WO2007142400A1

WO2007142400A1 - Extended spherical lng storage tank and method for manufacturing the same

Info

Publication number: WO2007142400A1
Application number: PCT/KR2007/000890
Authority: WO
Inventors: Keh-Sik Min; Oi-Hyun Kim; Jin-Soo Park; Ick-Hung Choe; Sang-Hoon Shin; Bong-Jae Kwon; Il-Keun Kwon
Original assignee: Hyundai Heavy Industries Co., Ltd.
Priority date: 2006-06-05
Filing date: 2007-02-21
Publication date: 2007-12-13
Also published as: NO335482B1; NO20085116L; JP2013007486A; JP2009540233A; JP5603906B2

Abstract

The present invention provides an extended spherical LNG storage tank, installed on an LNG tanker, and a method for manufacturing the same, in which the junctions between a connection tank part and upper and lower tank parts are configured as smooth parts, thus increasing the LNG storage capacity of the tank and mitigating stress concentration on the junctions, and the connection tank part is constructed by integrating a plurality of plates into a single structure, thus increasing work efficiency while fabricating the connection tank part and thereby enabling quick and easy production of the LNG storage tanks. In the extended spherical LNG storage tank, which includes the upper and lower tank parts, each having a predetermined radius of curvature R, and the connection tank part provided between the upper and lower tank parts so as to increase the LNG storage capacity of the tank, the connection tank part is defined by a circular arc or a parabola C3, which is circumscribed with two circles Cl and C2, which define the upper tank part and the lower tank part, respectively, outside the two circles Cl and C2.

Description

[DESCRIPTION]

[invention Title]

EXTENDED SPHERICAL LNG STORAGE TANK AND METHOD FOR MANUFACTURING THE SAME [Technical Field]

The present invention relates, in general, to extended spherical LNG storage tanks and methods for manufacturing the same and, more particularly, to an extended spherical LNG storage tank and a method for manufacturing the same, in which the junctions between a connection tank part and upper and lower tank parts are configured as smooth parts during a process for integrating the connection tank part with the upper and lower tank parts into a spherical LNG storage tank so as to increase the LNG storage capacity of the tank, thus mitigating stress concentration on the connection tank part and effectively increasing the LNG storage capacity of the tank, in which the connection tank part is constructed by welding a plurality of plates to each other into a single structure, thus increasing • work efficiency while fabricating the connection tank part, and the thickness of the connection tank part is gradually increased in a direction toward the lower part thereof, thus further mitigating the stress concentration on the connection tank part. [Background Art] As shown in FIG. 1, conventional spherical LNG storage tanks 9, which are installed on an LNG tanker 100, are typically the same size. Further, the line of vision 103 of a helmsman, which must include a minimum visual range 102 in front of the prow of the LNG tanker 100 required to ensure the safe travel of the tanker 100, is determined both by the height of a pilot house 101 and by the height of a spherical LNG storage tank 9 installed on the prow of the LNG tanker 100.

Thus, a spherical LNG storage tank, which is installed on the LNG tanker 100 at a location in back of the spherical LNG storage tank 9 placed on the prow of the LNG tanker 100, may have an increased height, which is increased up to the line of vision 103.

Described in detail, when a plurality of cylinder-inserted LNG storage tanks 11 is installed on an LNG tanker 100 at respective locations in back of the prow LNG storage tank such that the heights of the cylinder-inserted LNG storage tanks 11 are sequentially increased to correspond to the line of vision 103 of the helmsman, the LNG storage capacity of the LNG tanker 100 can be increased without increasing the size of the LNG tanker 100, in comparison with an LNG tanker provided with spherical LNG storage tanks 9 that are all the same size. FIG. 3 is a view illustrating the structure of a conventional cylinder-inserted LNG storage tank having an increased LNG storage capacity. As shown in the drawing, the cylinder-inserted LNG storage tank 11 comprises: hemispherical upper and lower tank parts 20 and 30, which have the same radius of curvature; a cylindrical connection tank part 40a, which connects the upper tank part 20 to the lower tank part 30 and increases the LNG storage capacity of the tank 11; and a support skirt 50, which is provided around an equatorial part 45 of the cylindrical connection tank part 40a and is secured to the deck of the LNG tanker, thus supporting the cylinder- inserted LNG storage tank 11 on the deck. However, the longitudinal section of the cylindrical connection tank part 40a is oriented vertically, so that, if the length of the cylindrical connection tank part 40a is excessively increased in order to realize increased LNG storage capacity, stress may be concentrated both on the junctions between the cylindrical connection tank part 40a and the upper and lower tank parts 20 and 30, which have a predetermined curvature, and on the cylindrical connection tank part 40a. [Disclosure] [Technical Problem] Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide an extended spherical LNG storage tank, installed on an LNG tanker, and a method for manufacturing the same, in which the junctions between a connection tank part and upper and lower tank parts are configured as smooth parts, thus increasing the LNG storage capacity of the tank and mitigating stress concentration on the junctions, and the connection tank part is constructed by integrating a plurality of plates into a single structure, thus increasing work efficiency while fabricating the connection tank part, thereby quickly and easily producing the LNG storage tanks . [Technical Solution]

In order to accomplish the above object, in an aspect, the present invention provides an extended spherical LNG storage tank, comprising an upper tank part and a lower tank part, each having a predetermined radius of curvature R, and a connection tank part provided between the upper tank part and the lower tank part so as to increase LNG storage capacity of the LNG storage tank, wherein the connection tank part is defined by a circular arc or a parabola c3, which is circumscribed with two circles Cl and C2 that define the upper tank part and the lower tank part, respectively, outside the two circles Cl and C2.

In the extended spherical LNG storage tank, the connection tank part may be defined by a circular arc C3 having a start point and an end point at respective crossing points, at which lines, extending from a point on a center line that horizontally passes through a center of the connection tank part and passing through centers of curvature of the upper and lower tank parts, cross the circular arcs of the upper and lower tank parts, respectively, and the circular arc of the connection tank part having a radius of curvature Rl defined by a distance from the point on the center line of the connection tank part to each of the crossing points.

The connection tank part may be defined by a parabola having a start point at a point on the circular arc of the upper tank part and having an end point at a point on the circular arc of the lower tank part, wherein the start point and the end point are symmetrical to each other and tangential gradients of the parabola at the start and end points are equal to tangential gradients of the upper and lower tank parts at the start and end points.

Further, the connection tank part may be fabricated by integrating a plurality of plates into a single structure.

The connection tank part may comprise: a first connection unit and a second connection unit, which are placed at upper and lower locations in the connection tank part, respectively, and an equatorial part assembled with a lower part of the second connection unit and a support skirt supporting therearound.

Further, the connection tank part may comprise: a first connection unit, a second connection unit and a third connection unit, which are placed at upper, lower and middle locations in the connection tank part, respectively, and an equatorial part assembled with a lower part of the second connection unit and a support skirt supporting therearound.

Each of the first connection unit and the second connection unit may have a circular truncated conical shape. The connection tank part may have a thickness which is increased in a downward direction.

In another aspect, the present invention provides a method for manufacturing an extended spherical LNG storage tank, comprising: producing each of an upper tank part and a lower tank part by assembling a plurality of plates into a single structure; producing a connection tank part, having a radius of curvature larger than that of each of the upper and lower tank parts, by assembling a plurality of plates into a single structure; producing a support skirt, the support skirt being mounted to the connection tank part and securely installed on a deck of an LNG tanker so as to support the LNG storage tank on the deck; and mounting the connection tank part on a top of the lower tank part, vertically installing a pipe tower on a center of the lower tank part, mounting the support skirt around a circumference of the connection tank part, and mounting the upper tank part on a top of the connection tank part such that a top of the upper tank part is connected to the pipe tower.

Hereinbelow, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings .

FIG. 4 is a diagram showing an extended spherical LNG storage tank according to the present invention. As shown in the drawing, the extended spherical LNG storage tank 10 according to the present invention comprises: an upper tank part 20 and a lower tank part 30, each defined by a circular arc having a radius of curvature R; a connection tank part 40, which is defined by a circular arc having a radius of curvature larger than the radius R of each tank part 20, 30, is welded at an upper edge thereof to the lower edge of the upper tank part 20, and is welded at a lower edge thereof to the upper edge of the lower tank part 30; and a support skirt 50, which is mounted to an equatorial part 45, provided around the circumference of a lower part of the connection tank part 40, thus supporting the extended spherical LNG storage tank 10 on the deck of the LNG tanker.

FIG. 5 is a diagram illustrating the concept of a connection tank part of the LNG storage tank according to the present invention. As shown in the drawing, the connection tank part 40 is defined by a circular arc or a parabola C3, which is circumscribed with two circles Cl and C2, which define the upper tank part 20 and the lower tank part 30, respectively, outside the two circles Cl and C2, such that the connection tank part 40 connects the upper tank part 20 and the lower tank part 30 to each other.

In the present invention, the junctions between the connection tank part 40 and the upper and lower tank parts 20 and 30 are configured as smooth parts, thus mitigating stress concentration on the connection tank part 40 and effectively increasing the LNG storage capacity of the tank 10.

FIG. 6 is a diagram illustrating the concept of the extension structure of the LNG storage tank 10 according to a first embodiment of the present invention. As shown in the drawing, the extended spherical LNG storage tank 10 according to the first embodiment of the present invention comprises an upper tank part 20 and a lower tank part 30, which are defined by respective circular arcs having a radius of curvature R based on respective central points O and O' , and a connection tank part 40, which is defined by a circular arc having a radius of curvature Rl, larger than the radius R of each tank part 20, 30, and is welded at the upper edge thereof to the lower edge of the upper tank part 20 and is welded at the lower edge thereof to the upper edge of the lower tank part 30.

Here, the circular arc of the connection tank part 40 is configured as a smooth arc, which is designed such that the gradient of the upper end point of the connection tank part 40 at an upper junction point E between the upper tank part 20 and the connection tank part 40 is equal to the gradient of the circular arc of the upper tank part 20 at the junction point E, and which extends to a lower junction point G between the lower tank part 30 and the connection tank part 40. In other words, at the junction point E, the tangential gradient 80 of the connection tank part 40 is equal to the tangential gradient 80 of the circular arc of the upper tank part 20. In the same manner, at the junction point G, the tangential gradient 80 of the circular arc of the lower tank part 30 is equal to the tangential gradient 80 of the connection tank part 40.

Therefore, the connection tank part 40 is defined by a circular arc, which starts at the point E, ends at the point G and has a radius of curvature Rl . Further, the radius Rl of the connection tank part 40 is the length of a line segment, which extends from a point J on a line segment AB, which is the center line, horizontally passing through the center of the connection tank part 40, to the junction point E of the circular arc of the upper tank part 20, while passing through the center O of the circular arc of the upper tank part 20. That is, the radius Rl of the connection tank part 40 is the length of the line segment JE. Further, the junction point G between the lower tank part 30 and the connection tank part 40 is located such that the junction point G is vertically symmetrical to the junction point E with respect to the line segment AB, which is the center line of the connection tank part 40. Thus, at the junction point G, the tangential gradients 80 of both the lower tank part 30 and the connection tank part 40 are equal to each other.

As shown in the drawing, the section of the LNG storage tank 10 further comprises two junction points F and H, which are located such that the junction point F is horizontally symmetrical to the junction point E with respect to a line segment CD, which is the central axis of the LNG storage tank 10, and the junction point H is vertically symmetrical to the junction point F with respect to the line segment AB, which is the horizontal center line of the connection tank part 40.

In other words, the upper tank part 20 of the extended spherical LNG storage tank 10 is defined by the circular arc EF (radius of curvature R) , the lower tank part 30 is defined by the circular arc GH (radius of curvature R) , the connection tank part 40 is defined both by the circular arc EG (radius of curvature Rl) and by the circular arc FH (radius of curvature Rl) , and the extended spherical LNG storage tank 10 is defined by the combination of the above-mentioned circular arcs. Further, at the junction points E, F, G and H, at which the circular arcs are joined together, the tangential gradients of the circular arcs are equal to each other. FIG. 7 is a diagram illustrating the concept of the extension structure of the LNG storage tank according to a second embodiment of the present invention. As shown in the drawing, the connection tank part 40 is defined by a parabola, which has both a start point at a point S on the circular arc of the upper tank part 20 and an end point at a point U on the circular arc of the lower tank part 30, wherein the start point S and the end point U are vertically symmetrical on the basis of the horizontal center line of the connection tank part 40. Described in detail, the connection tank part 40 is defined by a parabola that is defined by a quadratic equation, so that the tangential gradients 80 of the parabola at both the start point S and the end point U are equal to the tangential gradients 80 of the upper tank part 20 and the lower tank part 30 at the same points. Further, the center line of the parabola is defined by a line segment AB.

In the second embodiment, the tangential gradients 80 at the junction points between the circular arcs of the upper and lower tank parts and the parabola of the connection tank part are equal to each other. Thus, the connection tank part 40 can be smoothly joined both to the upper tank part 20 and to the lower tank part 30, thus increasing the LNG storage capacity of the LNG storage tank 10 and mitigating the stress concentration on the connection tank part 40, thereby improving the safety of the LNG storage tank.

Further, the support skirt 50, which supports the extended spherical LNG storage tank 10 on the deck of the LNG tanker, is preferably mounted around the equatorial part 45 of the connection tank part 40, so that, when the skirt 50 is securely installed on the deck of the LNG tanker, the skirt 50 safely and stably supports the LNG storage tank 10 on the deck of the LNG tanker.

FIG. 8 is a perspective view illustrating a connection tank part according to an embodiment of the present invention. FIG. 9 is a front view illustrating the connection tank part according to the embodiment of the present invention, which is integrated with an LNG storage tank.

As shown in the drawings, the connection tank part 40 is produced by integrating a plurality of plates 44 into a single structure, wherein the longitudinally joined parts of the plates 44 are located along the circular arc or the parabola C3, which defines the connection tank part 40.

If the longitudinally joined parts of the plates 44 are located outside the circular arc or the parabola C3, stress may be concentrated on the longitudinally joined parts of the plates 44 in the connection tank part 40. The connection tank part 40 comprises a first connection unit 41 and a second connection unit 42, which are placed at upper and lower locations in the connection tank part 40, respectively, and an equatorial part 45, which is assembled with a lower part of the second connection unit 42 and supports a support skirt 50 therearound.

The first connection unit 41 is produced by the combination of a plurality of plates 44 such that the first connection unit 41 has a trapezoidal section, the lower side being longer than the upper side. The upper end of the first connection unit 41 is integrated with the lower end of the upper tank part 20. The second connection unit 42 is produced by the combination of a plurality of plates 44 such that the second connection unit 42 has a trapezoidal section, the upper side being longer than the lower side. The upper end of the second connection unit 42 is integrated with the lower end of the first connection unit 41. The equatorial part 45 is produced by the combination of a plurality of plates 44 such that the upper end of the equatorial part 45 has a circumference corresponding to the lower end of the second connection unit 42 and the lower end of the equatorial part 45 has a circumference corresponding to the upper end of the lower tank part 30. The upper end of the equatorial part 45 is integrated with the lower end of the second connection unit 42, while the lower end of the equatorial part 45 is integrated with the upper end of the lower tank part 30.

Here, each of the plates 44 of the first connection unit 41 and the second connection unit 42 is configured as a trapezoidal plate 44a having a truncated sectorial shape and a curved surface. The curved trapezoidal plates 44a are integrated with each other into a single structure at the left and right sides thereof through welding, so that each of the first and second connection units 41 and 42 has a circular truncated conical shape having a trapezoidal cross-section.

During a process of producing the connection tank part 40 according to the embodiment of the present invention, the trapezoidal plates 44a, each having a two-dimensional curved surface, are assembled with each other, thus easily forming the first connection unit 41 and the second connection unit 42. Because each of the first connection unit 41 and the second connection unit 42 has a trapezoidal cross-section, the extended spherical LNG storage tank according to the embodiment of the present invention has a larger LNG storage capacity than to the conventional cylinder-inserted LNG storage tank. Further, because the first and second connection units 41 and 42 are smoothly connected to the upper and lower tank parts 20 and 30, respectively, it is possible to mitigate the stress concentration on the connection tank part 40.

FIG. 10 is a perspective view illustrating the connection tank part according to another embodiment of the present invention. FIG. 11 is a front view illustrating the connection tank part according to the embodiment of the present invention, which is integrated with an LNG storage tank.

As shown in the drawings, the connection tank part 40 is produced by the integration of a plurality of plates 44 into a single structure, wherein the longitudinally joined parts of the plates 44 are located along the circular arc or the parabola C3, which defines the connection tank part 40.

The connection tank part 40 comprises a first connection unit 41, a second connection unit 42 and a third connection unit 43, which are placed at upper, lower and middle locations in the connection tank part 40, respectively, and an equatorial part 45, which is assembled with the lower part of the second connection unit 42 and has a support skirt therearound.

The first connection unit 41 is produced by the lateral combination of a plurality of plates 44 such that the first connection unit 41 has a trapezoidal section, the lower side being longer than the upper side. The upper end of the first connection unit 41 is integrated with the lower end of the upper tank part 20.

The third connection unit 43 is produced by the combination of a plurality of plates 44 such that the upper end of the third connection unit 43 has a circumference corresponding to the lower end of the first connection unit 41 and the lower end of the third connection unit 43 has a circumference corresponding to the upper end of the second connection unit 42. The upper and lower ends of the third connection unit 43 are integrated with the first and second connection units 41 and 42, respectively.

The second connection unit 42 is produced by the lateral combination of a plurality of plates 44 such that the second connection unit 42 has a trapezoidal section, the upper side being longer than the lower side. The upper end of the second connection unit 42 is integrated with the lower end of the third connection unit 43.

The equatorial part 45 is produced by the combination of a plurality of plates such that the upper end of the equatorial part 45 has a circumference corresponding to the lower end of the second connection unit 42 and the lower end of the equatorial part 45 has a circumference corresponding to the upper end of the lower tank part 30. The upper end of the equatorial part 45 is integrated with the lower end of the second connection unit 42, while the lower end of the equatorial part 45 is integrated with the upper end of the lower tank part 30.

Here, each of the plates 44 of the first connection unit 41 and the second connection unit 42 is configured as a trapezoidal plate 44a. The trapezoidal plates 44a are first subjected to a bending process to curve them. Thereafter, the curved trapezoidal plates 44a are laterally integrated with each other into a single structure at their left and right sides through welding, so that each of the first and second connection units 41 and 42 has a circular truncated conical shape. Thus, the first and second connection units 41 and 42 can be smoothly connected to the upper and lower tank parts 20 and 30, respectively, so that it is possible to mitigate the stress concentration on the connection tank part 40.

Further, the plates 44 of the third connection unit 43 are rectangular plates 44b, which are subjected to a bending process. The curved rectangular plates 44b are laterally welded together at left and right sides thereof to form the third connection unit 43.

FIG. 12 is a diagram illustrating variation in the thickness of the connection tank part according to the present invention. As shown in FIG. 12, the connection tank part 40 according to the embodiment of the present invention has a thickness which is increased in a downward direction.

Because the thickness of the connection tank part is increased in the downward direction in consideration of structural analysis analyzing the effect on the structure of the tank according to the weight of the tank and the LNG charged in the tank, and according to the additional load attributable to rolling and sloshing during the transportation of LNG, it is possible to secure safety of the LNG storage tank. FIG. 13 is a diagram illustrating the results of structural strength analysis of the connection tank part according to the present invention. This diagram shows the results of structural strength analysis for analyzing the variation in the structural strength of the LNG storage tank according to the dynamic acceleration of LNG charged in the storage tank, the weight of the LNG and the storage tank, and the thermal stress.

Here, (a) of FIG. 13 shows the results of structural strength analysis for a connection tank part having a conventional cylindrical structure (maximum 150 MPa) , (b) of FIG. 13 shows the results of structural strength analysis for a connection tank part having a cylindrical structure with the thickness increased in the downward direction (maximum 81 MPa) , and (c) of FIG. 13 shows the results of structural strength analysis for the connection tank part 40 according to the present invention (maximum 79 MPa) . As shown in the drawings, the stress concentration on the connection tank part is determined as a>b>c.

The structural strength analysis for the connection tank part shows that, when the upper tank part 20 and the lower tank part 30 of the connection tank part 40 are assembled with each other at a gentle angle and the thickness of the connection tank part 40 is increased in the downward direction, as described above for the present invention, it is possible to mitigate stress concentration on the connection tank part and safely use the LNG storage tank. FIG. 14 is a diagram illustrating the structure for mounting the support skirt according to the present invention.

The support skirt 50 is preferably installed around the lower part of the second connection unit 42 so as to provide space for welding work. FIG. 15 is a diagram illustrating a process for producing a plate, which constitutes the upper tank part and the lower tank part of the present invention. FIG. 16 is a diagram illustrating a process for producing the vertex of each of the upper and lower tank parts of the present invention. FIG. 17 is a diagram illustrating a process for producing the connection tank part according to an embodiment of the present invention. FIG. 18 is a diagram illustrating a process for producing the connection tank part according to another embodiment of the present invention. As shown in the drawings, to produce an extended spherical LNG storage tank 10 according to the present invention, a plurality of plates 44 is integrated together to form an upper tank part 20 and a lower tank part 30. Further, a plurality of plates 44 is integrated together to form a connection tank part 40, which has a radius of curvature larger than that of each of the upper and lower tank parts 20 and 30. Further, a support skirt 50, which is to be mounted to the connection tank part 40 and is to be securely installed on the deck of the LNG tanker, is produced. Thereafter, the connection tank part 40 is integrated with the upper end of the lower tank part 30, and a pipe tower 60 is vertically installed on the center of the lower tank part 30. The support skirt 50 is installed around the circumference of the connection tank part 40. Thereafter, the upper tank part 20 is integrated with the upper end of the connection tank part 40 such that the upper end of the pipe tower 60 is connected to the upper end of the upper tank part 20.

The upper tank part 20 is produced by integrating a plurality of upper tank sub-assemblies 21 into a single structure and by integrating the upper end of the single structure, formed by the integration of the upper tank sub- assemblies 21, with a vertex 22, which has the same radius of curvature as that of each of the upper tank sub-assemblies 21. Here, to produce each of the upper tank sub-assemblies 21, trapezoidal plates 48, each having a truncated sectorial shape and being bent through a bending process to have a curved surface, are laterally integrated with each other, thus forming an upper tank sub-assembly 21 having a circular truncated conical shape with a trapezoidal cross-section, wherein the lower side is longer than the upper side.

Further, the lower tank part 30 is produced by integrating a plurality of lower tank sub-assemblies 31 into a single structure and by integrating the lower end of the single structure, formed by the integration of the lower tank sub- assemblies 31, with a vertex 22, which has the same radius of curvature as that of each of the lower tank sub-assemblies 31. Here, to produce each of the lower tank sub-assemblies 31, a plurality of trapezoidal plates 48, each having a truncated sectorial shape and being bent through a bending process to have a curved surface, is laterally integrated with each other, thus forming a lower tank sub-assembly 31 having a circular truncated conical shape with a trapezoidal cross-section, wherein the upper side is longer than the lower side. As shown FIG. 17, to produce the connection tank part 40, the trapezoidal plate 44a that constitutes the second connection unit 42 is integrated with the lower end of the trapezoidal plate 44a that constitutes the first connection unit 41. Further, a plate, which constitutes the equatorial part 45 for supporting the support skirt 50, is vertically integrated with the lower end of the trapezoidal plate 44a, which constitutes the second connection unit 42, so that a first connection tank sub-assembly 46 is produced. When a plurality of first connection tank sub-assemblies 46 is completely produced in the same manner as that described above, the first connection tank sub-assemblies 46 are laterally integrated with each other to form a single structure through welding.

Further, as shown in FIG. 18, to produce the connection tank part 40, a rectangular plate 44b, which constitutes the third connection unit 43, is vertically integrated with the lower end of a trapezoidal plate 44a, which constitutes the first connection unit 41. Further, a trapezoidal plate 44a, which constitutes the second connection unit 42 and corresponds to the trapezoidal plate 44a of the first connection unit 41, is integrated with the lower end of the rectangular plate 44b of the third connection unit 43. Thereafter, a plate, which constitutes the equatorial part 45 for supporting the support skirt 50, is vertically integrated with the lower end of the trapezoidal plate 44a of the second connection unit 42, thus forming a second connection tank sub-assembly 47. When a plurality of second connection tank sub-assemblies 47 is completely produced in the same manner as that described above, the second connection tank sub-assemblies 47 are laterally integrated with each other into a single structure through welding. FIG. 19 is a diagram illustrating a process of producing the LNG storage tank according to the present invention. As shown in the drawing, a connection tank part 40 is mounted to the upper end of a lower tank part 30, which was produced in advance and is placed in a dock. Thereafter, a pipe tower 60 is vertically installed at the center of the lower tank part 30. A support skirt 50 is installed around the circumference of the connection tank part 40. Thereafter, an upper tank part 20 is integrated with the upper end of the connection tank part 40 such that the upper end of the pipe tower 60 is connected to the upper end of the upper tank part 20, thus producing an LNG storage tank according to the present invention. While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modification may be made without departing from the spirit and scope of the invention as defined in the following claims . [Advantageous Effects]

The present invention, which has the above-mentioned construction and operation, is advantageous in that the junctions between the connection tank part and the upper and lower tank parts are configured as smooth parts, and the thickness of the connection tank part is gradually increased in a direction toward the lower part thereof, thus mitigating stress concentration on the connection tank part and effectively increasing the LNG storage capacity of the tank. Further, the connection tank part is constructed by welding a plurality of plates to each other to form a single structure, thus increasing work efficiency when fabricating the connection tank part.

[Description of Drawings] FIG. 1 is a view illustrating the arrangement of conventional spherical LNG storage tanks on an LNG tanker and the line of vision of a helmsman of the LNG tanker;

FIG. 2 is a view illustrating an LNG tanker equipped with conventional cylinder-inserted LNG storage tanks;

FIG. 3 is a view illustrating one of the conventional cylinder-inserted LNG storage tanks;

FIG. 4 is a view illustrating an extended spherical LNG storage tank according to the present invention;

FIG. 5 is a diagram illustrating the concept of a connection tank part of the LNG storage tank according to the present invention;

FIG. 6 is a diagram illustrating the concept of the extension structure of the LNG storage tank according to a first embodiment of the present invention;

FIG. 7 is a diagram illustrating the concept of the extension structure of the LNG storage tank according to a second embodiment of the present invention; FIG. 8 is a perspective view illustrating a connection tank part according to an embodiment of the present invention;

FIG. 9 is a front view illustrating the connection tank part according to the embodiment of the present invention, which is integrated with an LNG storage tank; FIG. 10 is a perspective view illustrating a connection tank part according to another embodiment of the present invention;

FIG. 11 is a front view illustrating the connection tank part according to the embodiment of the present invention, which is integrated with an LNG storage tank;

FIG. 12 is a diagram illustrating variation in the thickness of the connection tank part according to the present invention;

FIG. 13 is a diagram illustrating the results of structural strength analysis of the connection tank part according to the present invention; FIG. 14 is a diagram illustrating the structure for mounting a support skirt according to the present invention;

FIG. 15 is a diagram illustrating a process for producing a plate, which constitutes an upper tank part and a lower tank part of the present invention; FIG. 16 is a diagram illustrating a process for producing a vertex of each of the upper and lower tank parts of the present invention;

FIG. 17 is a diagram illustrating a process for producing the connection tank part according to an embodiment of the present invention;

FIG. 18 is a diagram illustrating a process for producing the connection tank part according to another embodiment of the present invention; and

FIG. 19 is a diagram illustrating a process of producing the LNG storage tank according to the present invention.

10: extended spherical LNG storage tank

11: cylinder-inserted LNG storage tank

20: upper tank part 21: upper tank sub-assembly

22: vertex 30: lower tank part

31: lower tank sub-assembly 40: connection tank part 40a: cylindrical connection tank part

41: first connection unit 42: second connection unit

43: third connection unit 44, 48: plates

44a: trapezoidal plates

44b: rectangular plates 45: equatorial part

46: first connection tank sub-assembly

47: second connection tank sub-assembly

50: support skirt 60: pipe tower

70: dock 80: tangential gradient

100: LNG tanker 101: pilot house

102: visual range 103: line of vision

Claims

[CLAIMS]

[Claim 1]

An extended spherical LNG storage tank, comprising an upper tank part and a lower tank part, each having a predetermined radius of curvature R, and a connection tank part provided between the upper tank part and the lower tank part so as to increase LNG storage capacity of the LNG storage tank, wherein the connection tank part is defined by a circular arc or a parabola C3, which is circumscribed with two circles Cl and C2 that define the upper tank part and the lower tank part, respectively, outside the two circles Cl and C2.

[Claim 2]

The extended spherical LNG storage tank according to claim 1, wherein the connection tank part is defined by a circular arc having a start point and an end point at respective crossing points, at which lines, extending from a point on a center line that horizontally passes through a center of the connection tank part and passing through centers of curvature of the upper and lower tank parts, cross the circular arcs of the upper and lower tank parts, respectively, the circular arc of the connection tank part having a radius of curvature Rl defined by a distance from the point on the center line of the connection tank part to each of the crossing points.

[Claim 3]

The extended spherical LNG storage tank according to claim 1, wherein the connection tank part is defined by a parabola C3 having a start point at a point on the circular arc of the upper tank part and having an end point at a point on the circular arc of the lower tank part, wherein the start point and the end point are symmetrical to each other and tangential gradients of the parabola at the start and end points are equal to tangential gradients of the upper and lower tank parts at the start and end points .

[Claim 4]

The extended spherical LNG storage tank according to any one of claims 1 through 3, wherein the connection tank part is fabricated by integrating a plurality of plates into a single structure.

[Claim 5]

The extended spherical LNG storage tank according to claim 4, wherein the connection tank part comprises: a first connection unit and a second connection unit, which are placed at upper and lower locations in the connection tank part, respectively, and an equatorial part assembled with a lower part of the second connection unit and supporting a support skirt therearound.

[Claim 6]

The extended spherical LNG storage tank according to claim 4, wherein the connection tank part comprises: a first connection unit, a second connection unit and a third connection unit, which are placed at upper, lower and middle locations in the connection tank part, respectively, and an equatorial part assembled with a lower part of the second connection unit and supporting a support skirt therearound.

[Claim 7]

The extended spherical LNG storage tank according to claim 5 or 6, wherein each of the first connection unit and the second connection unit has a circular truncated conical shape.

[Claim 8]

The extended spherical LNG storage tank according to claim 1, wherein the connection tank part has a thickness which is increased in a downward direction. [Claim 9]

A method for manufacturing an extended spherical LNG storage tank, comprising: producing each of an upper tank part and a lower tank part by assembling a plurality of plates into a single structure; producing a connection tank part, having a radius of curvature larger than that of each of the upper and lower tank parts, by assembling a plurality of plates into a single structure; producing a support skirt, the support skirt being mounted to the connection tank part and securely installed on a deck of an LNG tanker so as to support the LNG storage tank on the deck; and mounting the connection tank part on a top of the lower tank part, vertically installing a pipe tower on a center of the lower tank part, mounting the support skirt around a circumference of the connection tank part, and mounting the upper tank part on a top of the connection tank part such that a top of the upper tank part is connected to the pipe tower.