Double Wall Corrugated Lng Tank

Abstract

A double wall tank for the marine transportation of liquefied natural gases at atmospheric pressure and cryogenic temperature, the tank having its primary and secondary barriers supported in such a way that the respective barrier supports are in alignment. The walls of the inventive tank, in its preferred embodiment, are corrugated in a horizontal direction. All liquid-tight welds are either butt or seam welds, and all transitions between the walls of the tank are smooth, without intermediate box girders. A plurality of vertical webs support the primary barrier of the tank; and a plurality of diaphragms, intermediate the primary and secondary barriers, are positioned in alignment with the vertical webs and support the secondary barrier. The vertical webs are stabilized by lightweight channel-shaped struts; corner plates support the corners of the tank and serve as base members for the struts. The tank is supported and keyed at the bottom only, thereby reducing the load transmitted to the structure of the ship near the top of the tank.

Description

BACKGROUND OF THE INVENTION

In copending U.S. patent application Ser. No. 732,009, now U.S. Pat. No. 3,670,517, a streamlined continuation of its parent application filed on Mar. 16, 1965, assigned to the present assignee, a double wall corrugated tank for the marine transportation of liquefied natural gases is disclosed. In this patent application the corrugations in the side walls of the tank are vertically oriented while the corrugations in the top and bottom walls of the tank are horizontally oriented. Four box girders are provided at the top of the tank and four similar box girders are provided at the bottom of the tank. The top, bottom and side walls of the tank, with their corrugations, are T-welded to the respective box girders. The walls of the tank are supported and stabilized by internal vertical webs, between-wall diaphragms and horizontal stringers.

Because of its design, the tank disclosed in the above-noted copending patent application has numerous drawbacks. First, since a large number of T-welds appear both in the primary and secondary barriers, liquid-tight construction becomes a difficult task. The T-weld is not easily made liquid-tight; and a radiographic leak detection procedure is correspondingly difficult. In addition, the T-welds result in local points of stress concentration. And, further, the need for box girder systems adds both to the weight and the cost of the cargo tank.

In this copending patent application, the secondary barrier of the disclosed tank is supported by a plurality of diaphragm plates; and the primary barrier is supported by a number of vertical webs. To stabilize the vertical webs, a plurality of horizontal stringers is provided. This construction, while effective, tends to be overly complex and, because of its complexity, tends to be somewhat heavy.

In many of the tanks known to the prior art, the supporting function and the keying function are performed by distinct structures. Further, the tanks are often supported at a number of positions around its periphery. Such arrangements, it has been found, tend to be somewhat uneconomical and overly complex. In addition, it has been found that the tank loads have often been transmitted to the structure of the ship near the top of the tank, thereby causing stress in the ship structure.

It is toward the elimination of the above-noted drawbacks which exist in the tanks known to the prior art that the present invention is directed.

SUMMARY OF THE INVENTION

The present invention relates to a double wall tank for the marine transportation of liquefied natural gases at atmospheric pressure and cryogenic temperature. The inventive tank is corrugated throughout, and has many economic advantages over those tanks known to the prior art.

With the corrugated tank of the present invention, smooth transitions between tank walls are provided. In this manner, all T-welds and each of the problems associated therewith are avoided. The elements of the inventive tank, both in the primary and secondary barriers, are either butt welded or are seam welded. Therefore, the welds may more easily be made liquid-tight. And, because of the smooth transitions without T-welds, the conventional points of high stress concentration have been eliminated. Further, butt and seam welds may readily be checked for liquid-tight operation by the use of radiographic techniques; as noted above, radiographic analysis is quite difficult with T-welds. In the preferred embodiment of the inventive tank, all of the walls have their corrugations aligned in the horizontal direction.

In the horizontally corrugated embodiment of the double wall tank forming a part of the present invention, the primary barrier is supported by a plurality of vertical webs located within the primary barrier. Diaphragms are positioned intermediate the primary and secondary barriers, and in alignment with the vertical support the secondary barrier. With the vertical webs and the diaphragms so aligned, the need for horizontal stringers is eliminated. As a result, there is a large potential weight savings. However, to ensure proper stabilization of the inner flanges of the vertical webs, relatively lightweight channel-shaped struts are provided. But even with these struts, there is a substantial savings in weight when comparing the tank of the present invention with the tank disclosed in the above-referenced copending patent application.

While the corrugations are preferably aligned horizontally, the present invention contemplates that they may be vertically aligned as well. Then, rather than using vertical webs as the primary support members, horizontal stringers would be used. The present invention then involves aligning the diaphragm plates horizontally with the horizontal stringers.

The inventive tank is supported and keyed in place from the bottom only. This, in comparing the inventive tank with tanks known to the prior art, is quite simple in design and greatly reduces the loads introduced into the structure of the ship near the top of the tank.

In a first embodiment, the tank of the present invention has enlarged rounded corners providing access between the primary and secondary barriers. This access facilitates inspection and repair of the two liquid-tight barriers. In a second embodiment, the space between the primary and secondary barriers is large enough to provide access in a direction perpendicular to the horizontal corrugations. This second embodiment, while decreasing the carrying capacity of the tank, may be found to be more economical in the end due to the ease of construction gained by such a configuration and the ease with which inspection may be accomplished.

Accordingly, it is the main object of the present invention to provide a double wall tank for the marine transportation of liquefied natural gases at atmospheric pressure and cryogenic temperature, which tank is constructed with relative ease, which is light in weight, and which is quite strong.

Another object of the invention is to provide a double wall cargo tank whose weight is reduced by the elimination of the need for heavy support and stabilization members.

Still another object of the invention is to provide a double wall cargo tank whose support and stabilization members are in alignment, thereby enhancing the effects of these members.

Yet a further object of the invention is to provide a double wall corrugated cargo tank having smooth between-wall transitions and eliminating the need for T-welds.

Yet another object of the present invention is to provide a double wall corrugated tank having maximum strength with a minimum number of structural elements.

A further object of the present invention is to provide a double wall corrugated tank requiring no horizontal stringers for purposes of strength.

Still a further object of the present invention is to provide a corrugated tank which is supported and keyed on the bottom only.

Another object of the present invention is to provide a double wall corrugated tank wherein ready access is provided between the walls of the tank.

A further object of the present invention is to provide a double wall corrugated tank wherein access between the walls tank is provided in a direction parallel to the corrugations.

Still another object of the present invention is to provide a double wall corrugated tank wherein access is provided between the walls of the tank in a direction transverse to the corrugation.

Yet a further object of the present invention is to provide a horizontally corrugated cargo tank having the qualities recited above.

These and other objects of the present invention, as well as many of the attendant advantages thereof, will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation, partially in section, of a ship equipped with a cargo tank constructed in accordance with the teachings of the present invention;

FIG. 2 is a vertical cross-section of the inventive tank taken along line 2--2 of FIG. 3;

FIG. 3 is a horizontal cross-section of the inventive tank taken along line 3--3 of FIG. 2;

FIG. 4 is a cross-section of the inventive tank taken along line 4--4 of FIG. 3;

FIG. 5 is a cross-section taken along line 5--5 of FIG. 3;

FIG. 6 is a cross-section of a corrugated wall of the inventive tank taken along line 6--6 of FIG. 5;

FIG. 7 is a cross-section taken along line 7--7 of FIG. 6;

FIG. 8(a) is a cross-section showing the top and side wall corrugations;

FIG. 8(b) is a cross-section showing the deeper tank bottom corrugations;

FIG. 9 is a cross-section through line 9--9 of FIG. 2; and

FIG. 10 is a perspective view showing the corner construction of the inventive tank.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference first to FIG. 1, a ship equipped with a plurality of cargo tanks constructed in accordance with the teachings of the present invention is shown generally at 10 with a portion of the hull 12 cut away to expose a number of cargo tanks 14 (only two being shown). As is customary in the field of marine transportation of cryogenic fluids, it is contemplated that a large number of cargo tanks be provided in the holds of the ship 10. The tanks 14 are located below the deck 16 of the ship 10 and are entirely surrounded by a layer of insulation 18, this insulation, for example, taking the form of a number of foam blocks. As shown in FIG. 1, the layer of insulation 18 is affixed to the outer wall of the tanks 14; however, this insulation may be affixed to the inner hull of the ship or spaced between the inner hull of the ship and the outer wall of the tank.

The ship 10 is of the double hull variety, as seen in FIG. 3, the hull 12 being defined by an outer hull 20 and an inner hull 22. And, as seen in FIG. 1, the bottom of the ship is defined by an outer bottom 24 and an inner bottom 26. Between the inner bottom 26 of the ship 10 and the bottom of the tank 14, a plurality of keying and foundation members 28 are illustrated. Anti-floatation chocks 30, located between transverse bulkheads 32 and the tanks 14, harness the upward movement of the tanks 14 in the event that the cargo hold should flood.

Now, with particular reference to FIGS. 2 through 4, the construction of an embodiment of the inventive tank will be described. The cargo tank 14, as noted above, is of the double wall variety. The primary barrier, or internal wall, is represented at 34 and the secondary barrier, or external wall, is represented at 36. The tank has a bottom 38, a top 40, a pair of internal sides 42 and 44, respectively, adjacent the transverse bulkheads 32, and a pair of external sides, only one being shown at 46, adjacent the inner hull 22. As is evident from the figures, both the internal wall 34 and the external wall 36 of the tank 14 are corrugated, and are corrugated in the horizontal direction.

A corrugated longitudinal liquid-tight bulkhead 48 extends the entire distance between and supports the inner sides 42 and 44 of the tank 14, and a corrugated transverse swash bulkhead 50 extends between and supports the outer sides of the tank 14. In this manner, the longitudinal liquid-tight bulkhead 48 and the transverse swash bulkhead 50 divide the tank 14 into four substantially equal volumes.

A number of vertical webs 52, positioned both in the longitudinal and transverse directions, extend into the body of the tank 14 and serve to support the primary barrier or internal wall 34 thereof. A number of vertically oriented diaphragms 54 are welded both to the inner wall 34 and the outer wall 36, are positioned in alignment with the vertical webs 52 and support the secondary barrier 36.

In the described embodiment of the inventive tank, with the corrugations oriented in the horizontal direction and with the vertical webs positioned in alignment with the vertical diaphragms, the horizontal stringers required in the cargo tank disclosed in the above-noted copending U.S. patent application become unnecessary. In the copending patent application, with the side wall corrugations oriented in a vertical direction, and with the vertical webs and diaphragms positioned as there shown, the vertical webs and diaphragms did little to stabilize the tank in the horizontal direction. With the side walls of the tank corrugated in a horizontal direction, and with the webs and diaphragms aligned, on the other hand, as in the presently described tank, horizontal stabilization is inherent. Therefore, the customary horizontal stringers may be eliminated, the construction of the described horizontally corrugated cargo tank is less complex than that associated with the vertically corrugated cargo tanks known to the prior art and, as a consequence, the weight of the inventive tank is less than the weight of the known tanks.

As noted in the preceding paragraph, the horizontal corrugations and the alignment of the webs and diaphragms in the cargo tank described and illustrated herein eliminate the need for heavy horizontal stringers. However, even with the inventive tank, the innermost flanges of the vertical webs must be stabilized. As shown in the figures, these flanges are stabilized by a plurality of horizontal channel-shaped struts 56. Since the horizontal stringers disclosed in the above-referenced copending U.S. application serve the function of stabilizing the tank walls in a horizontal direction, and since the struts 56 serve only the function of stabilizing the vertical webs, it should be evident that the strength of the struts 56 need not be as great as the strength of the horizontal stringers required in the prior art tanks. Therefore, the horizontally corrugated cargo tank forming a part of the present invention is lighter in weight than the cargo tanks known to the prior art.

In FIGS. 3, 5, 6 and 7, the areas of intersection between the vertical webs and the longitudinal and transverse bulkheads are shown. First, it should be noted that the innermost regions of the vertical webs are provided with flanges 58, these flanges serving as stays for preventing excessive deflexion in their associated webs 52. It is the flanges, or stays which support the U-shaped channels 56.

The vertical webs 52, in the areas of intersection with the corrugated bulkheads 48 and 50, are broken and are welded to the respective bulkheads. Horizontal triangular plating members 60 are welded to the bulkheads 48 and 50, to the vertical webs 52 and to the flanges 58 extending from the vertical webs. As seen in FIGS. 2 and 3, the triangular plating members 60 are spaced, in a vertical direction, along the bulkheads 48 and 50.

The elements of the inventive tank are further stabilized by a series of horizontally oriented plating members located at critical areas in the tank. As seen in FIG. 3, these support members take the form of mid-tank plating elements 62 stabilizing the bulkheads 48 and 50 at their line of intersection, corner plating elements 64 stabilizing the tank at its corners, and side plating elements 66 serving to stabilize the bulkheads 48 and 50 at the lines of intersection with the sides of the tank.

As seen in FIGS. 5 through 7, the transverse swash bulkhead 50 is provided with a set of bulkhead openings 70, these openings reducing the undesirable splashing of the cargo during the voyage of the ship. The longitudinal bulkhead 48 may, if desired, be provided with a set of openings aligned and positioned so as to provide roll stabilization for the ship when the tanks are charged with cargo.

As seen in FIGS. 4 and 8, the diaphragms 54 are also provided with openings, these being shown at 72, positioned at the widest regions between the corrugations defining the inner and outer walls of the tank. The openings 72 are important in that they provide means for physical communication between areas defined by the diaphragms 54. If the openings were not provided, there would be no available access for purposes of inspecting the primary and secondary barriers of the tank.

Additional strength is provided by a plurality of longitudinal girders 74 extending along the tank 14 and welded to the bottom wall thereof. The function of the girders 74 is to transmit foundation loads into the tank structure.

Now, with reference to FIGS. 1 through 4, the support and alignment of the tank 14 will be explained. As noted previously, the tank 14 is provided with anti-floatation chocks 30 serving to prevent the tank from rising in its hold in the event that the hold should flood. As seen in the figures, each anti-floatation chock 30 is defined by a flange 76 attached to and extending from the respective side wall of the tank 14, and a flange 78, aligned with the flange 76, welded to the respective liquid-tight bulkhead 32 defining the cargo holds. As seen best in FIG. 2, a small space is provided between the flanges 76 and 78, this space preventing contact between the elements of the anti-floatation chocks 30 under all conditions save for hold flooding. The chocks 30 in no way add to the support of the tank 14.

As is evident from the figures, the tank is supported only at its bottom, the tank-supporting structures serving also as keying elements. With more particular reference to FIGS. 2 and 4, the combination keying and supporting elements will be described. A number of pedestals 80 are fixedly attached to the inner bottom 26 of the ship. And, adapted to associate with the pedestals 80, a number of wooden insulating blocks 82, as of balsa or fir, are attached to the outer wall 36 of the tank 14, at the bottom thereof. The combination of the pedestals 80 and the insulating blocks 82 make up tank foundations which transmit the loads exerted by the tank to the structure of the ship. Due to the extreme temperature changes experienced by the tank, with its resulting contractions and expansions, the pedestals 80 and the insulating blocks 82 are associated in such a manner so as to allow sliding contact therebetween.

It is important that the cargo tanks remain in relatively fixed positions within their respective holds. Naturally, because of the contractions and expansions experienced by the cargo tanks, they must be fixed in a special manner. In the inventive tank, three lines of foundations are provided. Two lines are provided at the tank bottom near the hull of the ship, and the third line of foundation is provided along the center line of the ship, each line of foundation being oriented in a longitudinal direction. These foundations ensure that the tanks are held relatively fixed within their respective holds, allowing, of course, for expansion and contraction.

As seen most clearly in FIG. 4, a keying arrangement is provided at the central region of the tank. This keying arrangement takes the form of a number of transverse keys 84 rigidly secured to the inner bottom 26 of the ship and a number of transverse keys 86 rigidly secured to the outer wall 36 of the tank 14. As seen in this figure, the directions of the transverse keys are made to alternate. In this manner, the insulation block 82 serves the dual function of insulating the tank 14 from the hull of the ship and also insulating the tank keys 86 from the ship keys 84. For a full disclosure of this keying arrangement the attention of the reader is directed to U.S. Pat. No. 3,428,205, issued Feb. 18, 1969, and assigned to the present assignee.

As will be readily apparent when viewing FIGS. 2, 3 and 4, there are three types of transitions between the sides, top and bottom of the cargo tank 14; and each of these transitions is done smoothly without the necessity for complex and heavy box girder structures. The first type of corner transition is illustrated in FIG. 2 and is indicated generally at 88; the second corner transition is illustrated in FIG. 3 and is indicated generally at 90; and the third is illustrated in FIG. 4 and is indicated generally at 92.

With reference first, to FIG. 2, the corner transition 88 will be explained. This transition 88 may conveniently be termed a T transition. Here, the horizontal corrugations in the side walls are perpendicular to the horizontal corrugations in the top and bottom walls. In this case, the transition between the side walls and the top and bottom walls is made by abruptly ending the side wall corrugations at the widest region thereof and by terminating the top and bottom corrugations by smoothly tapering these corrugations into flat plates spaced apart by the maximum distance between the corrugations. From FIG. 2, it can be seen that the smooth corner transitions require no T-welds or box girder structures. Further, because of the smoothness of the transition, local areas of extreme stress are avoided.

In FIG. 3, the second type of corner transition, transition 90, will be explained. Transition 90 may be termed an L transition. Here, while the side all corrugations are perpendicular to the top and bottom wall corrugations, an L is defined at the intersection. This transition is developed, both at the top and bottom walls, by smoothly tapering both sets of corrugations into flat plates spaced apart by a distance equal to a maximum corrugation spacing. Again, the transition is made smoothly, thus avoiding the necessity for box girders and T-welds and eliminating localized stress concentration.

In FIG. 4, the last type of corner transition, indicated at 92, is illustrated. This type of corner transition 92 may be termed a "parallel" transition, for the side wall corrugations are parallel to the top and bottom wall corrugations. Here, the mating is carried out by abruptly ending the corrugations in the side walls, the top and the bottom, at the region where the distance between the outer and inner walls of the tank are maximum, the corners being defined by smoothly curved plates. Again the corner is defined without the use of box girders, without T-welds and without areas of local stress concentration.

In FIG. 10, a typical corner transition is illustrated in perspective. Here, it can be seen that the transition is smooth and that it is designed so that the maximum distance between the corrugated tank walls is utilized. The construction of the corner is as follows.

Corrugation transition pieces 100 are fit on each of the corrugated walls and are designed to gradually taper the corrugations to a flat plate. The transition pieces 100 are welded to their respective corrugated walls by a butt weld, seen at 102. The two transition pieces 100 are then butt welded to a vertical arcuate corner piece 104, and the vertical transition is completed. The remaining portions of the corner transition illustrated in FIG. 10 are completed by similarly joining the tank top to its adjacent tank side walls by means of horizontal arcuate corner pieces 106 and by fitting the one eighth spherical corner piece 108 between the respective corner pieces 104 and 106.

From the above description of the three types of corner transitions, the advantages of the inventive corrugated tank should be clear. With the smooth transitions described above, the standard box girder structures are eliminated. This results both in weight savings and cost savings. And, because the transitions are smooth, rather than abrupt, all T-welds are avoided, these being replaced by butt welds or seam welds. As noted previously, butt and seam welds are less difficult to perfect than are T-welds, and are more readily checked for faulty welds by radiographic analysis. Further, due to the smooth transitions at the tank corners, excessive areas of stress concentration are avoided.

Now, with reference to FIGS. 8a and 8b, the corrugated top and sides of the tank, and the corrugated bottom of the tank will be described. The side and top corrugations are shown at 94 and the bottom corrugations are shown at 96. As can be seen, the depth of the corrugations in the top and sides of the tank is less than the depth of the corrugations in the bottom of the tank. This is the result of the relationship between the depth of the corrugation and the amount of stiffening provided by the corrugated wall. That is, the greater is the depth of the corrugation, the greater is the stiffening. Naturally, because the stress experienced by the bottom of the tank is substantially greater than the stress experienced by the sides and top of the tank, it is desirable that the bottom of the tank be structurally more sound than the remaining portions of the tank.

As can be seen in FIGS. 8a and 8b, the depth of the corrugations in the sides and top is 10 inches and the depth of the corrugations in the bottom is 111/2 inches. Naturally, these dimensions are given as examples only, and may be varied in accordance with the structural requirements of the particular tank. Further, while the sides and top could be corrugated to 111/2 inches, for uniformity, such design would be economically unsound.

The smallest distance between the tank corrugations, both in FIG. 8a and FIG. 8b, is approximately 10 inches. As noted previously, this dimension might be increased so as to provide for inspection access between all portions of the corrugated walls. For example, the narrowest dimension might be increased from approximately 10 inches to approximately 18 inches, the 18 inch dimension allowing passage of the man of average size.

As also seen in FIGS. 8a and 8b, the flats on the corrugations are longer in the corrugated bottom 96 than in the corrugated top and sides 94 of the tank. The increased depth of the corrugations in the bottom wall and the placement of the longitudinal girders make such increased dimension possible. Naturally, the specific dimensions of the corrugations depend upon the use of the tank and the anticipated stress expected to be encountered thereby.

Above, several embodiments of the present invention have been described. It should be appreciated, however, that these embodiments are described for purposes of illustration only and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is the intent that the invention not be limited by the above but be limited only as defined in the appended claims.

Claims

We claim:

1. A double wall cargo tank for the marine transportation of liquefied gases, such as methane and the like, at atmospheric pressure and at cryogenic temperature, the cargo tank comprising: an inner wall having corrugations defined therein, said inner wall defining a first liquid-tight enclosure; an outer wall having corrugations defined therein, spaced from and enclosing said inner wall, said outer wall defining a second liquid-tight enclosure; a wall space defined between said inner and said outer walls, said inner and said outer walls being arranged so that their undulations projecting into the wall space are aligned and in opposed relation perpendicularly of the planess of the walls and their undulations projecting out of the wall space are aligned and in opposed relation perpendicularly of the planess of the walls; a plurality of webs rigidly connected to said corrugated inner wall, extending into the tank defined by said inner wall a substantial portion of the transverse dimensions of the tank defined by said inner wall, said webs extending transversely of said inner wall corrugations and serving to support said inner wall; a plurality of diaphragms, each rigidly connected both to said inner and said outer walls, each having its plane positioned within said wall space, and each being aligned with the plane of a respective web, said diaphragms serving to support said outer wall; and means for stabilizing the portions of said webs extending into the tank defined by the inner wall including a plurality of struts, each of said struts extending perpendicularly and being rigidly connected to the innermost region of selected ones of said webs.

2. The cargo tank defined in claim 1, and further comprising a plurality of spaced longitudinal girders rigidly connected to the bottom of said cargo tank and serving to transmit foundation loads into the tank structures.

3. The cargo tank defined in claim 1, and further comprising entry means for gaining access to said wall space.

4. The cargo tank recited in claim 1, wherein the corrugations on the tank bottom are of a depth different than the corrugations in the tank top and sides.

5. The cargo tank defined in claim 1, wherein said cargo tank is mounted in the hold of a ship, and further comprising: support members for supporting the cargo tank only at the bottom thereof.

6. The cargo tank recited in claim 5, wherein said support members serve the dual function of supporting and keying said tank.

7. The cargo tank recited in claim 5, and further comprising anti-floating chocks for preventing the tank from rising in its hold if said hold should become flooded.

8. The cargo tank recited in claim 1, wherein the corrugations in the tank side walls are horizontally oriented.

9. The cargo tank recited in claim 8, wherein said webs and said diaphragms are vertically oriented.

10. The cargo tank recited in claim 1, and further comprising: a longitudinal bulkhead dividing the cargo tank into two sections of equal volume; and a transverse swash bulkhead dividing the cargo tank into two sections of approximately equal volume; said longitudinal and transverse bulkheads, together, dividing the cargo tank into four compartments of equal volume.

11. The cargo tank recited in claim 10, wherein said bulkheads are corrugated.

12. The cargo tank recited in claim 10, wherein both the longitudinal and the transverse bulkheads are provided with a plurality of openings therein, these openings providing communication between each of said four compartments of equal volume.

13. The cargo tank recited in claim 12, wherein the minimum spacing between the inner and the outer walls of said cargo tank permits the passage of a workman for purposes of inspection.

14. The cargo tank recited in claim 1, wherein the transitions between the top, sides and bottom of said tank are smooth transitions.

15. The cargo tank defined in claim 14, wherein the corrugations in the top of the tank are oriented in the same direction as are the corrugations in the bottom of the tank.

16. The cargo tank defined in claim 14, wherein all welds in both the inner and the outer walls are either seam welds or butt welds.

17. The cargo tank recited in claim 14, wherein certain of the transitions between the tank sides and the tank top and bottom comprise: a pair of smoothly curved plates associated, respectively, with said inner and said outer walls and adapted to rigidly connect the tank sides to the associated tank top or tank bottom; a pair of taper regions associated, respectively, with said inner and said outer walls in the tank top or the tank bottom wherein the corrugated inner and outer walls are tapered into flat plates, the spacing between the flat plates in said taper regions being equal to the maximum spacing between the corrugated inner and outer walls; said smoothly curved plates each being connected, at one side, to a respective flat plate in a taper region, and, at the other side, to the associated tank sides at an area of maximum spacing between the corrugated inner and outer walls.

18. The cargo tank recited in claim 14, wherein certain of the transitions between the tank sides and the tank top and bottom comprise: a pair of smoothly curved plates associated, respectively, with said inner and said outer walls and adapted to rigidly connect the tank sides to the associated tank top or tank bottom; a first pair of taper regions associated, respectively, with said inner and said outer walls in the tank top or the tank bottom wherein the corrugated inner and outer walls are tapered into flat plates, the spacing between the flat plates in said taper regions being equal to the maximum spacing between the corrugated inner and outer walls; a second pair of taper regions associated, respectively, with said inner and said outer walls in the tank sides wherein the corrugated inner and outer walls are tapered into flat plates, the spacing between the flat plates in said taper regions being equal to the maximum spacing between the corrugated inner and outer walls; said smoothly curved plates each being connected, at one side, to a respective flat plate in said first pair of taper regions, and, at the other side, to a respective flat plate in said second pair of taper regions.

19. The cargo tank recited in claim 14, wherein certain of the transitions between the tank sides and the tank top and bottom comprise: a pair of smoothly curved plates associated, respectively, with said inner and said outer walls and adapted to rigidly connect the tank sides to the associated tank top or tank bottom; said smoothly curved plates each being connected, at one side, to a wall of the associated tank side at an area of maximum spacing between the corrugated inner and outer walls, and, at the other side, to a wall of the associated tank top or bottom at an area of maximum spacing between the corrugated inner and outer walls.

20. The cargo tank defined in claim 14 wherein certain of the transitions between the tank sides and between the tank sides and the tank top and bottom comprise:

corrugation transition pieces each rigidly connected, respectively, to an inner and an outer side wall of the tank; cylindrical

cylindrical vertical corner pieces of arcuate transverse cross section rigidly connected between respective pairs of said transition pieces that are rigidly connected to adjacent sides of the tank;

cylindrical horizontal corner pieces of arcuate transverse cross section, each connected, respectively, between an inner and an outer wall of the tank sides and an inner and an outer wall of the tank top and bottom; and

additional corner pieces connected between respective ones of said vertical corner pieces and said horizontal corner pieces.

21. The cargo tank as in claim 20 wherein said additional corner pieces each define a smooth surface defining one-eighth of a sphere.

22. The cargo tank as in claim 20 wherein said corrugation transition pieces each define along its length a series of transverse channel-shaped members of varying depth defined by a first trapezoidal-shaped surface, first and second triangular-shaped surfaces connected to said first trapizoidal-shaped surface, and first and second rectangular-shaped surfaces connected, respectively, to said first and second triangular-shaped surfaces.

23. The cargo tank as in claim 22 wherein said triangular-shaped surfaces and said rectangular-shaped surfaces are coplanar with predetermined portions of said tank sides.