RU2522691C2 - Membrane cargo capacity for liquefied natural gas transportation and storage - Google Patents

Abstract

FIELD: transport.

SUBSTANCE: invention relates to transport shipbuilding, means for marine freight and storage of liquefied natural gas (LNG) and concerns design of membrane cargo capacity for its transportation and storage. Reservoir for transportation and storage of LNG includes structured thermally insulated shell mounted on carrying structure of freight vessel or capacity. The shell consists of several layers. In this structure, one layer is metal and sealed and contacts with liquefied gas being transferred or stored. The layer contains undulating corrugations. Wave tops and troughs form zigzags. Undulating indents between corrugations on the outside are filled with porous synthetic material or paste based on chopped glass fibre and binding agent.

EFFECT: higher strength and reliability of membrane cargo capacity for liquefied natural gas transportation and storage, lower probability of sealing failure.

3 cl, 10 dwg

Description

The invention relates to the field of transport shipbuilding, means of sea transportation and storage of liquefied natural gas (LNG) and relates to the creation of a membrane cargo tank for its transportation and storage.

Known membrane cargo tank for transportation and storage of LNG, consisting of a composite shell forming a sealed and thermally insulated tank, built into the supporting structure of the vessel (European patents No. 248721 and No. 573327). The tank contains two airtight barriers, the primary barrier being in contact with the substance contained in the tank, and the secondary barrier is located between the primary barrier and the supporting structure; the aforementioned airtight barriers alternate with two thermally insulating barriers (primary and secondary).

French patents No. 1376525 and No. 1379651, as well as the patent of the Russian Federation 2282101, publ. 08/20/2006, Bulletin No. 23 (prototype) describe the design of a membrane cargo tank containing metal plates with wavy corrugations in contact with the LNG as a primary airtight barrier, on the surface of which two series of waves are formed, between which flat surfaces are located. The first series is perpendicular to the waves of the second series. The waves of one series have a height lower than the waves of the second series, so that the waves of the first series are interrupted when they intersect with the waves of the second series.

The disadvantages of this design solution is the low strength and reliability of the primary airtight barrier with external forces and temperature drops during filling and emptying of the cargo tank. These shortcomings are due to the following reasons:

- deep plastic deformation of the sheets of the primary barrier during its manufacture, associated with the need (to achieve the desired shape of the product) the formation of large residual deformations and stresses caused by local tension and compression, which very negatively affect the static and fatigue strength of the barrier in the future;

- the appearance of significant local stresses in areas of deep plastic deformation under static and dynamic external influences from the side of the transported (stored) liquid, as well as during thermal effects associated with filling (emptying) of the cargo tank with liquid.

The presence of such a drawback is especially negative for the creation of large cargo tanks, as well as for the operation of partially filled tanks, associated with the appearance of sloshing (beating of LNG on the side walls of the tank during transportation), and is expressed in the loss of tightness of the structure, in the plastic deformation of corrugated corrugations in the zone their intersection and in increasing the likelihood of fatigue cracks appearing in it. An increase in the thickness of the plates does not lead to the elimination of design flaws, as it increases the material consumption of the structure, reduces the flexibility of the airtight barrier, which is necessary (especially in the area of intersection of corrugated corrugations) to enable thermal compression and stretching of the plates without the risk of leakage.

The objective of the invention is to increase the strength and reliability of the membrane cargo tank for transporting and storing liquefied gas, reducing the likelihood of a violation of its tightness.

To achieve the specified technical result, the following solutions are proposed. According to the invention, the primary airtight barrier of the cargo tank is made in the form of a corrugated single-layer or two-layer plate, the corrugations having a wave-like shape, and the tops and troughs of the waves form a zigzag shape. With a single-layer design, the plate is made of stainless steel or aluminum alloy, with a two-layer design, the metal plate on the inside of the container has a fiberglass layer, which is the shape of the metal plate. The individual corrugated plates forming the primary airtight barrier are interconnected, and the metal sheets are connected by welding (mainly overlap). On the inside, the plate is in contact with liquefied natural gas. On the outside, the wavy holes of the plate are filled with porous synthetic material. As a filler, a composition based on polyurethane or polyvinyl chloride, spheroplastics, polystyrene, or a paste based on chopped glass fiber and a binder can be used.

The implementation of a sealed primary barrier in the form of a plate with wavy zigzag corrugations ensures its high compliance with temperature differences associated with pouring gas into the cargo tank or with its emptying, as well as low temperature stresses in the barrier structure. The presence of filler in the wells on the outside of the primary barrier provides a low level of stresses in the barrier structure due to static and dynamic force effects of the liquid. The absence of zones of intersection of the corrugations (their continuity) provides, with the same material consumption, a higher level of strength of the proposed design compared to the prototype. The presence of a second fiberglass layer from the inner side of the container for forming the metal sheet of the sealed primary barrier with fiberglass fabric (mainly biaxial or quadruple) makes it possible to use a small thickness of the metal plate (foil) in the manufacture of the sealed primary barrier and significantly increases the thermal insulation properties of this barrier.

The invention is illustrated by drawings, which show:

- a fragment of the tank for transporting and storing liquefied gas, which is the prototype of the invention (figure 1);

- the inner surface of the sealed primary barrier of the cargo capacity of the prototype (figure 2);

- a fragment of the proposed capacity for transportation and storage of liquefied gas (figure 3);

- the inner surface of the primary airtight barrier of the proposed cargo tank (figure 4);

- plan view of the primary airtight barrier of the proposed tank (figure 5);

- cross section of the primary airtight barrier along AA, the location of which is indicated in figure 5, with a single-layer execution of the corrugated plate (Fig.6);

- the cross section of the primary airtight barrier along LA, the location of which is indicated in figure 5, with a two-layer execution of the corrugated plate (Fig.7);

- the cross section of the primary tight barrier according to BB, the location of which is indicated in figure 5, with a single-layer execution of the corrugated plate (Fig. 8);

- the cross section of the primary tight barrier according to BB, the location of which is indicated in figure 5, with a two-layer execution of the corrugated plate (figure 9);

- a rational way of arranging corrugated plates interconnected when welding a sealed primary barrier of a cargo tank (figure 10).

The lists of structural elements 1-5 for the prototype and the proposed design are similar (figure 1, 3). The tank for transporting and storing liquefied gas contains a primary sealed barrier 1, a secondary sealed barrier 2, a primary heat-insulated barrier 3, a secondary heat-insulated barrier 4. The tank is mounted on the power structure 5 of the ship's hull. The primary sealed barrier includes a corrugated metal plate 6 and a hole filler on the outside of the barrier 7.

The achievement of the technical result using the proposed design of the tank for transporting and storing liquefied gas is as follows. With temperature differences associated with pouring gas into the cargo tank or with its emptying, the temperature expansion or narrowing of the metal plate elements of the sealed primary barrier is accompanied by their bending in the areas of the peaks and troughs of the wave surfaces of the corrugations and negligibly small stretching or compression of the middle surfaces of the plates. As a result, the chain temperature stresses in the plate are extremely small, and the bending temperature stresses cannot reach significant values due to the small thickness of the plate. The high flexibility of the filler holes, due to significantly lower values of the elastic characteristics of polymeric materials compared to metal, provides a low level of temperature stresses in the filler. At the same time, it effectively transfers liquid pressure to the primary heat-insulating barrier, eliminating the appearance of large stresses in the metal plate caused by this pressure.

It is recommended that the individual plates of the airtight barrier be joined along the lateral edges by welding so that adjacent plates have mutually perpendicular orientations of the corrugations (in this case, plates with different corrugation orientations are staggered), which further reduces temperature stresses.

Thus, the proposed design of the hull allows you to reduce the level of tension of the elements of the primary airtight barrier, to increase the reliability and strength of the membrane cargo tank for transporting and storing liquefied gas and to reduce the likelihood of violation of its tightness, which distinguishes it from the prototype.

Claims (3)

1. A tank for transporting or storing liquefied natural gas, containing a structured thermally insulated shell, mounted on a supporting structure of a transport vessel or tank for storing liquefied gas and consisting of several layers, at least one of which is metal, sealed, is in contact with transported or stored liquefied gas and contains wave-like corrugations, characterized in that the tops and troughs of the waves form a zigzag shape, wave-shaped holes between the corrugations from the outside the sides are filled with porous synthetic material or paste based on chopped fiberglass and a binder. 2. The tank for transporting or storing liquefied natural gas according to claim 1, characterized in that the sealed layer in contact with the transported or stored liquefied gas is a corrugated metal plate molded from the inside of the container with fiberglass. 3. A tank for transporting or storing liquefied natural gas according to claims 1 and 2, characterized in that the plates connected (by welding) along the lateral edges have mutually perpendicular directions of orientation of the corrugations, and plates with different orientation of the corrugations are staggered.

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