Common Structural Rules - Common Structural Rules for Bulk Carriers and Oil Tankers, January 2019 - Part 1 General Hull Requirements - Chapter 3 Structural Design Principles - Section 1 Materials - 4 Aluminium Alloys
4 Aluminium Alloys
4.1 General
4.1.1 The use of aluminium alloys in superstructures, deckhouses, hatch covers, helicopter platforms, or other local components is to be specially considered. A specification of the proposed alloys and their proposed method of fabrication is to be submitted for approval.
Material requirements and scantlings are to comply with the Rules for Materials of the Society. Series 5000 aluminium-magnesium alloys or series 6000 aluminium-magnesium-silicon alloys are to be used.
4.1.2 In the case of structures subjected to low service temperatures or intended for other specific applications, the alloys to be employed are to be agreed by the Society.
4.1.3 Unless otherwise agreed, the Young’s modulus for aluminium alloys is equal to 70,000 N/mm2 and the Poisson’s ratio equal to 0.33.
4.1.4 Details of the proposed method of joining any aluminium and steel structures are to be submitted for approval.
4.2 Extruded plating
4.2.1 Extrusions with built-in plating and stiffeners, referred to as extruded plating, may be used.
4.2.2 In general, the application of extruded plating is limited to decks, bulkheads, superstructures and deckhouses. Other uses may be permitted by the Society on a case-by-case basis.
4.2.3 Extruded plating is to be oriented so that the stiffeners are parallel to the direction of main stresses.
4.2.4 Connections between extruded plating and primary members are to be given special attention.
4.3 Mechanical properties of weld joints
4.3.1 Welding heat input lowers locally the mechanical strength of aluminium alloys hardened by work hardening (series 5000 other than condition O or H111) or by heat treatment (series 6000).
4.3.2 The as-welded properties of aluminium alloys of series 5000 are in general those of condition O or H111. Higher mechanical characteristics may be considered, provided they are duly justified.
4.3.3 The as-welded properties of aluminium alloys of series 6000 are to be agreed by the Society.
4.4 Material factor, k
4.4.1 The material factor, k for aluminium alloys is to be obtained from the following formula:
where:
R’lim : Minimum guaranteed yield stress of the parent metal in welded condition R’p0.2, in N/mm2, but not to be taken greater than 70% of the minimum guaranteed tensile strength of the parent metal in welded condition R’m, in N/mm2.
R’p0.2 : Minimum guaranteed yield stress, in N/mm2, of material in welded condition.
R′ p0.2 = η1Rp0.2
R’m : Minimum guaranteed tensile strength, in N/mm2, of material in welded condition.
R'm = η2Rm
Rp0.2 : Minimum guaranteed yield stress, in N/mm2, of the parent metal in delivery condition.
Rm : Minimum guaranteed tensile strength, in N/mm2, of the parent metal in delivery condition.
η1, η2 : Specified in Table 9.
Table 9 : Aluminium alloys - Coefficients for welded construction
| Aluminium alloy | η1 | η2 |
|---|---|---|
| Alloys without work-hardening treatment (series 5000 in annealed condition O or annealed flattened condition H111) | 1 | 1 |
| Alloys hardened by work hardening (series 5000 other than condition O or H111) | R’p0.2 / Rp0.2 | R’m / Rm |
| Alloys hardened by heat treatment (series 6000) (1) | R’p0.2 / Rp0.2 | 0.6 |
| (1) When no information is available, coefficient η1 is to be taken equal to the metallurgical efficiency coefficient β as defined in Table 10. | ||
Table 10 : Aluminium alloys - Metallurgical efficiency coefficient β
| Aluminium alloy | Temper condition | As-built thickness, in mm | β |
|---|---|---|---|
| 6005A (Open sections) | T5 or T6 | t ≤ 6 | 0.45 |
| t > 6 | 0.40 | ||
| 6005A (Closed sections) | T5 or T6 | All | 0.50 |
| 6061 (Sections) | T6 | All | 0.53 |
| 6082 (Sections) | T6 | All | 0.45 |
4.4.2 In the case of welding of two different aluminium alloys, the material factor, k to be considered for the scantlings is the greater material factor of the aluminium alloys of the assembly.
4.5 Others
4.5.1 Aluminium fittings in tanks used for the carriage of oil, and in cofferdams and pump rooms are to be avoided. Where fitted, aluminium fittings, units and supports, in tanks used for the carriage of oil, cofferdams and pump rooms are to satisfy the requirements of Pt 2, Ch 2, Sec 2, [1.2] for aluminium anodes.
4.5.2 The underside of heavy portable aluminium structures such as gangways, is to be protected by means of a hard plastic or wood cover, or other approved means, in order to avoid the creation of smears. Such protection is to be permanently and securely attached to the structures.
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