Heat treatment of the Rules for Materials. Other supply conditions may be accepted but, as materials in a condition other than annealed are subject to a loss of mechanical strength in the vicinity of welded joints, the strength used in design calculations are to be as given in Pt 7, Ch 2, 2.4 Mechanical properties for design.

2.2.2 For applications where the material will be subject to high local stresses, it is recommended that the scantlings, when using higher strength materials, be determined on the basis of the mechanical properties of the material in the as-welded annealed condition.

2.3.1 All structural castings are to be manufactured and tested in accordance with the appropriate requirements of Ch 8, 3 Aluminium alloy castings.

2.4.1 The minimum tensile strength properties of aluminium alloys approved for structural use are given in Ch 13, 8.3 Fabrication and welding 8.3.2 of the Rules for Materials. Other alloys and conditions of temper may be accepted in accordance with Pt 7, Ch 2, 2.1 General 2.1.3.

2.4.2 In general, for welded structure, the maximum value for the strength of the material, σ_a, to be used in the scantling derivation is that of the aluminium alloy in the welded condition, where σ_a is defined as the 0,2 percent butt welded proof stress or 70 per cent of the ultimate strength of the material in the welded condition in N/mm², whichever is the lesser.

2.4.3 The tensile modulus of elasticity to be used in scantling calculations is 69 x 10³ N/mm² for all aluminium alloy materials.

2.4.4 The type of material, specification to which it is manufactured (including grade and temper) and minimum guaranteed mechanical properties are to be indicated on the construction drawings.

2.5.1 The potential of the aluminium-magnesium (5000 Series) and the aluminium-magnesium-silicon (6000 Series) alloys is generally in the range -0,7 to -0,9 Volts with reference to a silver/silver chloride sea water reference electrode. A negative potential swing of at least 0,1 Volts from the corrosion potential is necessary to provide cathodic protection in sea water (i.e. -0,8 to -1,0 Volts). The limit of negative potential is, however, not to exceed -1,1 Volts with reference to a silver/silver chloride sea water reference electrode. Zinc or aluminium-zinc-indium or aluminium-zinc-tin anodes may be used for cathodic protection but aluminium anodes containing mercury are not acceptable.

2.5.2 Where a cathodic protection system is fitted, plans showing the proposed layout of anodes and hull penetrations are to be submitted in accordance with Ch 15 Corrosion Prevention of the Rules for Materials.

2.6.1 The hull, deck, deckhouse and superstructure and other structure which is exposed to the marine environment is to be protected against corrosion by a suitable protective coating, see Ch 15 Corrosion Prevention of the Rules for Materials. Internal structures need not in general be coated provided that they are built of aluminium alloy grades shown in Ch 8 Aluminium Alloys of the Rules for Materials.

2.6.2 Aluminium alloy is to be suitably cleaned, cleared of oxide and degreased before the application of any protective coating.

2.6.3 Paints containing lead, mercury or copper are not to be used in conjunction with aluminium alloys.

2.7.1 Where bimetallic connections are made, involving dissimilar metals, measures are to be incorporated to preclude galvanic corrosion. In order to prevent galvanic corrosion, special attention is to be given to the penetrations of and connections to the hull, bulkheads and decks by piping and equipment where dissimilar materials are involved.

2.8.1 The design is to ensure that the location of all bimetallic connections allows for regular inspection and maintenance of the joints and penetrations during service.

2.9.1 Where plated decks are sheathed with wood, the sheathing is to be efficiently attached to the deck, caulked and sealed, to the satisfaction of the Surveyor in accordance with the approved drawings.

2.9.2 Deck coverings in the following positions are to be of a type which will not readily ignite where used on decks:

1. Forming the crown of machinery or cargo spaces within accommodation spaces of cargo craft.

2. Within accommodation spaces, control stations, stairways and corridors of passenger craft.

2.10.1 The scantlings determined from the formulae provided in the Rules assume that the materials used are selected, manufactured and protected in such a way that there is negligible loss in strength by corrosion.

2.10.2 Where aluminium alloy is not protected against corrosion, by painting or other approved means, the scantlings may require to be further considered.

2.11.1 Aluminium alloys in commercial use are in general not subject to unstable crack growth in an elastic stress field because fracture toughness is high. However, for alloys with higher strength and/or temper, special tests may be required to provide information on fracture toughness.

2.11.2 Construction procedures, materials and welding are to be in accordance with the requirements of this Chapter such that stress corrosion cracking is avoided.

2.11.3 High local stresses are to be avoided by the use of suitable design detail, see also LR's Guidance Notes for Structural Details.