Ships – Building – Freighters
Reexamination Certificate
2002-07-01
2004-01-13
Basinger, Sherman (Department: 3617)
Ships
Building
Freighters
C220S560070, C220S560110, C220S560120, C220S560150, C220S901000
Reexamination Certificate
active
06675731
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a watertight and thermally insulating tank, particularly for storing liquefied gases, such as liquefied natural gases with high methane content, at a temperature of about −160° C., the said tank being built into a bearing structure of a ship, particularly the hull of a ship intended for transporting liquefied gases by sea.
The present invention relates more particularly to a watertight and thermally insulating tank built into a bearing structure of a ship, the said bearing structure being of polygonal cross section and comprising a number of practically flat rigid walls adjacent via their longitudinal edges, at least one of the said walls having a variable width over at least part of the length of the wall, the solid angles of intersection of the bearing structure which are formed by the said variable-width wall and the adjacent walls being orientated obliquely.
DESCRIPTION OF THE RELATED ART
A tank comprising two successive watertightness barriers, one of them a primary barrier in contact with the product contained in the tank and the other a secondary barrier arranged between the primary barrier and the bearing structure, these two watertightness barriers alternating with two thermally insulating barriers, a primary one and a secondary one respectively, is known, particularly from French Patent Application 2 724 623.
In the aforementioned application, the secondary barriers and the primary insulating barrier essentially consist of a collection of practically parallelepipedal prefabricated panels fixed mechanically to the walls of the bearing structure, each panel being formed, firstly, of a first rigid plate carrying a layer of thermal insulation and with it constituting a secondary insulating barrier element, secondly, of a flexible sheet adhering to practically the entire surface of the layer of thermal insulation of the aforementioned insulating barrier element, the said sheet comprising at least one continuous thin metal foil forming a secondary watertightness barrier element, thirdly, of a second layer of thermal insulation adhering to the aforementioned sheet, of a second rigid plate covering the second layer of thermal insulation and with it constituting a primary insulating barrier element. The primary watertightness barrier consists of metal strakes, for example made of Invar, held mechanically so as to slide on the rigid plate of the primary insulating barrier by their turned-up longitudinal edges.
Each prefabricated panel has the overall shape of a rectangular parallelepiped, the secondary insulating barrier element and the primary insulating barrier element having, respectively, viewed in plan view, the shape of a first rectangle and of a second rectangle, the sides of which are practically parallel, the length and/or width of the second rectangle being shorter than that (those) of the first rectangle so as to form a peripheral rim.
The peripheral rims of adjacent panels and the lateral walls of the primary insulating barrier elements define joining regions which are filled with insulating tiles each consisting of a layer of thermal insulation, covered by a rigid plate, the rigid plates of the insulating tiles and the second rigid plates of the panels constituting a practically continuous wall able to support the primary watertightness barrier, the regions where the secondary insulating barrier elements meet being filled with connectors made of insulating material. To ensure the continuity of the watertightness of the secondary watertightness barrier at the join between two panels, the rims are, before the joining tiles are fitted, covered with a band of flexible sheet comprising at least a continuous thin metal foil, the said band adhering to the adjacent lateral rims.
It is known that the cooling of the tank generates, at the primary and secondary watertightness barriers, tensile stresses which add to the tensile stresses generated in these watertightness barriers by the deformation of the beam that constitutes the ship when the ship is moving in the swell. When practically flat Invar-plate strakes are used, the movements of thermal contraction are of limited amplitude, but nonetheless remain. In a known way, the metal strakes, slideably mounted on the prefabricated panels, are fixed at their ends to the bearing structure of the ship by a rigid corner structure such as those described in French Patents 2 709 725 and 2 780 942, so that tensile forces in the longitudinal direction of the strakes are transmitted to the bearing structure.
The bearing structure to which the panels are fixed is formed from the walls of the double hull of the ship. The walls of the double hull form compartments each defined by a number of practically flat longitudinal walls adjacent by their longitudinal edges and having a polygonal cross section in the shape of a polyhedron, particularly an irregular octahedron, the angles at the solid angles of intersection of two adjacent longitudinal walls of which generally measure 90° or 135°, and two transverse partitions at the longitudinal ends of the compartment, parallel to one another and perpendicular to the longitudinal walls. The longitudinal walls and the transverse partitions of a compartment constitute the bearing structure of the tank. In general, the longitudinal walls are arranged more or less in a cone with a polygonal directrix curve, in the bow part of the said ship and also in its stern part, and as a cylinder with a polygonal directrix curve in the remainder of the ship.
To produce a tank built into a compartment of constant cross section, comprising only rectangular longitudinal walls, the prefabricated panels are arranged side by side parallel to the axis of the tank, and the strakes are arranged longitudinally on the panels. In the case of a tank intended to be built into the front of the ship, the compartment generally has at least one bottom wall and a roof wall of trapezoidal shape, the cross section of which decreases towards the front of the ship. On these walls of trapezoidal shape, the prefabricated panels are also arranged parallel to the axis of the tank and cut to suit the oblique solid angles of intersection, the strakes being held parallel to the longitudinal axis and cut obliquely at the ends to tailor them to the oblique solid angles of intersection. The end of each strake is fixed at an angle to a vertical pillar, itself fixed to the bearing structure at the oblique solid angle of intersection. To allow this fixing, the pillar is formed of two stainless steel posts welded one on each side of an Invar mounting plate to which the strake is welded, the secondary watertightness barrier also being fixed to the said mounting plate.
A fixing such as this establishes a direct thermal bridge between the primary barrier and the bearing structure, and this is prejudicial in terms of insulating performance. Furthermore, such a structure has numerous disadvantages. Producing the pillars entails heterogeneous welding which is tricky to implement. Access to the pillars is relatively difficult and makes the operation of welding the strakes to the mounting plate painstaking. The size of the pillars makes filling the corner structures at the solid angles of intersection with insulating tiles more difficult. In addition, the pillars have a tendency to twist because the strakes are fixed to them at an angle.
SUMMARY OF THE INVENTION
The object of the invention is to propose a tank built into a bearing structure with obliquely orientated solid angles of intersection which make it possible to alleviate the aforementioned drawbacks.
To achieve this, the present invention proposes a watertight and thermally insulating tank built into a bearing structure particularly of a ship, the said bearing structure being of polygonal cross section and comprising a number of practically flat rigid walls adjacent by their longitudinal edges, at least one of the said walls having a width that varies over at least part of the length of the wall, the solid angles of intersection of
Basinger Sherman
Gaz Transport & Technigaz
Young & Thompson
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