U.S. patent number 3,861,021 [Application Number 05/367,722] was granted by the patent office on 1975-01-21 for method of constructing a low temperature liquefied gas tank of a membrane type.
This patent grant is currently assigned to Bridgestone Liquefied Gas Company, Ltd.. Invention is credited to Katsuro Yamamoto.
United States Patent |
3,861,021 |
Yamamoto |
January 21, 1975 |
METHOD OF CONSTRUCTING A LOW TEMPERATURE LIQUEFIED GAS TANK OF A
MEMBRANE TYPE
Abstract
A method of constructing a low temperature liquefied gas tank of
the membrane type equipped with a doublelayered inner membranous
vessel composed of outside and inside membranous vessels, said
double-layered inner membranous vessel being pre-constructed
separately from the outer rigid vessel which is adapted to receive
said inner vessel, said double-layered inner membranous vessel
being thereafter mounted into said outer vessel, characterized in
that a vacuum is applied to the space formed between said outside
and inside membranous vessels in the process of mounting said inner
vessel into said outer vessel.
Inventors: |
Yamamoto; Katsuro (Tokyo,
JA) |
Assignee: |
Bridgestone Liquefied Gas Company,
Ltd. (Tokyo, JA)
|
Family
ID: |
13461542 |
Appl.
No.: |
05/367,722 |
Filed: |
June 7, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Jul 17, 1972 [JA] |
|
|
47-71471 |
|
Current U.S.
Class: |
29/455.1;
114/74A; 220/560.08; 29/446; 220/901; 220/560.15; 220/592.27 |
Current CPC
Class: |
F17C
3/025 (20130101); B63B 25/16 (20130101); Y10T
29/49863 (20150115); F17C 2203/03 (20130101); F17C
2270/0105 (20130101); F17C 2270/011 (20130101); F17C
2221/035 (20130101); Y10S 220/901 (20130101); Y10T
29/49879 (20150115); F17C 2223/0161 (20130101) |
Current International
Class: |
F17C
3/02 (20060101); B63B 25/00 (20060101); B63B
25/16 (20060101); F17C 3/00 (20060101); B21d
039/00 () |
Field of
Search: |
;29/157R,455,446
;220/9A,9LG,9C ;114/74R,74A,74T,.5T |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lanham; C. W.
Assistant Examiner: Crane; Dan C.
Attorney, Agent or Firm: Stewart and Kolasch, Ltd.
Claims
I claim:
1. In a method of constructing a low temperature liquefied gas tank
of the membrane type, said tank comprising a rigid outer vessel, a
compression-resistant heat insulating layer provided at the inside
of said outer vessel, and a double-layered inner membranous vessel
including outside and inside membranous vessels disposed at the
inside of said heat insulating layer, said method comrising the
steps of constructing said outer vessel and said heat insulating
layer so as to provide a hold space having an opened upper portion
for receiving said double-layered inner membranous vessel, said
double-layered inner membranous vessel being constructed separately
from said outer vessel and heat-insulating layer, and thus outside
of said hold space, and thereafter mounting said double-layered
inner membranous vessel into said hold space, the improvement which
comprises applying a vacuum to the space formed between said
outside and inside membranous vessels in the process of mounting
said double-layered inner membranous vessel into said hold space
wherein said outside and inside membranous vessels are caused to
contact each other substantially over the entire surface thereof,
thereby increasing the rigidity of the double-layered inner
membranous vessel.
2. The method according to claim 1, wherein said double-layered
inner membranous vessel is pre-constructed as an inner vessel
assembly including a rigid carrying structure provided above said
double-layered inner membranous vessel.
3. The method according to claim 2, wherein top panel portions of
said outside and inside membranous vessels are supported by
cantilevers firmly mounted to said carrying structure when said
inner vessel assembly is suspended.
4. The method according to claim 2, wherein bottom portions of said
outside and inside membranous vessels are suspended by suspension
means extending from said rigid carrying structure to the bottom
portion of the inside membranous vessel.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of constructing a low
temperature liquefied gas tank, and more particularly a method of
constructing a low temperature liquefied gas tank of the membrane
type for containing low temperature liquefied gases such as
petroleum gases which are in a gaseous state at room temperature
and can be liquefied by being cooled down under atmospheric
pressure.
2. Description of the Prior Art
A tank of this kind is generally composed of a rigid outer vessel,
a compression resistant heat insulating layer provided at the
inside of said outer vessel, and an inner membranous vessel
provided further at the inside of said heat insulating layer. The
inner membranous vessel is made of a thin plate of low temperature
resisting materials and adapted to be flexibly deformed to come in
close contact with the inner surface of the heat insulating layer
when the tank is loaded with liquefied gases in order to transmit
the internal pressure exerted by the liquefied gases to the outer
vessel by way of the compression resistant heat insulating layer so
that the load of the tank is finally supported by the outer
vessel.
A tank of this kind requires an additional secondary barrier wall
for temporarily checking a leakage of the liquefied gases in case
the leakage has occurred in the inner membranous vessel. Since such
a secondary barrier wall is required to have the properties of
resisting hydraulic load, resisting low temperature and of liquid
tightness, it requires highly expensive materials and complicated
structures.
To meet with the conditions required of the secondary barrier wall,
it has been already proposed to provide a secondary membranous
vessel at the outside of the membranous inner vessel to form as a
whole a double-layered inner membranous vessel.
In the case of a low temperature liquefied gas tank equipped with
the double-layered inner membranous vessel, if the tank is
constructed in a manner of first constructing the outer vessel and
the heat insulating layer, and thereafter constructing the
double-layered membranous vessel within the tank, the latter
requiring a relatively long period of construction, the overall
period of construction is very much extended, thereby increasing
the overall cost of the tank. In view of such a disadvantage, it is
also proposed to construct the membranous vessel separately at the
outside of the rigid outer vessel and to mount the pre-constructed
inner membranous vessel into a hold space prepared in the outer
vessel and adapted to receive the same. However, when the
double-layered inner membranous vessel is to be pre-constructed and
mounted into the hold space formed in the outer vessel, the outside
and inside membranous vessels must be temporariy reinforced by a
proper reinforcing frame. Such a reinforcing frame requires a
complicated structure and increases the weight of the assembly
including the outside and inside membranous vessels, requiring a
heavy crane for suspending and mounting the same and thus
increasing the overall cost of the construction.
SUMMARY OF THE INVENTION
Therefore, it is the object of this invention to conquer the
abovementioned difficulties in the conventional methods of
constructing a low temperature liquefied gas tank equipped with a
double-layered inner membranous vessel and to provide a method to
efficiently mount the pre-constructed double-layered inner
membranous vessel into the hold space formed in the outer vessel by
utilizing a particular structure of a pre-constructed
double-layered inner membranous vessel formed of two gas-tight
membranes one enclosing the other in substantially close contact
therewith.
The abovementioned object is accomplished, according to this
invention, by applying a vacuum to a space left between the outside
and inside membranous vessels of the pre-constructed double-layered
inner membranous vessel in the process of mounting the same into
the hold space formed in the outer vessel.
By applying a vacuum to the space left between the outside and
inside membranous vessels, the two membranous vessels come in close
and firm contact with each other and thus act as a single
membranous vessel having so much increased rigidity that the
pre-assembled double-layered inner membranous vessel can be readily
suspended and mounted into the hold space formed in the outer
vessel without the requirement of utilizing complicated reinforcing
frames.
BRIEF DESCRIPTION OF THE DRAWING
The accompanying drawing illustrates the manner of performing the
method of this invention applied to the construction of a low
temperature liquefied gas tank of a membrane type having a
double-layered inner membranous vessel incorporated in a tanker
ship.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the following, this invention will be described in more detail
with respect to the preferred embodiment and with reference to the
accompanying drawing.
The drawing shows a construction process of mounting an inner
vessel of the double-layered membranous structure into a hold space
of a tanker ship, wherein a dual-walled hull 1 including an inner
wall 1a is lined with a compression resistant heat insulating layer
2 over the inside surface thereof to provide a hold space 3 opened
at the upper portion thereof. Such a ship body generally designated
by reference numeral 4 is constructed separately from an inner
vessel assembly generally designated by reference numeral 5.
The heat insulating layer 2 may be made of a material having by
itself compression resisting characteristics such as hard
polyurethane foam as an organic material or foamed concrete as an
inorganic material. The inner surface of the insulating layer is
preferably covered with a protecting plate 23 made of plywood, etc.
Alternatively, the heat insulating layer 2 may be made as a
composite structure including a framework made of wood, etc., the
space left therein being filled with pealite powder, etc. to
provide as a whole a compression resistant heat insulating
layer.
The inner vessel assembly 5 comprising a double-layered membrane
structure composed of an outside inner membranous vessel 6 and an
inside inner membranous vessel 7 is constructed separately from and
preferably in parallel with the construction of the ship body 4.
The outside and inside inner vessels 6 and 7 are made of thin
plates of low temperature resisting materials such as nickel steel,
stainless steel, aluminum, etc., and the two inner vessels may have
a same thickness or may have difference thicknesses so that one is
thinner than the other.
Above the inner vessel assembly 5, there is provided a carrying
structure generally designated by reference numeral 11 including a
tank cover 8 of a rigid structure, a heat insulating layer 9
provided at the underside of the cover 8 and a protecting plate 10
covering the side and lower surfaces of the heat insulating layer
9. The tank cover 8 is provided with a rigid dome 12 at a central
portion thereof. Top panel portions 6a and 7a respectively of the
outside and inside inner vessels 6 and 7 are positioned to follow
the underside surface of the protecting plate 10 and are
fluid-tightly fixed to a flange 13 mounted at a lower portion of
the dome 12. From the lowermost end portion of the rigid dome 12
are radially extended cantilevers 14 adapted to hold the top panel
portions of the inner vessels from falling down.
The inner vessel assembly 5 under construction is held in a
properly self-standing condition by the carrying structure 11 being
supported by proper supporting means (not shown), so as not to
cause any buckling of the inner vessels due to their own gravity.
The inner vessel assembly 5 thus constructed is attached with a
conduit 16 adapted to open to the space formed between the outside
and inside inner vessels via an opening 15 formed in either of the
outside or inside inner vessel according to the convenience of
mounting the conduit 16.
The conduit 16 is connected to a vacuum device 18 such as a vacuum
pump by way of a pipe 17 made of a flexible material such as
rubber, and the air filling a cavity 19 formed between the outside
and inside inner vessels 6 and 7 is exhausted. As the air is
exhausted, the two inner vessels 6 and 7 come in close and firm
contact with each other. Then the inner vessel assembly 5 is
suspended by applying wire ropes 20 to the carrying structure 11
and by suspending the wire ropes by a crane 21. Then the inner
vessel assembly is brought to a position just above the hold space
3 and is lowered and mounted into the hold space. When the inner
vessel assembly 5 is regularly positioned in the hold space, the
tank cover 8 is fixed to the hull 1 by welding or other proper
fastening means.
When the inner vessel assembly 5 is suspended by holding the
carrying structure 11, the cantilevers 14 support the top panel
portions of the inner vessels, whereby stress concentration
occurring at the flange 13 where the weight of the inner vessel
assembly would be concentrated is avoided. The cantilevers 14 may
also support a bottom portion 7b of the inside inner vessel 7 by
means of suspension means 22. In this case, since the outside and
inside inner vessels are firmly stuck to each other due to the
vacuum action, the two inner vessels are supported as a unitary
body by suspending only the bottom portion 7b of the inside inner
vessel 7. The conduit 16 may be provided with a valve so that it is
preserved after the completion of the mounting process to be used
as a means for detecting leakage of the inside inner vessel.
The effects and advantages of the method of constructing a low
temperature liquefied gas tank of a membranous type according to
this invention are summarized as follows:
1. Since the inner vessel assembly and an outer vessel assembly
such as the ship body can be constructed separately in parallel so
that the two construction processes do not interfere with each
other, the overall construction period of the tank is very much
shortened.
2. By applying vacuum to the space formed between the outer and
inner vessels prior to the mounting process of the inner vessel
assembly, the inner vessel assembly can be temporarily provided
with an increased rigidity to be able to hold its space under
suspension and thus can be easily mounted into the outer vessel
assembly.
3. In the process of mounting the inner vessel assembly into the
outer vessel assembly, no reinforcing means such as a supporting
frame is required thereby shortening, the construction period and
lowering the construction cost.
4. After the inner vessel assembly has been mounted in the outer
vessel assembly, test gases are introduced inside the inner vessel
and the gases filling the space formed between the outer and inner
vessels are extracted to test the fluid-tightness of the inner
vessel. In this case, the conduit means provided for exhausting
gases from the space is used since it has been preserved for this
purpose.
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