Membrane tank

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A membrane tank is a type of cargo tank used in tanker shipping for the transport of liquefied gases .

These are non-self-supporting tanks, which consist of a thin sheet metal membrane of 0.5 to 1.5 mm Invar , nickel or stainless steel and are supported by an insulating layer on the load-bearing ship formations. The membrane is designed in such a way that it can absorb greater temperature-related expansions due to the material properties and appropriately arranged folds and beads . When transporting liquefied gases, for example, with LNG as cargo, temperatures of −164 ° C to −161 ° C occur. When the ship is in the yard, the temperature in the tank can reach 40 ° C or more.

A so-called second barrier made of plywood or Invar is attached around the sheet metal membrane, which is intended to hold up the leaking liquid gas for a defined period of time in the event of a leak. [Proof?] The tank insulation consists of perlite , rock wool , polyurethane foam , balsa wood and plywood. On the one hand, the insulation should prevent the liquefied gas from heating up and, on the other hand, protect the non- cold-resistant shipbuilding steel from brittle fracture .

Membrane tanks have advantages and disadvantages compared to conventional spherical or cylinder tanks:

Membrane tanks allow the tanks to be optimally adapted to the shape of the ship and are also suitable for smaller ships. In addition, cooling or warming up comparatively quickly is possible without overstressing the tank material.
In contrast, the folds of older ships tend to leak. Due to the thin container wall, the maximum possible tank pressure is lower. Membrane tanks have to be driven either completely full or almost empty, as otherwise there is a risk of damage to the membrane due to free surfaces in rough seas .