Why aluminum circle is for oil tight hatch cover
The oil-tight hatch cover is made of aluminum alloy, which leverages the advantages of aluminum alloy such as light weight, high strength, resistance to seawater corrosion, rust resistance, and easy processing. This not only significantly reduces the load on the ship's superstructure and lowers fuel consumption during operation, but also eliminates the need for heavy anti-corrosion coating maintenance costs. At the same time, it meets the requirements of controllable structural deformation under oil-tight sealing conditions and long-term adaptability to the oil environment in the ship's tanks.
The mainstream aluminum alloys suitable for marine use include 5052, 5083, and 5086 rust-resistant aluminum-magnesium alloys, which balance corrosion resistance and structural strength. For heavy-load conditions, 6061 and 6082 heat-treated and strengthened aluminum alloys can be selected.
Aluminum round disc specification
Alloys | Adaptable hatch clear opening(mm） | Diameter(mm) | Thickness(mm) | Diameter tolerance(mm) |
5083-h116/h321 | Φ600~Φ1200 | 630-1230 | 10-12.5 | ±0.5 |
5086-h112 | Φ400~Φ800 | 430-830 | 8-10 | |
5052-h32 | Φ300~Φ500 | 330-530 | 6-8 |
Aluminum circle alloys
1. 5052 aluminum circle
Applications: Small, atmospheric pressure lubricating oil tank maintenance oil-tight discs (300-500mm diameter), in areas with low internal pressure and low load, suitable for secondary locations in near-shore environments. Typical thickness is 6-8mm, no reinforcement required.
Limitations: Cannot withstand heavy pressure and oil pressure fluctuations; not suitable for main fuel tanks.
2. 5086 Aluminum Discs
Applications: Small to medium-sized oil-tight tank covers (400-800mm diameter), conventional manholes for fuel oil and lubricating oil tanks on near-shore vessels. The minimum thickness of the substrate without reinforcing ribs is 8-10 mm; the substrate with annular and radial reinforcing ribs is 6–8 mm.
Limitations: Insufficient reliability in high-strength ocean-going main fuel tanks and heavy-load decks.
3. 5083 (H116/H321) Aluminum Discs
Applications: 600–1200mm diameter oil-tight hatch covers for main cargo oil tanks and heavy-load deck areas on ocean-going vessels. The minimum thickness of the substrate without reinforcing ribs is 10–12.5 mm; the substrate with annular and radial reinforcing ribs is 6–10 mm.
Advantages: Strong sealing stability; resistant to deformation and oil leakage under prolonged stress; The only disadvantage is the relatively high aluminum circle cost.
FAQs
1. What is an aluminum circle for an oil-tight hatch cover?
An aluminum circle is a round aluminum plate or disc used as the main cover plate for an oil-tight hatch, inspection opening, manhole, fuel tank access cover, lube-oil tank cover, or hydraulic tank cover.
It may be supplied as:
Plain round blank;
Drilled bolt-hole cover;
Machined cover with gasket groove;
Reinforced cover with ribs or stiffeners;
Hinged hatch cover assembly.
2. Which aluminum alloy is best for an oil-tight hatch cover?
For marine and offshore applications, the preferred alloy is usually:
AA 5083-H116 or H321
Other suitable options include:
AA 5086-H111/H116 — marine welded structures;
AA 5052-H32/H34 — small, low-load, indoor oil tank covers;
AA 5754 — moderate-duty industrial covers;
AA 6061-T6 / AA 6082-T6 — machined components, hinges, locking parts, or extruded frames.
For a cover exposed to seawater, salt spray, or deck weather, 5083 is generally the first choice.
3. Is aluminum itself "oil-tight"?
No. Aluminum is a solid metal and does not absorb oil, but the complete hatch-cover assembly becomes oil-tight only when it has:
A properly designed gasket or O-ring;
Smooth and flat sealing surfaces;
Adequate and uniform clamping force;
Correct bolt, dog clamp, or locking arrangement;
Sufficient cover stiffness to prevent deflection;
Good welding and fabrication quality.
4. Can 5052 aluminum be used instead of 5083?
Yes, but generally for less demanding service.
5052 is suitable for:
Small inspection covers;
Indoor oil tanks;
Light-duty hydraulic or lube-oil covers;
Covers without high mechanical loading.
5083 aluminum is better for:
Marine deck installations;
Fuel oil and ballast-area exposure;
Large-diameter covers;
Welded structures;
Walk-on covers;
Saltwater and offshore conditions.
Original source: https://www.aluminum-circle.com/application/aluminum-circle-for-oil-tight-hatch-cover.html
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