What are the primary aluminium alloys specified in this standard?

The standard specifies Aluminium-Magnesium alloys, particularly grade N8, which is suitable for marine environments (Clause 3.1, Table 1).

What is the main purpose of the 'bulb' on these plates?

The bulb acts as an integral flange to increase the section's moment of inertia and resistance to bending and local buckling, making it an efficient stiffener (Clause 1.1).

What are the minimum mechanical properties for an N8 alloy bulb plate?

For alloy N8, the minimum ultimate tensile strength is 295 MPa, the minimum 0.2% proof stress is 195 MPa, and the minimum elongation is 12% (Table 2).

What is the straightness tolerance for these bulb plates?

The deviation from straightness (camber) should not exceed L/1000, where L is the length of the plate (Clause 5.4.1).

IS 6476

: 1987

Aluminium bulb plates for marine application

CurrentSpecializedSpecificationBIMMaterials Science · Structural Engineering and Structural Sections

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This standard specifies the dimensions, sectional properties, tolerances, and material requirements for wrought aluminium and aluminium alloy bulb plates. These sections are primarily intended for use as structural stiffeners in marine applications like shipbuilding due to their high strength-to-weight ratio and corrosion resistance.

Aluminium bulb plates for marine application

Quick Reference Values

Specified alloy grade for marine useN8 (Aluminium-Magnesium alloy)

Min. Tensile Strength (Alloy N8)295 MPa

Min. 0.2% Proof Stress (Alloy N8)195 MPa

Min. Elongation on 5.65√S₀ gauge length (Alloy N8)12 %

Tolerance on depth (d <= 100mm)±1.5 mm

Tolerance on web thickness (t w <= 6mm)±0.50 mm

Practical Notes

The bulb at the edge of the plate significantly increases the section's bending stiffness and buckling resistance, making it more efficient than a simple flat bar for stiffening ship plating.

Alloy N8 is commonly specified due to its excellent weldability and resistance to corrosion in saltwater environments, a critical factor for marine structures.

Ensure dimensional tolerances, especially straightness (camber and sweep), are checked upon delivery as they are crucial for fitting and welding during hull construction.