JPS5828235B2 - Method for determining the size of the bone - 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 PREFERRED EMBODIMENTS The present invention relates to a novel structure for forming thermal insulation, particularly the inner thermal insulation, for liquefied natural gas and other cryogenic vessels.

In general, various types of thermal insulation structures for cryogenic vessels have been implemented or proposed, but the term "inner insulation" as used here refers to a structure in which an insulation layer is fixed on the room temperature side and the low temperature surface is installed with almost no constraint, such as a structure in which an insulation layer is attached to the inner surface of a vessel's hull and the cryogenic vessel is stored in the internal space, either as an independent or membrane type.

In this sense, the internal insulation method in which the insulation layer also serves as a low-temperature container and is in direct contact with the loaded cargo liquid is also included in this range.

The object of the present invention is to provide an inner heat insulating layer which uses a material having excellent low-temperature resistance, prevents the inner heat insulating layer from being damaged by thermal stress or external mechanical shock and repeated load, and is highly reliable, has a relatively simple structure, and is inexpensive.

It is yet another object of the present invention to provide an effective internal heat barrier or a heat barrier that also functions as a secondary barrier by employing oil-resistant and liquid-tight materials and structures.

The present invention is characterized in that the heat insulating layer is formed from a rigid urethane foam applied by a spray method, that the material of the rigid urethane foam has a safety factor of 1.5 or more, as defined later, and that the inner surface of the urethane foam is reinforced by adhering a reticulated base material C (hereinafter referred to as mesh) selected from glass fiber, natural fiber, synthetic fiber, etc., with a rubber or plastic adhesive, thus making full use of the excellent insulating performance of the rigid urethane foam and the advantages of in-situ spray foaming, forming an extremely safe heat insulating layer that does not crack even at low temperatures and even ultra-low temperatures.

It is well known that rigid polyurethane foams are generally hardly affected by petroleum-derived hydrocarbons and do not allow these liquids to pass through them unless there are cracks or imperfect pores.

Taking advantage of this property, various low-temperature heat insulation methods have already been proposed, using polyurethane foam itself or in combination with a reinforcing material, or sometimes also serving as a secondary barrier.

For example, JP-A-48-54509 and JP-A-48-8
In publications such as Publication No. 6153, it has been proposed to use various mesh materials, including wire netting, in combination with polyurethane foam. However, in order to actually obtain effective performance, it is necessary to take into consideration the complex relationships between the properties of the rigid polyurethane foam, particularly the changes in properties due to temperature, the various construction methods, the properties of the mesh, the installation method, etc., and serious problems often arise if these factors are not taken into consideration. However, the above-mentioned publications do not provide any examples or explanations regarding these matters.

According to Japanese Patent Application Laid-Open No. 49-47926,
The use of a complex three-dimensional fiber-reinforced spongy plastic (urethane foam) in combination with a permeable liner has been proposed as a thermal insulation layer for cryogenic containers, but it has been stated that the use of a non-fiber-reinforced spongy plastic in combination with a glass mesh bilayer liner alone is inappropriate as a thermal insulation layer for cryogenic containers.

When using plastic foam for heat insulation at low temperatures below -80°C, there are many difficult problems related to the brittle point of plastic. In particular, in an inner heat insulation structure where the two room temperature sides are fixed, large thermal stress is generated on the low temperature side of the heat insulation layer, which not only occurs in static conditions but also when subjected to external mechanical shocks and repeated loads, resulting in further damage such as cracks. Solving this problem was not easy.

Meanwhile, the present inventors have been conducting extensive research into various heat insulating structures, and as a result of a detailed investigation into the relationship between the properties of rigid urethane foam and the reinforcing ability of mesh in the spray foaming method,
In order to solve these problems in internal heat insulation, we have discovered that the most effective method is to appropriately combine and/or select three requirements: a material that can withstand this stress even at low temperatures, a construction method that has little variation in materials, and structural reinforcement. This has led to the invention.

The present invention will now be described in further detail.

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

The thickness achieved by one spray is relatively thin, usually 1
The foam rises approximately perpendicular to the target surface in the form of free foam.

Therefore, the residual stress during foam molding is smaller than that of the injection foaming method.

In addition, since construction can be carried out over a large area with virtually no seams, the material is almost uniform across the width.

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

The spray foaming method itself is a known technique, so a detailed description thereof will be omitted here.

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

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

The term "urethane foam" as used herein includes polyisocyanate foams, such as isocyanurate foam and carbodiimide foam.

Among these, it is not clear what physical properties of materials are suitable as heat insulating materials for ultra-low temperatures such as liquefied natural gas.

However, when low-temperature heat insulation experiments were carried out at 7 ohms with various blends, there was a large difference in the amount of cracks that occurred, making it clear that the properties of the urethane foam itself are of primary importance.

The physical properties representative of the low temperature resistance of a foam are generally considered to be the tensile strength TS of the foam itself, the tensile elongation EB, or their product TSXEB, and their temperature dependences, but these values do not necessarily coincide with the actual experimental results.

After much trial and error, the inventors have found that the following coefficients are useful as important properties in expressing the effectiveness of a foam at low temperatures:

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

The reason for focusing on the vertical direction here is that it has been found that since almost all cracks occur in a direction perpendicular to the heat insulating surface, the ratio of thermal stress in the direction perpendicular to the foaming (parallel to the target surface) to the tensile strength of the foam is important.

This will be called the safety factor.

The thermal stress can be obtained by measuring the magnitude of the force tending to shrink when a foam specimen, both ends of which are fixed at room temperature, is placed in a low-temperature atmosphere.

In addition, the low temperature tensile strength can be determined again by conventional tensile testing using the same equipment.

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

As shown in the figure, a test piece A having a size of 10 (width) x 10 (thickness) x 100 (length, in the upward direction) taken from a sprayed layer of rigid polyurethane foam is placed in an insulating container R and attached between upper and lower crossheads to restrain the longitudinal direction.

D is a load cell, and E and E' are fixtures for fixing the test specimen.

From a separate device, liquid nitrogen and an appropriate amount of air are mixed together to produce cold air at a constant temperature, and the temperature inside the container R is raised from room temperature to -192°C.
Cool to °C.

The thermal stress generated in the test piece A is detected by a load tester.

After about 15 minutes when the temperature inside the container reached -192°C, the thermal stress became substantially constant.

Next, the fixture E is loosened to set the test piece A in a free state, and then the fixtures E and E' are retightened. A load is applied to the test piece while lowering the lower crosshead C, and the tensile strength at -192°C is measured.

Thus the safety factor is calculated as follows:

The reason why the temperature of -192°C was used in particular is that LNG (
This indicates a temperature that can be relatively easily reached using liquid nitrogen (-196°C) for the purpose of application to objects including liquid nitrogen (-162°C).

So it doesn't have to be so strict.

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

In this case, the safety factor is less than 1.

Regarding the relationship between the safety factor and low-temperature resistance, tests were repeatedly conducted at low temperatures, particularly including shocks that would actually be expected, as shown in the examples. As a result, it was found that a certain margin must be added to the values obtained from the small specimens described above, and that values of approximately 1.5 or more are useful, and preferably 2.0 or more.

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

The specific gravity of this skin layer is 2 to 10 times that of the core, and its thickness is 0.1 to 10 cm compared to that of the core, depending on the construction conditions.
The thickness is 3++oa or less, usually about 0.1 mm, and the skin is naturally harder than the core and has a smaller tensile elongation.

In reality, several sprayed layers are stacked, so the properties of the foam combining the skin and core are important, and this must be taken into consideration when measuring the safety factor mentioned above.

The wavy lines in FIG. 1, specimen A, indicate the presence of the epidermis.

In the case of inner heat insulation, the foam itself is required to have a suitable compressive strength, in most cases about 3 to 5 kg/cm3, and for this purpose a density of about 40 kg/m3 or more is usually required.

Although it is generally easy to produce urethane foams of this quality, many of them are subject to high thermal stresses and it is difficult to obtain a desired safety factor.

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

The blending of concentrate ingredients to obtain the desired foam requires special consideration.

In general, rigid polyurethane foams are produced by the semi-prepolymer method or one-shot method using as the main components a polyfunctional polyol having an OH value (C(KO)) of 300 to 8000 (3.5 or more) and an aromatic polyisocyanate, with the addition of foam stabilizers, catalysts, blowing agents such as halogenated hydrocarbons or water, flame retardants, plasticizers, etc. as necessary.

On the other hand, the foam for low temperature has a low OH value of 450 or less and
It is preferable to use a relatively low functionality polyol and a polymeric isocyanate.

The following table shows the physical properties of low-temperature foam, which has a large safety factor, in comparison with those of general foam.

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

On the other hand, since thermal stress is related to the product of the elastic modulus and the linear expansion coefficient, it is possible to create a foam with a relatively high safety factor by using methods to reduce the latter value, such as embedding long glass fibers or premixing short fibers that are close to powder into the resin. However, this requires very complicated operations and poses many problems for practical use.

Yet another requirement is surface reinforcement by 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 substrate:

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

As for the inside insulation, the foam is also cooled with restraints in the width direction, so the reinforcing material must be stronger and have a higher safety factor.

When installed, the part is impregnated with adhesive, so it must be tested in this composite form.

Next, since the surface of the foam produced by spraying is not necessarily smooth, it is preferable to use a foam that is soft and spreads well.

In this sense, a mesh made of a single wire, such as that found in ordinary metal netting, is inappropriate.

Naturally, it is also important that the material be readily available.

If the mesh size is too large, the reinforcement will be insufficient, and if it is too small, it will not fit well with the edge 1, so a glass fiber mesh with 2 to 8 mesh holes is preferable.

For example, Nitto Boseki Co., Ltd.'s glass cloth WC-250°, about 3 μm, strand density 7 strands/25 m
m, square pattern plain weave cloth.

A single thread is made up of several hundred strands of fibers twisted together and has an apparent diameter of about 0.35 mm.

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

Adhesives can be selected from rubber-based adhesives such as Hypalon X, plastic-based adhesives such as polyurethane, epoxy, polyester, urea, and phenolic solvent-based adhesives, and in some cases emulsion-based adhesives.

In the case of internal insulation, the structure is such that it comes into direct contact with the loaded cargo, such as liquefied propane or liquefied natural gas (internal insulation), and it is necessary to assume that there will be an opportunity for it to come into contact (secondary barrier).
Naturally, the material must not be altered by these factors.

One suitable example is a solvent-based chloroprene rubber.

The adhesive method is to first apply a thin layer of adhesive to the foam surface,
When it is half dry, attach the mesh to it to temporarily secure it in place.

Mechanical auxiliary means such as the use of staples are also effective.

A feature of the internal heat insulating layer of this structure is that it is also liquid-tight, but the liquid-tight performance itself resides in the continuously molded sprayed foam layer itself, and the purpose of using the mesh is primarily to reinforce the skin to prevent cracks in the foam, not to form a liquid-tight coating (so-called membrane) for the contained liquid in combination with the adhesive coating.

On the contrary, if a nearly liquid-tight membrane is formed by such means, there is a possibility that liquefied gas may penetrate between the foam and the coating through some route, and the liquefied gas may rapidly gasify as the temperature increases, resulting in back pressure that may cause major damage to the reinforcing layer.

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

In fact, for example, ultra-low temperatures such as liquefied natural gas (about -162°C)
It is actually more difficult to find a material that can form a strong coating film, but selecting a material that satisfies the above conditions is not that difficult.

In general, the low temperature resistance of most adhesives improves significantly when used in combination with glass fibers.

For example, when a cooling test was conducted with liquid nitrogen on the above-mentioned reinforced surface using chloroprene rubber or urethane adhesive, good adhesion between the thread and foam was observed, and many small cracks were observed in the thin layer of adhesive alone between them, confirming the effectiveness of not creating a coating for the purpose of reinforcement alone.

One reason why the minimum mesh size is set to 2 mm is due to the above-mentioned workability limit.

It is sufficient to cut the foam surface smooth prior to bonding only in areas with particularly severe L1.

A preferred example of the application of the heat insulating structure of the present invention is the secondary barrier of a rectangular independent tank type LNG ship that also uses balsa material, the so-called container system.

Specific examples of the structure of the present invention are shown in FIGS.

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

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

It is advisable to apply a primer to the inner surface of the exterior wall prior to spraying the polyurethane to ensure good adhesion.

Chloroprene rubber coating is one suitable example.

Nos. 2, 4, 5, 6 and 7 are thermal insulation layers of rigid polyurethane foam with a safety factor of 1.5 or more laminated by spraying.

The thickness of each layer is 20 mttg on average, and five layers are used for a total of 100 mttg.

Empirically, the spray thickness for one layer is preferably 10 to 25 mm, and the required thickness can be increased or decreased depending on the number of layers.

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

The other layers are similar. 10 indicates the threads of the reinforcing mesh 2 to 8, which are exaggerated in scale for ease of explanation.
It is fixed by.

The space shown in 11 indicates a low temperature area, and may be used in cases where an independent low temperature tank is stored separated by a space, where a membrane tank is installed in contact with the thermal insulation layer, or where the low temperature material being stored is directly in contact with the tank.

The above description shows one embodiment of the present invention, but it goes without saying that various modifications can be made without changing the concept.

For example, to achieve a beautiful inner surface, the inner surface of the reinforcing layer may be covered with a thin sprayed layer of rigid polyurethane foam, or, particularly in the case of membrane tank storage, a top coat of a material that has little to do with thermal insulation properties may be applied to obtain a smooth finished surface.

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 is considered to be a means of further improving safety.

However, since the present invention is characterized by a thorough consideration of the foam material and thus hardly requires such a structure, it is wise to use the simplest structure possible from an economical standpoint.

Next, various experiments were carried out to confirm the effects of the present invention, and specific examples thereof will be presented below.

Example 1: One hole is placed around each of the four peripheries of a steel plate measuring 200 x 1200 x 5 mm (thickness).
Test specimens were prepared by fixing a number of dish-shaped containers to plywood frames measuring 100 mm (thickness) x 100 mm (height), and spraying hard urethane foam into the insides of these containers to a thickness of 15 ken per layer, for a total of 5 layers to a thickness of 75 ken.

For comparison, the experiment was carried out using 90 pieces in total, 10 pieces for each of 9 types of combinations of various materials, structures and cooling temperatures.

The reinforcing material used was the three-joint glass fiber mesh mentioned above, and its periphery was glued and fixed to the frame.

The cooling test was carried out by directly pouring liquid nitrogen (-196°C) into the space above the test specimen for a-e, and filling the space with dry ice (approximately -70°C) for a'-d'.
Time was held.

Furthermore, the impact test was performed using a 11 mm wedge with a width of 7 mm on the tip (φ8) in the presence of liquid nitrogen or immediately after removing the dry ice.
) x approx. 1800 mm (length) steel bar (weight 600 mm)
The sample was dropped onto the surface of the thermal barrier layer from a height of 100 m.

By the way, when there was a mesh, the wedge cut through the mesh to a depth of about 20 mm.

The results are shown in the following table.

(Notes) *1 *2 The "top layer" of rigid polyurethane foam made by Nippon Soflan is indicated by the vertical position of the test specimen and corresponds to the innermost layer in the text.

In the cases of (d) and (e), no cold spots were observed on the rear surface of the steel sheet even after the impact test, and the coloring test after heating confirmed that the liquid was completely sealed.

Furthermore, when the structure (d) was used and tested on a 3.5 x 3.5 m model at low temperature under dynamic repeated loads equivalent to those experienced on a ship for 20 years, it withstood the load adequately.

From the results in the above table, it is clear that even with a material with a safety factor of 2, in the presence of liquid nitrogen at -196°C, bare foam is not perfect as in (C), but if mesh reinforcement is applied only to the surface, it will not only have static resistance but will also withstand severe impact tests as in (ω); even if a similar reinforcement is applied, the purpose will not be achieved if the foam material is not suitable as in (b); and further, in order to pass the impact test, a combination of low-temperature foam and mesh is necessary even at temperatures around dry ice.

Injection foamed foams are more likely to crack at low temperatures than spray foamed foams, even if they are made of the same material, and since it is necessary to create seams in many places, they are completely unsuitable for purposes such as liquid tightness, as is the subject of this invention.

As described above in detail, the present invention relates to a hard urethane foam material,
It provides a very simple and relatively inexpensive structure by skillfully combining construction methods and mechanical reinforcement methods.
It is extremely useful for use as an inner heat insulating layer for transporting or storing low-temperature liquefied gases such as G and LNG.

[Brief description of the drawings]

Fig. 1 is a schematic diagram showing an example of an apparatus for determining a safety factor in the present invention, and Fig. 2 is a partial cross-sectional view showing an example of the structure of the heat insulating layer according to the present invention. Fig. 3 is a partial enlarged view of Fig. 2, Fig. 4 is a partial enlarged view showing another example of Fig. 2, Fig. 5 is a partial cross-sectional view when the heat insulating structure of the present invention is used as a secondary barrier, Fig. 6 is a partial cross-sectional view when the heat insulating structure of the present invention is used in contact with a membrane tank, Fig. 7 is a partial cross-sectional view when the heat insulating structure of the present invention is used as an internal heat insulation, and Fig. 8 is a partial cross-sectional view of a variation of Fig. 5, when balsa wood is also used in part. 1....Tank outer wall, 2, 4.5, 6.7...
...Hard polyurethane foam spray layer, 9...
Adhesive, 10...Reinforcing mesh substrate, 11
...Low temperature region, 21...Independent type cryostat, 22...Membrane type cryostat, 23...
...space, 24...balsa wood.

Claims (1)

[Claims] 1. In an inner heat-insulating low-temperature protection device having a heat-insulating layer formed by a hard polyurethane spray layer, the hard polyurethane foam layer has a safety factor of 1.5 or more as defined by:
The heat insulating structure for a cryogenic container is further characterized in that the innermost surface of the urethane foam layer is reinforced by a layer of a fibrous reticulated base material.