US3759209A

US3759209A - Grid system for external insulation tanker

Info

Publication number: US3759209A
Application number: US00144422A
Authority: US
Inventors: F Iarossi; W Cowles
Original assignee: Exxon Corp
Current assignee: Exxon Mobil Corp
Priority date: 1971-05-18
Filing date: 1971-05-18
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18

Abstract

A tanker vessel intended especially for the transport of liquid cargoes at temperatures differing from ambient temperature having external insulation covering the midbody of the vessel. The insulation is secured to the vessel midbody by means of a grid of intersecting frames or firring members attached to the vessel hull with the insulating material being fitted, foamed or sprayed in the lattice spaces defined by the intersecting members. An outer covering or skin may be disposed over the insulation to provide a watertight and abrasion resistant skin that will prevent damage to or deterioration of the external insulation.

Description

0 United States Patent 1 [In 3,759,209

Iarossi et a1. Sept. 18, 1973 GRID SYSTEM FOR EXTERNAL 416,428 12/1889 Sinclair 52/348 x INSULATION TANKER itozlnerui...i 1;

, 01' on e a [75] Inventors: Frank J. larossi, Middletown, N.J.;

Walter Cowles Colman Surrey Primary Examiner-Milton Buchler England Assistant Examiner-S. D. Basinger [73] Assignees Esso Research and Engineering Attorney-F. Donald Paris et al.

Company, Linden, NJ.

[22] Filed: May 18, 1971 [57] ABSTRACT [21] Appl. No.: 144,422 A tanker vessel intended especially for the transport of liquid cargoes at temperatures differing from ambient tern erature havin external insulation coverin the 52 US. P g g Int g s hi mldbody of the vessel. The insulation 18 secured to the [58] Field of Search i i i/ 72, 73, 74 R, pl by "f 0f "f fi fi 14/74 A, 219, 220; 220,9 LG, 9 R 9 A 14, rames or irrmg mem ers attac e to t e vesse u 1552848 667 668 with the insulating material being fitted, foamed or sprayed in the lattice spaces defined by the intersecting [561 ZZZ?ilfiti'laiiifiififfillfif325225253823$32523 UNITED STATES PATENTS resistant skin that will prevent damage to or deterio- 3,283,734 11/1966 Gonnan 114/74 A ration of the external insulation. 3,339,778 9/1967 Herrenschmidt 220/9 LG 2,288,104 6/1942 Pasquier 52/668 X 12 Claims, 9 Drawing Figures 22 3: fl "1 1 Q H1 4 411* F 5 l e g a 24 7? l l l li 41* i- 5 t a GRID SYSTEM FOR EXTERNAL INSULATION TANKER BACKGROUND OF THE INVENTION The present invention relates to cryogenic liquidcarrying tankers and, more particularly, to an externally insulated LNG tanker wherein the tanker may comprise a single or double shell internally stiffened both longitudinally and transversely and cargo sections subdivided into tank spaces by longitudinal and transverse bulkheads within the tanker shell forming the outer tank boundary.

It is well known that the waterborne transportation of liquefied natural gas at or near atmospheric pressure has required radical departures from conventional tanker design. Since at cryogenic temperature the steel normally employed in ship construction is so brittle that it no longer provides structural integrity, the major design effort has been directed toward the development of satisfactory tank systems to contain the cryogenie cargo apart from the ships structure.

To cop with the problem of low temperature embrittlement of mild steel, a variety of designs have been provided for independent or self-supporting integrated or membrane tanks. These prior art solutions have proven to be relatively unsatisfactory in that not only do they provide an LNG ship which is significantly more expensive than conventional tanker designs of similar capacity, but the ship is dependent upon the integrity of a multitude of barrier and warning systems for structural security and in the case of membrane tanks the question of long term durability is raised.

The novel construction and arrangement of the present invention for a grid system for securing the external insulation to the hull of a tanker preferably is employed in conjunction with the utilization of low temperature nickel alloy steel or a like material for the hull structure throughout the cargo section or midbody of the vessel. Since at cryogenic temperatures nickel steel possesses mechanical properties superior to those or ordinary structural steel, many of the problems which have greatly complicated previous LNG ships are bypassed. Thus, a 9 percent nickel steel hull or the like would be resistant to a brittle fracture at temperature as low as 320F. and would provide a suitable container for the liquefied natural gas cargo. One such typical vessel construction employing an externally insulated nickel steel hull is disclosed in the U. S. Pat. No. 3,283,734, assigned to the assignee to which the present application will be assigned. This foregoing Gorman patent merely discloses the broad concept of employing external insulation in connection with a nickel steel hull, but does not disclose or suggest specific details for securement of the insulation to the hull of the vessel.

The present invention contemplates utilizing a grid of intersecting frames or firring members attached to the hull in a suitable manner to be described in detail hereinafter. The external insulation material can be fitted, foamed or sprayed within the lattice spaces formed by the grid. These firring members may, for example, be formed from balsa wood, hard rubber, composition board, high density polyurethane, or some other simi- Iarly suitable materials which combine satisfactory encompass the entire deck, bottom and/or side shell of the vessel, but may encompass a localized area only. Such a localized grid system could be attached to the hull so as to transfer impact loads such as may result from docking or berthing through the insulation to the ships hull. The remainder of the ship which is not provided with such a grid system may utilize an alternate type of thermal insulation system which may comprise a low density, organic foam type material such as rigid polyurethane foam insulation that could be sprayed on the exterior of the hull in place of the firring in those areas where loading would not be excessive and would provide both the insulation and load bearing functions. In either case there would be provided an outer protective covering or skin that has suitable qualities of strength, toughness and permeability. This outer covering would be secured suitably over the insulation to provide a watertight and abrasion resistant skin for preventing damage to or deterioration of the external insulation.

In addition to those advantages described above in connection with the present invention, various other advantages will be evident from an understanding of this disclosure. The present invention comprises the combinations and arrangements as disclosed and illustrated in the presently preferred embodiment of the invention, which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction and advantages of it when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view of an externally insulated tanker incorporating the present invention;

FIG. 2 is an enlarged cross-sectional view taken substantially on the line 22 of FIG. 1 illustrating details of the center tank, wing tank and external insulation;

FIG. 3 is an enlarged cross-sectional view taken substantially on the line 33 of FIG. 2 illustrating the details of the novel grid system constructed in accordance with the teachings of the present invention;

FIG. 4 is a cross-sectional view taken substantially on the line 44 of FIG. 3 illustrating the preferred arrangement of the grid firring relative to the vessel hull.

FIG. 5 is an enlarged cross-sectional view taken substantially on the line 5--5 of FIG. 3 illustrating structural details of the firring construction;

FIG. 6 is an enlarged cross-sectional view taken substantially on the line 66 of FIG. 3 illustrating further structural details of the firring;

FIG. 7 is an exploded perspective view of a portion of the grid system of FIG. 3;

FIG. 8 is an alternate construction to that shown in FIGS. 3 through 6 for securing the firing members to the vessel hull; and

FIG. 9 is a second alternate construction to that shown in FIGS. 3 and 6 for securing the firring members to the vessel hull.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Having reference to the drawings, the present invention as illustrated in FIG. 1 is embodied in an externally insulated tanker having a nickel steel plate hull at least at its midbody, reference being made to the U. S. Pat No. 3,283,734 for a more complete and detailed explanation of the broad concept. Also, reference may be had to U.S. Pat. No. 3,671,315, and Ser. No. 118,445 (RM-61 l filed on Feb. 24, 1971 entitled CENTRAL- IZED CARGO HANDLING SYSTEM FOR CRYO- GENIC VESSELS, both of which relate to different construction details of an externally insulated tanker and both of which are to be assigned to the same assignee as that of the present application and the Gorman patent.

The tanker generally comprises a hull H which comprises a forward hull portion or bow 10, an after hull portion or stern 11, both of which are fabricated conventionally from mild steel plate or mild steel strengthening members and both of which may typically include suitable ballast areas 129, and a cargo-carrying section or midbody 13. Location between each of the ballast areas 12 and the cargo-carrying midbody 13 there may be provided a temperature transition area 14, specific details of which are disclosed and claimed in the aforementioned copending US. Pat. No. 3,671,315.

In accordance with the teachings of the aforementioned Gorman patent, the midbody 13 may be fabricated from a metal plate (e.g., substantially 9 percent nickel steel) possessing physical and mechanical properties compatible with the particular cargo to be carried. The midbody 13 may be subdivided into a plurality of individual center cargo holds 15 and wring tanks 16 disposed on either side of the centrally disposed tanks 15 formed by means of transverse bulkheads l7 and a single or plurality of longitudinal bulkheads 18 as shown. In accordance with a preferred embodiment of the present invention, although not in a limiting sense, the cargo midbody 13 is completely enveloped or clad externally with a suitable thermal insulation 19. Although the ships midbody structure has been disclosed as comprising material such as 9 percent nickel steel for cryogenic products such as methane and the like, in the case of other low temperature products such as LPG, usual tank quality steel would be sufficient, while ordinary quality steel would suffice for higher temperature products.

The present invention, is directed towards a system for securing the externally insulation 19 in place on the ship's hull. As illustrated schematically in FIG. 2, the insulation 19 is provided with a suitable outer covering 20. This covering or skin is designed to have suitable qualities of strength, toughness and permeability. It is possible for the covering to be laminated, laid over or sprayed on the insulation 19 to provide a watertight, abrasion-resistant skin that will prevent any damage to or deterioration of the external insulation. The underwater portion of the skin 20 may incorporate satisfactory anti-fouling properties or may be suitably coated. Those portions of the skin which may be exposed to sources of ignition would necessarily incorporate a satisfactory fire retardant chemical to provide it with the necessary fire retarding properties. The outer covering may be constructed of a reinforced rubber compound such as butyl or neoprene installed in circumferential or longitudinal strips of perhaps two meters width. If the covering is applied in multiple thicknesses, the first thickness may be secured mechanically to the firring members, while the second thickness can be bonded to the first or under covering. All joints are made sufficiently tight by means of a suitable adhesive. To insure water tightness the joints may be staggered. Also, the

multiple layers each may possess different properties as may be required by the particular system. Alterna-,

tively, a single thickness may be employed with the joints being vulcanized in place. Alternate covering to the foregoing may comprise a coating of reinforced plastic, latex resin, vinyl, polyurethane or other suitable material which could be sprayed over the hull insulation and the grid system. This coating may be reinforced with the glass cloth, nylon, polyester or some other suitable material to provide the necessary strength. Since the tanker will contract upon cool down, this will place the insulation system in compression and will in turn tend to buckle the protective cover 20 secured thereto. To avoid this tendency which may create ripples in the skin surface, the protective cover can be tensioned during installation to offset the compression expected during cool down. This will result in a tighter protective cover and a hull with a lower resistance.

Turning now to FIG. 3, there is shown the novel grid system for securing the insulation 19 in place. Basically the grid system comprises a plurality of intersecting horizontal and vertically disposed

lirring members

21 and 22. The

flrring members

21, 22 are arranged and secured to the hull in a novel manner to be described in detail hereinafter to define a plurality of uniform lattice spaces 23. The insulation 19 may comprise a rigid foam which either can be fitted, foam or sprayed into these spaces 23. The firring members 21. and 22 may comprise balsa wood, hard rubber, composition board, or other similar materials which combine satisfactory strength, rigidity and thermal insulating properties. These firring members may be provided in two or more thicknesses and also may comprise incremental lengths. The connecting joints between adjacent ones of the firring members are disposed such that the joint of adjoining vertical members does not coincide, but is staggered relative to the joint for adjoining horizontal members. According to one preferred embodiment of the present invention, the horizontal firring members 21 are secured to the hull by means or vertically spaced 9 percent nickel flat bars 24 which extend longitudinally of the hull in the area containing the grid and protrude perpendicular outward therefrom. As best shown in FIG. 4, the flat bar 24 is provided with longitudinal spaced openings 25, each of which are designed to receive a 9 nickel or stainless steel through bolt 26. The bolt extends through the horizontal firring members 21 at predetermined locations and at the point where each of the bolts 26 are located, the upper and lower surfaces of the horizontal tirring members are provided with vertically aligned countersunk or routed recesses 27 such that the through bolt extends into the recesses for receiving a nut 28 at each end to securely hold the horizontal firring member to the ships hull. To accomodate the flat bar 24, each of the horizontal firring members 21 is provided with a centrally located rear channel or opening 29 which extends for the length thereof. To provide a seal between the adjacent surface of the horizontal firring members (as well as the vertical firring members) and the hull where they are contiguous, there is provided a suitable bedding compound, such as latex cement, designated 30. Although not shown, appropriate spaces may be left between adjacent lengths of the firring members, both vertical and horizontal, to accommodate contraction and expansion of the ships hull. A suitable compressible materal such as PVC foam mat be provided between these members to take up and relative movement.

The horizontal firring members is similarly constructed and each is provided with an intermediate twosides apertured recess 31 which are designed to received the vertical members therein at the point where the vertical member lengths are joined together. The depth of the recess 31 is such that the outer surface of the vertical members will be flush with that of the horizontal members. As best shown in FIG. 7, one end of the horizontal firring member is routed to form an outer L-shaped recess or notch 32, having a split in flange 33, while the opposite end is formed both on its outer and inner sides with opposing similar L-shaped notches 34 with a central apertured flange 35 disposed therebetween. The inner one of the notches 34 is designed to accommodate or is complemental to the apertured flange 35 of an adjoining horizontal member. As shown in FIG. 5, the vertical firring members 22 also provided with intermediate recesses 36 which are similar to the recess 31 formed in the horizontal member. To secure the vertical members to the horizontal members, which latter members are secured to the ships hull as shown in FIG. 4, a bolt 37 is passed through the aligned openings of 33, 35 and 36 and nuts are threaded at either end thereof to secure the bolt in place and thus, the vertical member to the hull through the horizontal member. At the location where the adjacent lengths of vertical members are joined together there is provided a laptype joint 38 as shown in FIG. 6. Each vertical firring member 22 is formed at one end with a pair of vertically offset opposed L-shaped

recesses

39 and 40 with an apertured flange 41 disposed therebetween. The recess or notch 39 is located furthest away from the hull and is smaller in size than inner recess 40. At the other end of each vertical member there is formed a routed step-like configuration comprising an apertured outer flange or ledge 42, a central abutment member 43 which together with the inner surface of flange 42 defines an outer notch 44 and an inner notch 45 offset vertically relative to notch 44. The latter step-like end configuration is designed to be complimentary to the opposite end configuration of the vertical member as shown in FIG. 7. Each lap joint between vertical members as designed to be received in a corresponding recess 31 of the horizontal members. Thus, as shown in FIG. 6, at this particular point in the grid system the horizontal members are secured to the ships hull as described previously in connection with FIG. 4. The

apertured flanges

41 and 42 of the adjacent vertical members are aligned with the recess 31 to receive a bolt 46 that extends into the channel 29 of the horizontal member at one end and at the other end protrudes into the opening in the outer flange 42. As with regard to the other connections, nuts are provided at either end of the bolt to secure the members together.

It is within the scope of this invention to provide firring members of two or more thicknesses and two or more incremental lengths. These members, as disclosed heretofore, may be secured to the shell by means of studs and countersunk nuts. In the case of employing studs as disclosed in connection with FIGS. 1 through 7, all but a single one of the stud holes may be slotted to permit contraction and expansion of the shell relative to the firring members. These studs may be welded either directly to the hull (see FIGS. 8 and 9) or, as i1- lustrated and described in connection with the preferred embodiment, bolted through steel flate bars which are in turn welded to the hull. Should the framing comprise two or more thicknesses, the outer layers may be fastened by means of lag screws or bonded with a suitable adhesive. Any butt joints between adjacent firring members preferably should be staggered as disclosed and shown to block any convective currents. Also, it should be recognized that the insulation which is fitted in the lattice spaces may be in two or more thicknesses matching the thickness of the firring. The outer firring member may be narrower than the inner firring member so as to provide an effective overlap of insulation. Although the grid system, according to the preferred embodiment, is shown as covering the entire cargo midbody, this need not necessarily be the case. Thus, the system may be provided in those localized areas only where it is necessary to transfer impact loads through the insulation to the ships hull. The other areas of the ships hull may be provided with an alternate insulation system such as discussed in the beginning of the specification. The particuar type of outer covering already has been discussed and, thus, will not be gone into in further detail.

It will be appreciated from the foregoing description that a novel construction and arrangement for a grid system for securing external insulation to a ship has been provided. It should be understood that while there is illustrated and described herein a specific preferred construction and arrangement, the present disclosure is intended to be representative of a preferred embodiment only and that a various changes may be made herein without departure from the clear teachings of the present disclosure. For example, the grid system may be installed at an angle to increase the heat loss path so as to minimize heat loss through the grid on an externally insulated tanker. Thus, by disposing the firring members at an angle relative to the hull by means ofa shoe or the like secured to the hull for positioning the grid members, the foregoing may be accomplished. Also, the outer protective covering can be fastened mechanically to the grid system by various means, one of which comprises the use of a clamping bar being received in a flat head fastener secured to the grid members. The covering is held in place by disposing it between the clamping bar and the grid. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.

Having thus set forth the nature of the invention, what is claimed is:

1. An externally insulated tanker for the transportation of liquid cargoes at nonambient temperatures, comprising, in combination:

a. a hull having forward and after portions interconnected by b. a midbody portion adapted for containing the liquid cargo therein;

c. thermal insulation secured to the exterior of said hull;

d. grid means for securing said thermal insulation to said midbody, said grid means comprising a plurality of intersecting firring members arranged and constructed to form a substantially flush outer surface and define a plurality of lattice spaces therebetween for receiving and holding in place said thermal insulation relative to said hull, each of said firring members having thermal insulating capability; and

e. means for operably securing said firring members to said hull.

2. An externally insulated tanker according to claim 1 wherein an outer covering is disposed over said thermal insulation to provide a substantially watertight and abrasion resistant skin that will prevent damage to or deterioration of said thermal insulation.

3. An externally insulated tanker according to claim 1 wherein said grid system means encompasses the entire midbody of said tanker.

4. An externally insulated tanker according to claim 1 wherein said grid means encompasses those localized areas only of said hull which receive the load impacts that may result from docking or berthing of the tanker.

5. An externally insulated tanker according to claim 1 wherein said grid means comprises a plurality of horizontal and vertical intersecting firring members.

6. An externally insulated tanker according to claim 5 wherein said firring members include a notched configuration at each end thereof and a recess disposed intermediate of said ends.

7. An externally insulated tanker according to claim 5 wherein each of said horizontal firring members is provided at opposing ends thereof with first and second substantially complementary notched configurations and each of said vertical firring members is provided at opposing ends thereof with third and fourth substantially complementary notched configurations, and each of said vertical and horizontal firring members also being provided with a recess disposed intermediate of said ends; said first notched configuration being arranged and constructed to receive said second notched configuration of an adjoining one of said horizontal firring members on one side thereof, and said third notched configuration being constructed and arranged to receive said fourth notched configuration of an adjoining one of said vertical firring members, whereby said horizontal and vertical firring members form a substantially flush surface.

8. An externally insulated tanker according to claim 5 wherein each of said horizontal firring members is of designed to receive a corresponding one of a plurality of vertically spaced horizontal flat bars welded along their length to said hull, and means for securing said flat bars to said horizontal firring members.

9. An externally insulated tanker according to claim 5 wherein the connecting joints between are disposed in generally opposing directions to prevent convective currents.

10. An externally insulated tanker according to claim 1 wherein a plurality of vertically spaced longitudinally extending flat bars are secured along their lengths to said hull, and predetermined ones of said firring members include longitudinal grooves for receiving and being operably secured to said bars.

11. An externally insulated tanker according to claim 1 wherein said firring members are of different lengths.

12. An externally insulated tanker according to claim 1 wherein said firring members are constructed and arranged to accommodate contraction and expansion of said tanker hull.

t i h t

Claims

1. An externally insulated tanker for the transportation of liquid cargoes at nonambient temperatures, comprising, in combination: a. a hull having forward and after portions interconnected by b. a midbody portion adapted for containing the liquid cargo therein; c. thermal insulation secured to the exterior of said hull; d. grid means for securing said thermal insulation to said midbody, said grid means comprising a plurality of intersecting firring members arranged and constructed to form a substantially flush outer surface and define a plurality of lattice spaces therebetween for receiving and holding in place said thermal insulation relative to said hull, each of said firring members having thermal insulating capability; and e. means for operably securing said firring members to said hull.

8. An externally insulated tanker according to claim 5 wherein each of said horizontal firring members is provided with a rearwardly open channel extending the length thereof designed to receive a corresponding one of a plurality of vertically spaced horizontal flat bars welded along their length to said hull, and means for securing said flat bars to said horizontal firring members.

9. An externally insulated tanker according to claim 5 wherein the connecting joints between adjacent ones of said horizontal members and said vertical members are disposed in generally opposing directions to prevent convective currents.