What are the tensile strength requirements for manhole covers on ships

When choosing and arranging manhole covers for ships, in addition to abiding by relevant conventions, rules and regulations, strength, application and ease of use must also be taken into consideration.

The strength of Marine manhole covers is mainly reflected in the thickness of the cover plate and the number of fixing screws. Generally speaking, the thickness of the deck plate should not be less than that of the hull structure steel plate on which the deck is installed. As the cover plate is more prone to corrosion than the structural steel hull plate, the manhole cover for ships should be adopted. When the thickness of the hull structure steel plate at the installation position is less than 10 millimeters, the thickness of the cover plate should be 1 millimeter greater than that of the hull structure steel plate at the installation position. If the deck or bulkhead on which the manhole cover is installed is determined by strength calculation, the thickness of the manhole cover should be able to withstand the same water pressure conditions.

The structure of the manhole cover for ships must be selected appropriately according to the sealing requirements of the exhibition stand and the installation space. Seawater-resistant rubber should be used as waterproof gaskets for manhole covers in freshwater tanks, ballast tanks, front and rear tanks and other places. The oil well covers at oil tanks, lubricating oil tanks, drainage tanks and other places should use impact-resistant rubber as gaskets. The bottom of the cabin will adopt A-type manhole covers with shells, which are prone to water and oil accumulation, such as the upper part of the cabin and the drinking water tank. When installing manhole covers that may affect people's activities in passageways, living rooms and workshops, underground manhole covers should be chosen. The manhole cover of the jet fuel tank must be made of brass to prevent spark impact. When the manhole cover can be used for a long time in a humid environment, its bolts or studs are made of stainless steel. Nuts are made of stainless steel, brass or galvanized steel.

From the perspective of the usage of manhole covers, large-sized through holes facilitate people's access. However, due to factors such as the hull structure, mechanical equipment, and pipeline layout, the size of manhole covers is usually limited to flat positions. It is more appropriate to install manhole covers with a through hole size of 500mm to 400mm on the inner bottom plate. Unless the layout is truly difficult, please do not use through-hole sizes of 450mm-350mm to cover the structure of the exhibition stand or other vertical positions. A manhole of 600 to 450 millimeters should be placed on the top surface, and its long axis should be in the vertical direction. The height from the ground where a person is located to the lower edge of the through hole should not be less than 500mm so that a person can pass through.