U.S. patent number 3,583,351 [Application Number 04/770,992] was granted by the patent office on 1971-06-08 for vessel for transporting liquefied hydrocarbon.
This patent grant is currently assigned to Esso Research and Engineering Company. Invention is credited to Paul T. Gorman.
United States Patent |
3,583,351 |
Gorman |
June 8, 1971 |
VESSEL FOR TRANSPORTING LIQUEFIED HYDROCARBON
Abstract
A ship for transporting liquids at very low temperatures at
about atmospheric pressure, comprising an inner and outer ordinary
shipbuilding steel hull and single walled, self-supporting, low
temperature material tanks covered with an insulation system which
serves to prevent cold from reaching the ordinary shipbuilding
steel. The inner walls of the inner steel hull are also insulated
as further protection against any leaks which might develop in the
primary tanks. The tanks are supported on insulation-bearing blocks
and restrained by vertical keys located at the center of the tank
sides and ends.
Inventors: |
Gorman; Paul T. (Arenzano,
Genoa, IT) |
Assignee: |
Esso Research and Engineering
Company (N/A)
|
Family
ID: |
25090358 |
Appl.
No.: |
04/770,992 |
Filed: |
October 28, 1968 |
Current U.S.
Class: |
114/74A; 220/902;
220/560.15; 220/560.07; 220/901 |
Current CPC
Class: |
B63B
25/16 (20130101); F17C 3/025 (20130101); F17C
2260/033 (20130101); Y10S 220/902 (20130101); F17C
2223/0161 (20130101); F17C 2205/0119 (20130101); F17C
2203/0648 (20130101); F17C 2203/0629 (20130101); F17C
2221/033 (20130101); Y10S 220/901 (20130101); F17C
2223/033 (20130101); F17C 2270/0105 (20130101); F17C
2203/0333 (20130101); F17C 2203/0337 (20130101); F17C
2260/011 (20130101); F17C 2203/0646 (20130101); F17C
2205/018 (20130101); F17C 2270/0134 (20130101); F17C
2205/0192 (20130101); F17C 2203/0631 (20130101); F17C
2209/227 (20130101); F17C 2209/232 (20130101); F17C
2201/0157 (20130101); F17C 2203/0607 (20130101); F17C
2260/013 (20130101); F17C 2203/0639 (20130101); F17C
2260/015 (20130101); F17C 2209/228 (20130101); F17C
2203/035 (20130101); F17C 2209/221 (20130101) |
Current International
Class: |
F17C
3/02 (20060101); F17C 3/00 (20060101); B63B
25/16 (20060101); B63B 25/00 (20060101); B63b
025/08 () |
Field of
Search: |
;114/74,74A
;220/15,9A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Blix; Trygve M.
Claims
What I claim is:
1. In a tanker for carrying liquefied gases maintained at
atmospheric pressure and cryogenic temperatures, said tanker having
an inner hull and an outer hull and a cargo hold partially defined
by said inner hull, the improved system which comprises:
a. a self-supporting cargo tank supported within said cargo
hold;
b. a first multilayer insulation system positioned on the exterior
of said cargo tank; and
c. a secondary barrier independent of said first multilayer
insulation system and comprising a plurality of individual
insulation panels affixed on the interior walls of said inner hull
and disposed in spaced relation relative to said first multilayer
insulation system.
2. The system of claim 1 wherein said multilayer insulation system
comprises, a first course of insulation panels, an intermediate
thermally nonconductive support wall affixed to the exterior walls
of said cargo tank for holding said first course of panels against
the exterior of said cargo tank, and a second insulation course
comprising a plurality of individual insulating panels affixed to
said intermediate support wall.
3. The system of claim 2 wherein said intermediate support wall
comprises a plurality of panels which are affixed to said exterior
walls of said cargo tank in a manner which allows slippage between
said intermediate support wall panels and said first course of
insulation panels.
4. The system of claim 1 wherein the individual panels comprising
said secondary barrier comprise fiberglass reinforced plastic
shells filled with a foamed plastic insulation material.
5. An improved insulation system for a cryogenic cargo tanker
having an inner and outer hull of the type wherein a primary
self-supporting cargo tank is positioned within said inner hull,
said system comprising, a multilayer insulation panel system
affixed to the exterior of said self-supporting cargo tank, and a
secondary barrier independent of said multilayer insulation panel
system comprising a plurality of insulation panels arrayed in
end-to-end and side-by-side configuration on the interior of said
inner hull so as to define a liquid and vaportight barrier and
being disposed in spaced relation relative to said multilayer
insulation panel system, said secondary barrier being normally
protected from the extremes of cryogenic temperatures by the
insulating effect of said multilayer insulation panel system
affixed to the exterior of said cargo tanks.
6. The system of claim 5 wherein said multilayer insulation panel
system comprises a first course of insulation panels, and an
intermediate thermally nonconductive support wall comprising a
plurality of individual panels, which wall is fastened to said
cargo tank so as to hold said first course of insulation panels
against the exterior of said cargo tank whereby slippage is allowed
between said intermediate support wall panels and said first course
of insulation panels
7. A tanker for carrying cryogenic cargoes which comprises, an
outer hull, a hold defining inner hull positioned within said outer
hull, a liquefied gas self-supporting cargo tank positioned within
said hold, first insulating means disposed on the exterior walls of
said self-supporting cargo tank, and second insulating means
independent of said first insulating means disposed on the interior
walls of said hold and disposed in spaced relation relative to said
first insulating means, said second insulating means serving as a
secondary barrier and being normally protected from the extremes of
cryogenic temperatures by the insulating effect of said first
insulating means.
8. A tanker according to claim 7 including means for securing said
first insulating means to the exterior walls of said
self-supporting cargo tank such that such first insulating means is
allowed to contract independent of said self-supporting cargo tank,
thereby to minimize thermal stresses in said first insulating
means.
9. A tanker according to claim 7 wherein said second insulating
means comprises a plurality of panels, and including means for
joining said panels so as to form a liquid and vapor barrier
whereby in the event of a failure in said Self-supporting tank,
said second insulating means serves as a container for the
cargo.
10. A tanker according to claim 7 wherein the outermost surface of
said first insulating means and the innermost surface of said
second insulating means are disposed on said exterior walls and
said interior walls, respectively, in spaced relation thereby to
define an access space therebetween.
11. A tanker for carrying cryogenic cargoes comprising at least one
hull which effectively defines a cargo hold, a self-supporting
cargo tank positioned within said cargo hold, first insulating
means disposed on the exterior walls of said self-supporting cargo
tank, and second insulating means separate from said first
insulating means disposed on the interior walls of said hold in
spaced relation relative to said first insulating means so as to
define an access space between said first insulating means and said
second insulating means, said second insulating means serving as a
secondary barrier and normally being protected from the extremes of
cryogenic temperatures by the insulating effect of said first
insulating means, whereby said second insulating means serves as a
container for the cargo in the event of failure of said
self-supporting cargo tank.
Description
BACKGROUND OF THE INVENTION
This invention relates to the storing and shipping of liquefied
hydrocarbons and more particularly, comprises improvements in the
construction of those maritime vessels which transport liquefied
hydrocarbons at very low temperatures.
It is well known that hydrocarbons which are in a gaseous state in
normal conditions of temperature and pressure may be reduced to a
liquefied state by high pressure or low temperature, or a
combination of both. Regardless of which system is used to store
and transport liquefied hydrocarbons, there are a number of
difficult problems that are presented. For instance, the tanks used
to store the liquefied hydrocarbons under pressure must be strong
enough to resist the high pressure needed to liquefy the gas. The
weight involved in such tanks is very often objectionable because
it comprises a substantial portion of the total weight of the
vessel.
If low temperature is to be the medium for transporting the
hydrocarbon in a liquefied state, then problems of a different sort
are encountered. In the case of methane, a temperature of about
-260.degree. C. is required to achieve and maintain liquefaction at
atmospheric pressure. At such temperatures, ordinary steel becomes
brittle, generally losing its mechanical qualities and rendering it
incapable of withstanding the stress and strain to which the
structural portions of the vessel are normally subject. The
smallest leak can create contact between the transported product
and the shell plating of the tanker which is built of ordinary
steel, and this, of course, can possibly result in damage and even
total loss of the vessel.
Container systems for typical liquified gases must be of sufficient
strength and structural integrity to prevent the escape of the gas
therefrom since the supercooling effects of the liquefied gas would
be extremely deleterious to the ship's structure, which could
become embrittled and thereby result in overstressing of the
surrounding mild steel ship plate. Accordingly, in order to
maintain a high degree of safety, it has been well accepted and
statutorily required practice to include at least two liquid and
vapor type barriers in cryogenic containers employed in shipboard
applications for the isolation of the supercooled cargo from the
ship's structure.
Thus, it is the general object of this invention to improve the
storing and transporting of liquefied hydrocarbons at low
temperatures.
Another object of this invention is to provide a maritime vessel
for transporting liquefied hydrocarbons, the vessel having low
temperature storage tanks generally following the contours of the
vessel and supported in such a fashion as to allow for expansion
and contraction of the tanks, as well as flexing of the ship's
bulkheads and structural members.
Still another object is to provide a ship for transporting
liquefied hydrocarbons which meets safety and reliability
requirements in that it has two liquidtight barriers to provide a
substantially fail-safe system.
SUMMARY OF THE INVENTION
In accordance with the principle of the present invention, an
improved insulation system is provided for use with as
self-supporting cryogenic tank of the type fabricated from such a
low temperature resistant material such as aluminum alloys or 9
percent nickel steel. In a preferred embodiment of the invention,
an insulation system is provided which comprises, in part, a first
course of insulation which is secured to the exterior surfaces of
the self-supporting tank in such a manner as to allow it to
contract independently of the cargo tank, thereby minimizing
thermal stresses on this first course. A second insulation layer is
provided on the interior of an inner hull comprising part of the
ship's structure, which second layer is comprised of foam plastic
panels encapsulated in fiberglass reinforced plastic. These panels
are joined in a manner so that the entire second insulation layer
is liquid and vaportight and serves as a container of the cold
cargo in the event that a failure occurs in the self-supporting
tank.
A significant aspect of this invention is the relatively high
temperature of the plastic encapsulated insulation layer during
normal service conditions, which reduces the effects of continued
exposure to very low temperatures and thermal stress cycling on its
integrity.
For a more complete understanding of the present invention and its
advantages, reference should be made to the following detailed
description taken in conjunction with the accompanying drawings in
which:
FIG. 1 is a diagrammatic end view of the cryogenic cargo tank
itself.
FIG. 2 is a side elevational view of the tank shown in FIG. 1.
FIG. 3 is a plan view of the tank shown in FIG. 1.
FIG. 4 is a diagrammatic side elevation of the tank with
insulation, and also shows the key members on the tank.
FIG. 5 presents an end view of FIG. 4.
FIG. 6 is a bottom view of FIG. 4.
FIG. 7 is a diagrammatic sectional plan view showing the
installation of tank within the hull of a ship.
FIG. 8 is an enlarged sectional view taken along the line 8-8 of
FIG. 7.
FIG. 9 is a sectional view taken along the line 9-9 of FIG. 7.
FIG. 10 is a perspective view of the tank itself showing the metal
keys welded thereto.
FIG. 11 is a perspective view of the tank with its associated
insulation completely installed.
FIG. 12 is an enlarged sectional view of a portion of the
insulation course associated with the cargo tank.
FIG. 13 is a detail of the studs shown in FIG. 12.
FIG. 14 is a detail of the studs used at the corners of the
tank.
FIG. 15 is a side elevational view depicting the second step of the
fabrication and installation of the insulation on the tank.
FIG. 16 is a sectional view taken along the line 16-16 of FIG.
15.
FIG. 17 is a detail of the fastening nuts shown in FIG. 16.
FIG. 18 is a detail of the relationship of the holes shown in the
plywood sheets of FIG. 15.
FIG. 19 is a side elevational view depicting the third step in the
fabrication and installation of the insulation on the tank.
FIG. 20 is a sectional view taken along the line 20-20 of FIG.
19.
FIG. 21 is a detail of the stud screws shown in FIG. 20.
FIG. 22 shows a detail of the holes in the metal sheathing shown in
FIG. 19.
FIG. 23 is a perspective view (with parts broken away) showing
installation of the insulation on both inside and outside corners
and on one of the keys of the tank.
Referring to the figures in detail, FIGS. 1--3 show respectively an
end, side and top view of a cargo tank 37 which is to be utilized
in conjunction with the insulation system of the instant invention.
Tank 37 is of generally rectilinear prismatic shape and is provided
with a trunk section indicated at 38. The corners 43 of the main
portion of the tank, as well as those between the main portion of
the tank and its trunk section, are curved so as to avoid any
stress buildup in these areas.
FIGS. 4--6 respectively show a side view, end view and bottom view
of tank 37 covered with the first insulation course of the system
of the instant invention, indicated generally at 40 in FIG. 4. Tank
37 is also provided with keys (not shown in FIGS. 1--3) which will
be herein subsequently discussed. These keys are shown covered with
insulation 44 in FIGS. 4--6. Key bearing blocks 42, whose function
will also be further described, are installed in the keys.
Referring to FIG. 6, the primary cargo tank rests on bearing blocks
46 which may preferably be fabricated from balsa wood or the like,
and will also be discussed subsequently hereto.
FIG. 7 presents a diagrammatic sectional plan view showing the
installation of the insulated tank 40 within a ship's cargo hold,
indicated generally at 41. The ship is preferably of double hulled
construction, having an outer hull 48 and an inner hull 50.
Preferably, double walled transverse bulkheads 52 are disposed
between the sides of the inner hull 50. Each of the interior walls
defining hold 41 are provided with insulated brackets 54 which
define keyways to engage the keys 44 and their associated bearing
blocks 42 of tank 40. As may clearly be seen in FIG. 7, a second
insulation lining 51 is provided on the interior surface of inner
hull 50 and on surfaces of transverse bulkheads 52. As hereinbefore
indicated, insulation lining 51 is constructed so that it is liquid
and gastight and will serve as a container of the cold cargo in the
event that a failure occurs in the tank 37.
More specifically, layer 51 is comprised of a plurality of panels
which are generally similar to the fiberglass reinforced polyester
and polyurethane foam thermal insulating panels first disclosed in
U.S. Pat. No. 3,367,492 (Pratt et al.) for "Insulation System." In
general, as shown in FIG. 8, the continuous, effectively
dimensionally stable, secondary barrier 51 is established by
securing stepped insulation panels 14 through integral flanges 16
extending peripherally outwardly from the base portions thereof to
the inner hull plating 50 by means of a nut 15 and a Nelson stud
15'. Advantageously, the insulation panels 14 are approximately 5
feet .times. 25 feet in size, are generally symmetrical in shape,
and include glass fiber reinforced polyester shell 17 filled with
polyurethane foam 18. Each gap 19, formed between opposing faces 20
of adjacent insulating panels 14, is closed by a mating stepped
plug piece 21 constructed similarly to the insulating panels 14 of
a fiberglass reinforced polyester shell filled with polyurethane
foam and being correspondingly effectively dimensionally
stable.
The secondary barrier 51, defined by the end-to-end and
side-by-side array of panels and plug pieces, is made continuous
and liquidtight by the adherence of the plug pieces 21 to the
opposing step faces 20 of adjacent insulating panels by means of a
suitable adhesive sealer 22. As set forth in more detail in the
before-mentioned Pratt et al. application, the above described
insulating barrier 51 is effectively dimensionally stable and will
not undergo deleterious contraction when subjected to the extreme
temperatures (e.g. about -260.degree. F. for liquefied methane)
encountered in the cryogenic environments of liquefied hydrocarbon
transportation.
Referring now to FIG. 9, which is taken along the line 9-9 of FIG.
7, it may be seen that the means for supporting tank 40 within the
hold 41 includes a plurality of bearing blocks 46 which in turn are
supported by a plurality of supporting rails 60, which are affixed
to the bottom 56 of the hold 41. Supporting rails 60 may preferably
be made from a metal which retains its physical properties at
cryogenic temperatures, for example, 9 percent nickel steel.
FIG. 10 shows a perspective schematic view of tank 37 before the
first insulating course of the instant invention has been applied
thereto. As may be clearly seen, each of the keys 62 define a pair
of grooves 64 in their peripheral sides 65. Grooves 64 are adapted
to receive the bearing blocks 42 shown in FIG. 4. A diagrammatic
perspective view showing tank 37 as it would appear when covered
with the first insulating course of the instant invention is shown
in FIG. 11. Corners of the insulation are protected by a plurality
of metal sheathing angles indicated at 66. A plurality of batten
strips generally indicated at 67 are also shown. (The function of
these strips will be discussed in conjunction with FIGS.
19--22.)
Reference will now be had to FIGS. 12--23 in discussing a preferred
form of the first insulation course which is affixed to the
exterior of the primary cargo container 37. Referring first to FIG.
12, reference numeral 36 identifies the wall of the tank 37 to be
insulated. Affixed to wall 36 are a plurality of mounting means 72.
These mounting means are preferably aluminum studs having a base
portion 76 and a threaded portion 80. Studs 72 may be welded to
wall 36 as shown at 78 in FIG. 13. In a preferred embodiment these
studs have a nominal diameter of five-eighths inch and are disposed
on the wall 36 with a 2 feet .times. 2 feet nominal spacing. The
threaded portion 80 of studs 72 may be provided with a removable
impaling head 74, whose function will be discussed hereinafter. In
a preferred embodiment of the instant invention, the insulation
which is applied to the exterior of the tank 37 is preferable
constructed in two layers itself. The first layer or inner layer of
the primary tank insulation, which is indicated generally at 75 in
FIG. 12, is composed of a plurality of individual insulation panels
70. Panels 70 may be fabricated from any suitable insulation
material, but foam plastics of the type including polystyrene,
polyurethane and polyvinylchloride are particularly suitable. In
the preferred embodiment, polyvinylchloride is used to advantage.
The inner insulation panels of 70 are preferably 4 feet .times. 4
feet and about 2 inches thick. These panels are installed by being
impaled over the impaling heads 74. The first panel is properly
positioned and subsequent panels are then installed tightly against
the edges of the panel or panels that are already in place.
Impaling heads 74 are removed from the threaded portion of the
studs 72 as each panel is in place. It has been found that impaling
heads 74 may be constructed in the form of thin walled tubes with
sharpened end peripheries. Such a tube will core out a clean hole
in the insulation panel without spoiling the surface on
breakthrough and without necessitating the rotation of the cutting
tube during the piercing operation.
FIG. 14 illustrates the type of mounting means that are used to
install the insulation at the corners of the tank 37. Due to higher
stress conditions which invariably result at the intersections
between sides and bottoms, sides and tops, etc. of tanks, the studs
to be used at these locations should be stronger than the studs
used at other locations. In a preferred embodiment, additional
one-half achieved by utilizing an aluminum collar 82 which is
welded about its periphery to the tank 37 as indicated by reference
numeral 84 in FIG. 14.
Following the installation of foam panels 70, a structural support
layer indicated generally at 85 in FIG. 16 is installed. In the
preferred embodiment, this layer is comprised of a plurality of
individual plywood panels five-eights inch thick and 3 feet 111/2
inches square. As shown in FIG. 15, these panels are installed such
that a nominal gap of one-half inch exists between adjacent panels.
The plywood panels serve as structural members, and for this reason
each panel is to be located symmetrically with respect to the four
studs which support it. While the plywood panels primarily do not
serve as insulation, the space between panels nevertheless is
staggered with respect to the junctions between the blocks of inner
insulation to minimize heat leaks. The half-inch gap between the
panels are filled with compressed elastic foam gas skimming
material, indicated at 92 in FIG. 16, to further minimize heat
leaks.
FIG. 18 details the relationship of the predrilled holes which
exist in each of the plywood panels 86. Holes 96 [(a) and (c)] in
FIG. 18 are drilled such that there exists a clearance of .+-.1/8
inch with respect to the diameter of studs 72. Holes 98 indicated
at (b) and (d) in FIG. 18 are slotted. This configuration of holes
allows each panel to be symmetrically located with respect to the
four studs which support it. Each of the holes is surrounded by a
countersunk hole 90 which is adapted to receive the threaded nut 88
shown in detail in FIG. 17. Teflon washer 94 is interposed between
the enlarged head 97 of the nut 88 and that portion of the plywood
on which head 97 bears. The nuts 88 are tightened to a
predetermined level, and after this tighting operation the head of
stud 72 may be peened or spot welded so that nut 88 will not loosen
in service. As an important aspect of the instant invention, it is
to be noted that the nuts 88 are not tightened to the extent that
all spillage between the faces of the insulation panels 70 and the
plywood panels 86 would be eliminated. In this regard it may be
seen that the holes 96 and the slots 98 of the plywood panels and
their associated countersunk holes 90 allow limited displacement of
the plywood panels with respect to the studs and, hence, with
respect to the individual insulating panels 70. This allows the
structural layer composed of the individual plywood panels when
subjected to thermal contraction to be free floating within certain
defined limits.
The third major step in the fabrication of the insulation system to
be applied to the tank 37 is detailed in FIGS. 19--22. Referring to
FIG. 20, after plywood sheathing 86 has been installed, the next
step in the construction according to the instant invention
consists of securing a second layer of foamed plastic insulation
panels to the plywood. This layer composed of panels 112, which are
nominally 4 feet .times. 4 feet square and which, in the preferred
embodiment, may range between 1 and 5 inches thick. The individual
panels here again are installed tightly one against another. This
layer of insulation is covered by a metal sheathing indicated by
the reference numeral 102. This sheathing is made up of plates
which are nominally 3 feet 11 inches square and the 1 inch gaps
(reference numeral 114 in FIG. 21) therebetween are covered by
batten strips 67 and 68 which are approximately 3 inches wide and
one-eighth inch thick. The long edges 110 of the battens 67 and 68
are turned up approximately one-half inch to prevent buckling under
compressive frictional loading during cool-down to resist dynamic
forces when the ship is at sea. The outer layer of the insulation
and the metal sheathing are secured to the plywood structural layer
86 by means of stud screws 104. Screws 104 are provided with
hexheads and have approximately three-fourths inch of wood screw
thread at their ends 113. Thus, the wood screws extend one-eighth
inch beyond the inner surface of the plywood for increased bite. In
the preferred embodiment five of these stud screws are used to
secure each sheathing plate and the immediately adjacent insulation
layer behind it. As may be seen in FIG. 22, one of these stud
screws goes through the hole 116 at the center of the sheathing
plate. This center hole is approximately the same nominal diameter
as the stud screw and, hence, a snug fit is maintained between the
stud screw and the plate at this point. Holes 114 are approximately
one-fourth inch in diameter oversized and are located halfway
between hole 116 and the respective corner of sheet 102. Each of
the five stud screws used to secure sheet 102 is provided with a
washer under its hexhead. Thus, the center stud screws fixes the
position of the sheet 102 while the four other stud screws allow
for small amounts of thermal movement that may take place in
service. The holes through the insulation and into the plywood may
advantageously be drilled in the field at the time of installation
and, hence, do not involve aligning up with predrilled holes in the
insulation or the plywood. This, of course, minimizes installation
difficulties and allows for tight positioning of the outer
insulating panels against one another. It is also to be pointed out
that since stud screws 104 are not affixed to cold tank wall 36,
but to the relatively warmer plywood layer 86, they do not serve as
paths of major heat leaks.
In the preferred embodiment each of the longitudinal batten strips
67 are approximately 7 feet 111/2 inches long, which allows for
one-half inch clearance between the ends of adjacent longitudinal
battens. They are secured by four stud screws, one of which passes
through a hole having substantially the same diameter as the
diameter of the stud screw and this fixes that point of the batten
with respect to the plywood sheathing. The other three holes in the
batten are elongated (not shown) to permit some relative movement
with temperature changes and other slight movements which will
occur in service. The transverse battens 68 are affixed in a
similar manner, thus they too are permitted to undergo
predetermined axial movement. As with the installation of the metal
sheathing layer 102, all of the holes in the second installation
layer in the plywood which must accommodate the screw threads which
hold the battens in place are drilled in the field and, hence,
therefore, here also no matching up of predrilled holes is
necessary.
As clearly shown in FIG. 19, which is a breakaway plan view, all
junctions between the various panels comprising the various layers,
which in turn make up the primary tank insulation system, are
staggered so as to eliminate breakthrough penetration at any
point.
A unique feature of the instant invention, which should be at this
point obvious to one skilled in the art, is the fact that the
insulation system applied to the primary cargo tank may be
dismantled and reassembled without destroying any of the
components. Such a feature would have particular significance if
regulatory bodies should decide to require periodic inspection of
the outer wall of the cargo tank 37.
For a general, overall view of the various components making up
that portion of the installation of the instant invention which is
applied directly to the tank 37, reference should be made to FIG.
23. This figure shows construction details on both outside type
corners, designated 43a, and inside corners such as 43b. This view
also shows a typical construction used at one of the keyways. A
significant detail of the installation construction at an outside
corner such as 43a is that the plywood panel 86 extends over the
rounded corners of the tank to provide for attachment in support of
the insulation and sheathing. Thus, this construction permits the
use of rectilinear insulation panels and eliminates any need for
molded insulation to fit the contours of the tank 37. The void 126
between the curved corner of the tank and the rectangular junction
of the insulation extensions is filled with a suitable loose
insulation such as foam plastic pellets or the like. The resiliency
of the plastic pellets serves to keep the inner insulation panels
tight against the underside of the plywood panels. The construction
details of the inside corners such as 43b may also be readily
appreciated by reference to FIG. 26.
From the foregoing detailed description of the instant invention it
is seen that highly efficient and fail-safe system is provided for
the transportation of liquefied hydrocarbon cargoes such as
liquefied natural gas. The layer of fiberglass encapsulated
insulating panels 51 provided on the interior of the inner hull 52
serves as a liquid and gastight secondary barrier for the cold
cargo in the event that a failure occurs in tank 37 and the
resultant spillage permeates the insulation system which is affixed
thereto. A significant aspect of this invention is the relatively
high temperature of the layer 51 during normal service conditions
due to the insulating effect of the insulation layer on tank 37.
This, of course, reduces the effect of thermal stress cycling and
continued exposure to very low temperatures on the integrity of
layer 51 so that it remains structurally sound and capable of
containing, when called upon to do so, leakage from the primary
container 37.
It should be understood that the specific structures herein
illustrated and described are intended to be representative only,
as certain changes may obviously be made therein without departing
from the clear teachings of the disclosure. For example, while the
insulation affixed to tank 37 has been described as being comprised
of more than one layer, those skilled in the art will readily
appreciate that if desired a single layer could be provided. In the
alternative, more than two layers of insulating panels could also
be affixed to the tank 37. Furthermore, while the invention finds
particular utility in conjunction with shipboard cryogenic
containers, it will also be appreciated that it may be employed to
equal advantage for the construction of relatively fail-safe land
based storage facilities for cryogenic materials. Accordingly,
reference should be had to the following appended claims in
determining the full scope of the invention.
* * * * *