JPS5828235B2 - How can I make a difference? - Google Patents

Abstract

1516150 Insulated gas storage containers NIHON SOFLAN CHEMICAL & ENG CO Ltd and SUMITOMO HEAVY INDUSTRIES Ltd 10 Sept 1975 [20 Sept 1974] 37204/75 Heading F4P [Also in Division B5] A thermally insulated container for liquefied gases comprises a rigid shell lined with a thermal insulation structure comprising at least one layer of a rigid polyurethane foam sprayed in situ over a surface of the shell and a reinforcement therefor, the rigid polyurethane foam having a coefficient of safety according to the formula in which (#) means a direction perpendicular to the foam rise, of not less than 1À5, and the reinforcement comprises a fibrous mesh material having a low elongation in 2-dimensional directions which is applied at least on that surface of the insulation furthest from the shed, which constitutes the cold face of the insulation, for fixedly reinforcing the cold face and which mesh material has a sufficiently high strength against tension and shook at the liquefied gas temperature and a high coefficient of safety. The polyurethane may be produced from a polyol having an OH value of not more than 450 and a functional group content of 3 to 5, and a polymeric aromatic polyisocyanate. The fibrous mesh material may be of linen, rayon, nylon, polyester, glass or asbestos fibres. Bonding between the skin of the sprayed foam and the mesh may be effected using as adhesive rubber, chloroprene, SBR, polyurethane, epoxy, polyester, urea or phenol resin. The outer shell may be of metal or concrete and may be the outer wall of a marine tanker or under-ground tank. A primer, e.g. chloroprene, may be applied to the inner surface of the shell before spraying on the polyurethane foam preferably as a plurality of layers. A lining layer membrane may be applied to the resin forced foam structure. Balsa panels may also be employed in the insulation layer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel structure for forming a heat barrier layer, particularly an inner heat barrier layer, in a low temperature container for liquefied natural gas or other materials.

In general, various types of heat insulation structures for cryogenic containers have been implemented or proposed, and the term "inner heat insulation" here refers to, for example, a structure in which a heat insulation layer is attached to the inner surface of a ship's hull, and the cryogenic container is placed in the internal space. This refers to a structure in which the heat insulating layer is fixed on the room temperature side and the surface on the low temperature side is exposed to new conditions with almost no restraint, as typified by a structure that is housed in a stand-alone type or a membrane type.

In this sense, internal heat insulation systems in which the heat insulation layer also serves as a low-temperature container and are in direct contact with the loaded cargo liquid are also included in this scope.

The purpose of the present invention is to use a material with excellent low temperature resistance, to prevent the inner heat-insulating layer from being damaged by thermal stress or external mechanical shock and repeated loading, to have high reliability, and to have a relatively simple structure. This provides a simple and inexpensive inner heat barrier layer.

Still another object of the present invention is to provide a heat barrier layer that employs oil-resistant and liquid-tight materials and structure and is effective for internal heat protection or as a secondary barrier.

The present invention provides that the heat insulating layer is formed of a sprayed hard urethane foam, that the material of the hard urethane foam has a safety factor of 1.5 or more, which will be defined later, and that it is made of a rubber-based or plastic-based material. The inner surface of 7-ohm urethane is reinforced by bonding a mesh base material C (hereinafter referred to as mesh) selected from glass fibers, natural fibers, synthetic fibers, etc. using an adhesive such as In this way, it takes full advantage of the excellent heat insulating performance of rigid urethane foam and the advantages of spray foaming, and forms an extremely safe heat insulating layer that does not cause cracks even at low temperatures or even ultra-low temperatures. .

It is well known that in general, rigid polyurethane foams are hardly attacked by petroleum-based hydrocarbons and do not allow these liquids to pass through them unless there are cracks or incomplete openings.

Utilizing this property, various low-temperature heat insulation methods have already been proposed in which polyurethane foam itself or polyurethane foam is used in combination with a reinforcing material, or in some cases also serves as a secondary barrier.

For example, JP-A-48-54509, JP-A-48-8
In Publication No. 6153, etc., it has been proposed to use various mesh materials including wire mesh together with polyurethane foam, but in order to actually obtain effective performance, it is necessary to consider the properties of the rigid polyurethane foam, especially the changes in properties due to temperature. Although there are complex relationships between various construction methods, mesh properties, installation methods, etc., and serious problems often occur if these are not taken into consideration, the above-mentioned documents do not contain any examples regarding these matters. etc. are not explained.

. Also, according to Japanese Patent Application Laid-Open No. 49-47926,
It has been proposed to use a three-dimensional complex fiber-reinforced spongy plastic (urethane foam) in combination with a permeable liner as a heat-insulating layer for ultra-low temperature containers. It is stated that it is unsuitable as a heat-insulating layer for containers.

There are many difficult problems related to the embrittlement point of plastic when using plastic foam for heat insulation at low temperatures below -80℃, especially in the case of an inner heat insulation structure where the two sides are fixed at room temperature, the low temperature side of the heat insulation layer is large. It was not easy to solve this problem, as thermal stress is generated, which not only occurs in a static state, but also causes further damage such as cracks due to external mechanical shock and repeated loads.

On the other hand, the present inventors have been conducting research on various types of heat-insulating structures, and as a result of a detailed study of the relationship between the properties of rigid urethane foam in the spray foaming method and the reinforcing ability of mesh,
In order to solve these problems in internal heat insulation, we need three things: a material that can withstand this stress even at low temperatures, a construction method that has little variation in material, and structural reinforcement. The present invention was achieved by discovering that it is most effective to appropriately combine and select certain requirements.

Hereinafter, the contents of the present invention will be explained in further detail.

First, the spray foaming method, which is one of the requirements of the present invention, is a method of obtaining a heat-insulating layer of hard urethane foam by directly spraying a material with a relatively high foaming speed onto the target surface.

The thickness obtained by one spraying is relatively thin and usually 1
It is 0 to 25 m and stands up almost perpendicularly to the target surface in the form of free foam.

Therefore, the residual stress during foam molding is particularly small compared to the injection foaming method.

Moreover, since it can be constructed virtually seamlessly over a wide area, the material quality in the width direction is almost uniform.

These two properties are particularly beneficial in low temperature insulation, which is subject to strong thermal stress during use.

Since the blow foaming method itself is a well-known technique, detailed explanation will be omitted here.

Next, we will discuss the other requirement, which is the foam material.

The properties of urethane foam can vary widely, from soft to hard, depending on the composition of its raw materials.

The term urethane foam herein includes polyisocyanate foams, ie, incyanurate foams, carposiimide foams, and the like.

Among these materials, it is largely unknown which materials have physical properties that are suitable as heat insulating materials for ultra-low temperatures such as liquefied natural gas.

However, when conducting low-temperature heat protection experiments using various combinations of 7 ohms, there were large differences in the amount of cracks generated, so it is clear that the properties of the urethane foam itself are of primary importance.

Common sense suggests that the tensile strength TS of the foam itself, the tensile elongation EB, or their product TSXEB, and the temperature dependence of these are the physical properties that represent the low temperature resistance of the foam. does not necessarily match the actual experimental results.

After repeated trial and error, the inventors have found that the following coefficient is useful as an important property representing the effectiveness of the foam at low temperatures.

However, I indicates the case where a force perpendicular to the foaming direction is applied.

The reason why we chose the vertical direction here is that almost all cracks occur perpendicular to the insulation surface, so the ratio of the thermal stress in the direction perpendicular to the foaming direction (parallel to the target surface) and the tensile strength of the foam is This is because it turned out to be important.

We will call this the safety factor.

Thermal stress can be obtained by measuring the magnitude of the force that causes contraction of a foam specimen fixed at both ends at room temperature when placed in a low-temperature atmosphere.

Also, the low temperature tensile strength can be determined again by a conventional tensile test using the machine 1.

FIG. 1 shows an example of a device for determining this safety factor.

As shown in the figure, a sample A of 10 (width) x 10 (thickness) x 100 (length, upward direction) sampled from a sprayed layer of rigid polyurethane foam was placed in a heat-insulating container R and placed between the upper and lower crossheads. Attach it to restrain it in the length direction.

D is a load certifier (load cell), and E and E' are specimen fixing jigs.

The temperature inside the container R was raised from room temperature to -192° by introducing cold air that had been made by mixing liquid nitrogen and an appropriate amount of air to a constant temperature from a separately prepared device.
Cool to ℃.

The thermal stress generated in specimen A is detected by a load verification device.

The thermal stress becomes approximately constant 15 minutes after the temperature inside the container reaches 1192°C.

Next, loosen the fixing jig E to make the specimen A free, then retighten the fixing jigs E and E', apply a load to the specimen without lowering the lower crosshead C, and measure the tensile strength at -192°C. Measure.

The safety factor is thus calculated as follows.

The reason for using a temperature of -192℃ is that LNG (
This indicates a temperature that can be relatively easily reached using liquid nitrogen (-196°C) for the purpose of using it for objects including -162°C.

Therefore, it does not need to be so strict.

In many cases, foams with poor low temperature resistance crack and break even when cooled to -192°C.

The safety factor in this case is 1 or less.

Regarding the relationship between the safety factor and low temperature resistance, as a result of repeated tests at low temperatures, especially including shocks that are expected in reality, as shown in the examples, there is a certain degree of margin in the values obtained from the small specimens mentioned above. It was found that a value of 1.5 or more is useful, and preferably a value of 2.0 or more.

On the other hand, a skin with a higher density than the inner core is formed on the surface of each layer of the sprayed foam.

The specific gravity of this skin layer is 2 to 10 times that of the core, and its thickness is 0.2 to 10 times that of the core, which is 10 to 25 times thicker, depending on the construction conditions.
It is less than 3++ oa, usually about 0.1 mm, and this skin is naturally harder than the core and has a lower tensile elongation.

Since several sprayed layers are actually stacked, the properties of the foam that integrates the skin and core are important, and this must be taken into account when measuring the safety factor mentioned above.

The wavy line in specimen A in FIG. 1 indicates the presence of epidermis.

For internal heat insulation, the foam itself is required to have a suitable compressive strength, in most cases about 3 to 5 kg/cni, and for this purpose, a density of about 40 kg/m@3 or more is usually required.

Although it is generally easy to make urethane foams of this quality, many of them have large thermal stress, making it difficult to obtain a desired safety factor.

The material used in the present invention has a relatively high tensile elongation rate for a hard 7 ohm.For example, the tensile elongation rate of a general foam at room temperature perpendicular to the foaming direction is 3 to 7, whereas the above-mentioned low temperature foam has a low tensile elongation rate. Many are 8, and most are 10.
% or more, and it can be said that 7 ohm, which has a low elastic modulus compared to the density, is suitable for the above purpose.

Special consideration must be given to the formulation of the components of the concentrate to obtain the desired form.

In general, rigid polyurethane foam is mainly composed of a polyfunctional polyol with an OH value (C■KO Luk) of 300 to 80003.5 or higher and aromatic polyisocyanate, and optionally foam stabilizers, catalysts, and halogenated polyols. It is made by a semi-prepolymer method or a one-shot method using a blowing agent such as hydrocarbon or water, a flame retardant, a plasticizer, etc.

On the other hand, the foam for low temperature has a low OH value of 450 or less, and
Preferably, polyols of relatively low functionality and polymeric incyanates are used.

The following table shows the physical properties of low-temperature foams with large safety factors in comparison with those of general foams.

3-7 8-20 Tensile elongation at room temperature (1) - 4.5-15 3.5-13 at 192°C
Tensile strength ■, resistance = (Jj room temperature → -192℃ 5~15 1.0~8.5
Thermal stress (Y) Uotdyama ■ Safety factor -1.0 or less 1.5 to 3.5 (1) (Note) (1); Load perpendicular to the foaming direction ω) 2 Load parallel to the foaming direction As mentioned above, the inventors have obtained a foam with a large safety factor mainly in the direction of lowering the elastic modulus by improving the resin composition.

On the other hand, thermal stress is related to the product of elastic modulus and linear expansion coefficient, so there are ways to reduce the latter value, such as embedding long glass fibers or premixing short fibers similar to powder into resin. Although it is possible to create a form with a high kana safety factor, it requires very complicated operations and there are many problems in practical use.

Yet another requirement is surface reinforcement with mesh.

This material can be selected from natural fibers such as hemp, synthetic fibers such as rayon, nylon, and polyester, and inorganic fibers such as glass and asbestos.

The following points should be taken into consideration when selecting the base material:

First, the material itself must have sufficient tensile and impact strength even at low temperatures.

In the case of inner heat insulation, the foam is also mentioned, and similarly, the width direction is restricted by 1. Since the foam is cooled, the reinforcing material must have even higher strength and a higher safety factor.

Since it is impregnated with adhesive during installation, it is necessary to test this composite form.

Next, when spraying, since the surface of the foamed foam is not necessarily smooth, it is preferable to use something that is soft and can fit well on the surface.

In this sense, a mesh constructed of single wires, such as those found in ordinary metal mesh, is inappropriate.

Naturally, it is also an important requirement that the material be easily available.

If the size of the mesh is too large, the reinforcement will be insufficient, and if it is too small, it will be difficult to fit into the mesh 1. Therefore, a glass fiber mesh with mesh size between 2 and 8 is preferable.

For example, glass cloth WC-250, manufactured by Nitto Boseki Co., Ltd. (3rd stock), about 3u, thread density 7 strands/25 m
m, square pattern plain weave cloth is available.

One thread is made up of several hundred fibers twisted together, and has an apparent diameter of about 0.35 mm.

Chloroprene and SBR are used to bond the sprayed foam skin to the mesh.

A rubber-based adhesive such as Hypalon X, a plastic-based adhesive such as polyurethane, epoxy, polyester, urea, or phenol, solvent-based adhesive, or emulsion-based adhesive in some cases can be selected.

For internal heat insulation, it is necessary to assume that the structure is such that it will come into direct contact with the loaded cargo, such as liquefied propane or liquefied natural gas (internal heat insulation), or that there will be a chance of contact with it (secondary barrier).
Naturally, the material must not be altered by these substances.

One suitable example is solvent-borne chloroprene rubber.

The adhesive method is to first apply a thin layer of adhesive to the foam surface,
Attach the mesh when it is half dry and temporarily secure it.

Mechanical aids, such as the use of staples, are also effective.

The internal heat-insulating layer of this structure is characterized by being liquid-tight, but the liquid-tight performance itself lies in the sprayed foam layer itself, which is continuously molded, and the purpose of using mesh is simply to protect the foam. In reinforcing the skin to prevent cracks, the purpose is not to form a liquid-tight coating (so-called membrane) for containing liquid in coexistence with the adhesive coating.

Rather, if a nearly liquid-tight membrane is formed by such a method, there is a possibility that liquefied gas will enter between the foam and the coating through some route, and as the temperature rises, the liquefied gas will rapidly gasify, resulting in There is a risk of major damage to the reinforcing layer due to back pressure.

To avoid this phenomenon, the adhesive should be made of a material that does not form a tough film at low temperatures and allows gas to escape easily.

In fact, for example, ultra-low temperature (approximately -162℃) such as liquefied natural gas
It is rather difficult to find a material that forms a strong coating film, but it is not so difficult to select a material that satisfies the above conditions.

In general, the low temperature resistance of many adhesives is significantly improved when they coexist with glass fiber.

For example, a cooling test with liquid nitrogen on the above-mentioned reinforced surface using chloroprene rubber or urethane adhesive showed good adhesion between the thread and foam, and the thin adhesive layer between them showed many small cracks. It was possible to confirm the effect of not creating a film for reinforcement purposes only.

One of the reasons why the minimum mesh size is set to 2 mm is due to the above-mentioned limit of machinability.

It is sufficient to smoothen the foam surface prior to adhesion, especially in areas where Lll is severe.

A preferable example to which the heat insulation structure of the present invention is applied is a so-called conte type secondary barrier of a rectangular independent tank type LNG ship that also uses balsa wood.

Examples of specific structures of the present invention are shown in FIGS. 2, 3, and 4.

In the figure, reference numeral 1 denotes a tank outer wall made of metal, concrete, etc., which corresponds to the hull of a ship or the outer shell of a double-structure above-ground or underground tank.

Therefore, the outer surface of this wall (downward in Figure C) is in contact with room temperature air, seawater, or soil.

It is desirable to prime the inner surface of the outer wall to improve adhesion prior to spraying polyurethane.

A chloroprene rubber coating is one suitable example.

2, 4, 5.6 and 7 are heat insulating layers of rigid polyurethane foam laminated by spraying and having a safety factor of 1.5 or more.

The average thickness of one layer is 20 mttg, and the case is 5 layers, totaling 100 layers.

Experience has shown that the spraying thickness of one layer is in the order of 10 to 25, and the required thickness can be increased or decreased depending on the number of layers.

A relatively hard skin layer 3 exists on the surface of the first layer 20.

The same applies to other layers below. 10 is an exaggerated scale for ease of explanation, but it shows each thread of the reinforcing mesh of the 2nd to 8th mesh, and the adhesive 9 is attached to the skin layer 8 of the innermost layer 7.
It is fixed by.

The space shown in 11 indicates the low-temperature region, and when an independent low-temperature tank is housed across the space, when a membrane tank is installed in contact with a heat-insulating layer, or when a low-temperature tank is directly stored. There are cases where substances come into contact.

Although the above description shows one embodiment of the present invention, various changes can be made without changing the concept.

For example, to give the inner surface a beautiful finish, the inner surface of the reinforcing layer may be covered with a thin sprayed layer of hard polyurethane foam, or, especially in the case of membrane tank storage, to obtain a flat finished surface, the inner surface of the reinforcing layer may be covered with a material unrelated to heat insulation performance. This includes applying a finishing coat.

On the other hand, providing a similar reinforcing layer not only on the surface of the innermost layer but also on the surfaces of the second and third sprayed layers from the inside can be considered as a means to further improve safety.

However, the present invention is characterized in that the material of the foam is thoroughly considered and there is almost no need for it, so it is wise to keep the structure as simple as possible from the viewpoint of economy.

Next, various experiments were conducted to confirm the effects of the present invention, and specific examples thereof are listed below.

Example 1 1 for every 4 circumferences of a steel plate of 200 x 1200 x 5 mm (thickness)
Hard urethane foam was sprayed on the inside of a number of dish-shaped containers prepared by fixing plywood frames of 0 mm (thickness) x 100 mm (height) to a thickness of 15 mm per layer, a total of 5 layers of 75 mm. A specimen was prepared with the attached.

For comparison purposes, a total of 90 experiments were conducted, combining various materials, structures, and cooling temperatures, with 10 of each type and 9 types.

The reinforcing material used was the glass fiber mesh for the third eyelet mentioned above, and the area around it was glued and fixed to the frame.

In the cooling test, liquid nitrogen (-196°C) was directly injected into the upper 25-degree space of the specimen for a-e, and dry ice (approximately -70°C) was filled for a'-d'. Yes, at least 2
Holds time.

Furthermore, the impact test was carried out using 11 in the presence of liquid nitrogen or 8 (φ
) x approx. 1800mm (length) steel rod (weight 600@) 1
It was dropped onto the surface of the heat barrier layer from a height of m.

By the way, when there was a mesh, the wedge cut through the mesh of that width, and the penetration depth was about 20 mm.

The results are shown in the table below.

(Note) *1 *2 Made by Nippon Soflan, hard urethane foam. The top layer is shown in the vertical relationship of this specimen and corresponds to the innermost layer in the text.

Regarding (d) and (e), no cold spots were generated on the back surface of the steel plate even after the impact test, and it was confirmed that the liquid seal was perfect even in the coloring test after increasing the temperature.

Furthermore, when the structure of (d) was tested using a 3.5 x 3.5 m model at low temperatures and subjected to 20 years of dynamic load on a ship, it was able to withstand sufficiently.

From the results in the above table, even with a material with a safety factor of 2, the bare foam is not perfect in the presence of liquid nitrogen at -196°C, as shown in (C), but if only the surface is mesh-reinforced (as shown in ω), the static In addition to durability, it must also withstand severe impact tests, and even if similar reinforcement is applied, the purpose will not be achieved if the foam material is not suitable as shown in (b).In order to satisfy the impact test, dry The relationship is clear, such as the need for a combination of low-temperature foam and mesh even at temperatures comparable to ice cream.

Injection-foamed foams are more likely to break at low temperatures than spray-foamed foams even if they are made of the same material, and seams must be made at multiple locations, so they are completely unsuitable when the purpose of liquid-tightness is the object of the present invention. It is.

As detailed above, the present invention is made of hard urethane foam material,
It provides an extremely simple and relatively inexpensive structure through a clever combination of construction methods and mechanical reinforcement methods, and LP
It is extremely useful for use as an inner heat-insulating layer of tanks for transporting or storing low-temperature liquefied gases such as G, LNG, etc.

[Brief explanation of the drawing]

FIG. 1 is an implicit explanatory diagram showing an example of a device for determining a safety factor according to the present invention, and FIG. 2 is a partial sectional view showing an example of the structure of a heat-insulating layer according to the present invention. Fig. 3 is a partially enlarged view of Fig. 2, Fig. 4 is a partially enlarged view showing another example of Fig. 2, and Fig. 5 is a partial cross section when the heat insulating structure of the present invention is used as a secondary barrier. Figure 6 is a partial cross-sectional view when the heat-insulating structure of the present invention is used in contact with a membrane tank, and Figure 7 is a partial cross-sectional view when the heat-insulating structure of the present invention is used as internal heat insulation. FIG. 8 is a modification of FIG. 5, and shows a partial sectional view when balsa wood is used in combination. 1... Tank outer wall, 2, 4.5, 6.7...
...Hard polyurethane foam spray layer, 9...
... Adhesive, 10 ... Reticulated base material for reinforcement, 11
・・・・・・Low temperature range, 21・・・・Independent type low temperature container, 22・・・・Membrane type low temperature container, 23・
...Space, 24...Balsa wood.

Claims (1)

[Scope of Claims] 1. In an inner heat-insulating type having a heat-insulating layer formed by a sprayed hard polyurethane layer, the hard urethane foam layer has a safety factor of 1.5 or more defined by: have,
A heat-insulating structure for a low-temperature container, characterized in that the innermost surface of the urethane foam layer is reinforced by a layer of a fibrous network base material.