WO2006130019A1

WO2006130019A1 - Process and system for thermal insulation of cryogenic containers and tanks

Info

Publication number: WO2006130019A1
Application number: PCT/NO2006/000203
Authority: WO
Inventors: Anstein SØRENSEN
Original assignee: Ti Marine Contracting
Priority date: 2005-05-30
Filing date: 2006-05-30
Publication date: 2006-12-07
Also published as: CN101278148A; JP2008542651A; KR20080047321A; NO20052599D0

Abstract

An insulation system for cryogenic containers and tanks comprising at least dual layered insulation panels with groove-and-ridge cooperating assembly structures as well as a groove for injecting a fluid insulation material into the panels provides an improvement for insulating such containers and tanks.

Description

PROCESS AND SYSTEM FOR THERMAL INSULATION OF CRYOGENIC

CONTAINERS AND TANKS

The present invention concerns a process and a system for thermal insulation of cryogenic containers and tanks as well as an insulation plate suitable to be used for such an insulation system and process.

Background for the invention

When transporting low-boiling fluids such as gases in a liquid state, e.g. liquid ammonia, helium, hydrogen, oxygen, nitrogen, methane, ethane, propane, etc., whereof many have a low boiling point and thus will be present in a gaseous state under standard conditions (20°C, 760 mm Hg), it is advantageous to cool these fluids to as low a temperature as possible to bring them into a liquid form and thereby facilitate their transport in larger quanta since liquids require significantly smaller volumes than the same mass in a gaseous state. The problem with such transportation is, however, that if the transport containers are not insulated very well, much of the fluids will disappear through so-called "boil-off, and it is thus very important to insulate such containers and tanks very well thermically. The temperature interval for such cryogenic fluids will lie in the interval -50 to -273°C, preferably -100 to -250ºC, more preferred -125 to - 200°C. The transport temperatures for relevant fluids that may be stored in such tanks, will be at or below the boiling temperatures for such fluids, as explained supra. The insulation material that is used for such insulation must be able to cope with and withstand a very steep thermal gradient since there will exist temperatures very near the boiling point for the relevant fluid at the surface facing towards the container, and ambient temperatures at the surface facing away from the container. Additionally, such an insulation material ought to display a continuous layer around the container providing as few points of temperature transfer to/from the surroundings as possible.

On account of pressure considerations, but also on account of the most favourable volume-to-surface ratio, it is advantageous to transport such fluids, as mentioned supra, in spherical containers (even if the process and system according to the present invention not necessarily is limited to such a shape since also other shapes such as cylindrical, prismatic and spheroidal or even cubical container may be relevant). The problem with such a geometrical design of a container is that the insulation must be adaptable to a surface that is curved in three dimensions (while the side surface of a cylinder will curve in two dimensions and the side surface of a cube will be flat). An isolation system for cryogenic containers as explained supra, should accordingly also be adaptable for all of these types of geometrical shapes.

Prior art

Among Relevant prior art there is known from US patent 3.948.406 a storage container for storing liquefied gas at sub-zero temperatures with a thermally insulating lining consisting of a matrix of cells made of an insulating material and also an insulating material in the joints between the matrix cells, preferably polyurethane. It is also disclosed a method for forming such a lining. The lining according to this prior art is by forming the layer in situ as the lining is built up by applying plymerisable or curable polymeric composition under and between and over blocks of the selected thermally insulating material as they are laid, the polymerisable composition constituting a kind of mortar which is then polymerised and/or cured in situ.

From US patent 3.420.396 there is known a thermally insulated tank consisting of a corrugated wall and insulating blocks fitted in an abutting fashion into the inwardly directed corrugations of the outer wall of the cntainer.

JP patent discloses a heat-insulating structure for a cylindrical cryogenic tank reducing the amount of bending moment through the maximum bending moment acting on stud blocks located near the boundary between the semi-spherical part of the cylindrical tank and the cylindrical body of the tank. The structure apparently is formed by abutting sections of insulating material being placed in a laminated fashion with a wire net in the middle position between the laminated layers and being provided with a synthetic foaming resin body as a binder.

Previously it has been common to add a thermal insulation material in the form of a strip that has been wound about spherical containers continuously whereby the joint area between each winding of such a strip has had to be glued or welded to each other butt-ended in the edge area to ensure that the insulation material becomes continuous on the surface of the container (see supra).

This is illustrated in Fig. 1.

Such a strip has normally been placed on the surface of the container in one single layer. The material in such an insulation material has normally been polystyrene that is commonly used as a material for thermal insulation because it is light-weight and easy to produce. However, the present invention is not limited to such an insulation material.

Also plates of insulating material have been used in the form of a single plate layer for insulating cryogenic containers. Prior art insulation plate solutions are depicted in Figure 2. This technique places great demands to tolerances in the production of plates (small tolerances). The joining of the plates during installation requires the use of a mould and the surfaces require post-treatment subsequent to moulding/casting.

On account of more strict regulations concerning transport of low-boiling fluids, one single layer of such insulating materials is, however, no longer considered as adequate. One single addition of a further layer of an insulating material in the form of a strip as explained supra, is not economically feasible, and thus there has arisen a problem concerning adequate insulation of such cryogenic containers and tanks.

The present invention aims in one aspect at solving this problem.

Disclosure of the present invention

In the system and process according to the present invention for isolating cryogenic containers, there is used plates of e.g. expanded or extruded polystyrene (EPS), even if other materials with insulating properties and/or foaming properties for creating an insulating foam material are possible. Examples of such materials are foamed polyethylene, expanded polystyrene and foamed polyurethane. Such plates, when they are present as flat surfaces, in a size adapted to the curvature of the surface that is to be insulated since they should not give a distance to the surface of the cryogenic container that is larger than 15 mm, and they will preferably lie flat against the container wall. Such a distance will not be limiting all the same, since air is a good insulating material. The plates may also be produced with a curvature adapted to the surface to which they are to be mounted, but this is not preferred since this will increase the price of the plates and make their production more cumbersome. It is then more preferred to make the plates flat, but with smaller dimensions if the container to be covered also has small dimensions.

Typical clearing distances are indicated in Figure 3 depicting an embodiment of the system according to the present invention. The numbers in the figure all relate to mm. Also the structure of the insulation therein is applicable to any tank radius. One embodiment of the plates of the insulation system according to the present invention is depicted in Figs. 4 — 8. In these figures there is also shown the structure of the insulation system according to the invention including securing brackets, joints, a possible insulating material for the spaces between the insulation panels (it is preferred that such an insulating material is a foamed insulating material such as polyurethane which is injected into the spaces under pressure). As shown there is with an insulation system according to the present invention, obtained an insulation comprising at least two layers of insulation plates that are joined together through the aid of a groove-and- ridge system.

The number of layers of insulating plates in such a system may also exceed two layers, and may even include three, four or five layers, although the minimum number of layers is two.

An advantageous and preferred insulating plate assembly adapted to be used in the insulating system and process according to the present invention, is depicted in Figure 9. Such a plate assembly is depicted as including three layers of insulating plates (EPS) that have been glued or welded together in a staggered configuration so as to produce a middle groove/bevel at one side of the plate assembly and a protruding ridge at the opposite side of the plate assembly. As also depicted in Figs 4 and 5, the middle layer of the assembly may even be displaced/staggered with respect to the two adjacent sides of the bottom and top plates in the assembly, creating a groove- and-ridge system around all four sides of the assembly plate structure with a protruding ridge at two adjacent sides of the plate assembly, and a groove at the remaining two adjacent sides of the plate assembly.

An mentioned supra, an insulating system according to the present invention will include at least two layers of insulating plates, and consequently an assembly of insulating plates may at a minimum include two layers of insulating plates. However, two layers of insulating plates located in a staggered configuration will provide an assembly structure wherein the plate assembly will provide a locked structure, but it will not provide a central groove and ridge system as explained supra with respect the three-layered structure. This will mean that adding a foam for providing a covering continuous insulation surface around the container will have as a consequence that the foam will expand freely over the top surface of the structure (unless a groove is provided by cutting in at least one of the plates of the assembly thereby increasing the production cost of the relevant plate). Consequently it is more preferred to use a three- layer assembly structure for the insulation system according to the invention as explained supra, although a two layer system is feasible, although not preferred.

As shown in Fig. 9, the three-layer plate assembly will also include a crack barrier of a type disclosed infra between at least two, and preferably all three, of the insulation plate layers of the plate assembly according to the invention.

When referring to a "glue" material and a "foaming insulation material" in the present disclosure, such materials may be different from each other, but will preferably include one and the same material. One example of such a material is foamed polyurethane which has good adhesive properties to EPS, thus making up a "glue", and it has also good insulating properties, thus making up a "foaming insulation material".

As shown in Fig. 5, depicting one embodiment of the insulation system according to the present invention, there are indicated "staggered glue joints" as well as "glasswool joint", indicating also other materials that may be used in the insulation system according to the present invention. In this embodiment glasswool (or even rockwool or other fibrous inert insulating material) may be blown between the plate joints and polyurethane may be injected into the joints/injection groove (see infra) as a glue material.

When laying the multi-layered (two or more) insulation thermal barrier according to the present invention, it will normally be started with laying the insulation plates (or insulation plate assembly) from the top of the cryogenic container (however, this is not strictly necessary since the laying of thermal insulation plates may commence at any location on the surface of the container). Plates/plate assemblies will at intervals be nailed/bolted to the container wall to ensure the necessary securing of the system. Such nails/bolts will in principle represent possible thermal bridges, but they are especially isolated through the second layer of insulation plates (or their location are determined and there are provided holes for them in the bottom layer of the plate assembly, whereby they are thermally insulated through the injection of a foaming insulating material (polyurethane) into the final insulation structure according to the invention). Also other forms for securing these plates are possible, e.g. through gluing the plates to the container wall.

The panels are now successively hooked in to each other through the aid of the groove- and-ridge system in the side edges of the plates/plate assemblies. One possible alternative groove-and-ridge system may be to equip the plates with a self-securing "click-system" like the one existing in floor panels or laminate plate for floors. As shown in Fig. 6 the connection area between the insulating plates is equipped with an expansion tunnel for the connecting/gluing and isolating material polyurethane which is injected into the joints after a section of the insulating plates have been laid. This insulating and expanding material will, by being injected under pressure, run out and seal all of the edge areas that are not tight between the insulating plates according to the invention.

After this first layer of isolation plates has been laid, secured and sealed, there will be laid on top of this layer a crack barrier in the form of a netting, a sheet or a cloth of a synthetic or natural material that may be or is impregnated with a polymer sealant that will harden on top of the first isolation layer and form a foundation for the second layer of isolation plates that is placed on top of the first layer in a similar manner. An example of a crack barrier may be a sheet or netting of polyethylene or polystyrene with a mesh size within the interval 0,01 to 100 mm² impregnated with polyurethane.

If the container/tank insulation according to the invention is made up of pre-made plate assemblies as explained supra, the forming of the layers including the crack barrier(s) and other structures for the tank insulation (e.g. securing spots in the form of take-outs for bolts/nails, groove(s) for insulating adhesive, etc.)) are included into the pre-made assemblies (see e.g. Fig. 9). The crack barrier is to prevent the insulation layers to split on account of the steep temperature gradient that the insulation system is to withstand.

In Figs. 7 and 8 there is shown a view of an embodiment of the structure of the insulation system according to the invention.

The method for laying the insulation plates/assemblies according to the invention is also shown in Figs. 10 - 18.

The production method for each of the individual insulation plates according to the invention is shown especially in Figure 16. Fig 18 may also be referred to concerning the stratification of the insulation assembly being shown in Fig. 8.

A special feature of the insulation plates of the present invention and being material in the improved sealing properties through the installation/assembly process of the total insulation structure according to the present invention, is the provision of expansion tunnels 61 for the polymeric substance (e.g. polyurethane) in the joining edges of the ridges/grooves on the groove-and-ridge assembly formation of the insulation plates (see fig. 6). Such tunnels 61 are provided in the insulation plates so as to form a continuous web to be filled with the expanding insulation/gluing material. Also, as shown in fig. 6, this feature of the groove-and-ridge assembly of the insulation plates according to the present invention will accommodate any curvature of the tank below in relation to flat or semi-flat plates being used for the insulation plates. Furthermore, a section of the ridge or groove part of the joint between plates is provided with an elevated edge 62 forming a sealing/fitting edge for the expansion tunnel 61. Since the insulation plates preferably are made of a soft or pliable material (e.g. foamed polyethylene or foamed polystyrene), the plates will accommodate some stress forces in the joint area of the expansion tunnel. This semi-elastic effect will ensure a mainly or completely tight expansion runnel area for the joint between the insulation plates. Also, on account of the curvature of the container surface below the insulation structure, the joining edges around the expansion tunnel will be pressed against each other further ensuring a tight junction of the edges forming the expansion tunnel.

On account of the semi-soft/pliable nature of the insulation material of the insulation plates, it will be possible to insert a probe/injection needle into the expansion tunnel at intervals around the container/crygenic tank or injection ports may be provided at special intervals of selected insulation plates to provide access to the expansion tunnel.

In an embodiment, after having assembled the insulation plates as explained supra, it will be possible to ensure a continuous insulating structure be injecting the expanding (polyurethane) foam into the expansion tunnels 61.

As also shown in figure 6, the vertical joining fissures between adjacent insulation plates, may be staggered with respect to each other, and consequently the expansion tunnels 61 are provided in both the horizontal and vertical joining edges of the insulation plates.

Infra follows different examples of insulation assemblies according to the invention. Their insulation properties are also indicated.

Examples:

INTRODUCTION

Tests have been carried out on an insulation panel for LNG tanks. The intention of the tests was to establish values for thermal conductance per unit of area for an insulation panel made of expanded, partially elastified polystyrene, and to expose the test panel to tensions which will occur in an actual case in an insulation system at these temperatures. The thermal conductance (hereafter called k_value) was measured at a warm side temperature of about 20 °C, and a cold side temperature of about -160°C, in horizontal and vertical positions. The was also measured after 5 subsequent temperature fluctuations, during which the temperature on the cold side of the test panel was varied between -162 °C and 10°C. These temperature variations will cause tensions inside the test panel as in an actual case.

TEST EQUIPMENT

The tests were carried out in a large scale guarded hot plate apparatus, with test section 2 by 3 m². The arrangement of the warm and cold plates is shown in Fig. 1.

The plywood frame inside the perimeter insulation is inserted into aluminium profiles in warm and cold plates to simulate the tensions in the test panel.

TEST INSULATION

The insulation specimen was made of slabs of expanded polystyrene with zones of flexible material, mounted on a 0.005 m aluminium sheet with stud bolts (Fig. 2).

The specimen was delivered from Ticon Isolering AS ready for mounting in apparatus. The size of the specimen was 2.0 by 3.0 by 0.265 m³.

INSTALLATION OF TEST PANEL IN APPARATUS

The convection free perimeter insulation of the test apparatus is built up of Styrofoam RM slabs and fiberglass cloth, bonded together with adhesive. The corner sections are made of 2-way flexible elastified Styrofoam.

The test specimen was inserted into the test section and sealed to the perimeter insulation with polyurethane glue forwarded from Ticon Isolering A/S.

The perimeter insulation was airtightly sealed and firmly bounded to the aluminum test plates of the apparatus by means of sealing compound. A cross section of the perimeter insulation is shown in. Fig. 3. INSTRUMENTATION

Temperatures were measured by means of copper-contantan thermocouples on the warm and cold plates and on the warm and cold surfaces of the insulation panel.

The temperature on the warm side of the insulation is measured on the aluminum foil vapor barrier, and temperature on the cold side on the aluminum sheet.

Additional thermocouples were mounted inside the insulation panel in 8 different zones and 4 different cross sections (Fig. 19).

All temperatures were recorded on a data acquisition system with 400 channels, transferred to a local computer for processing.

Power input to the tree sections of the main hot plate of the apparatus were measured by precision resistors and a precision voltmeter, and controlled by precision wattmeters.

CALCULATION OF THERMAL CONDUCTANCE

The evaluation of the heat leakage through the convection- free perimeter insulation has been made previously with the apparatus in horizontal convection-free position with the test cavity filled with rockwool with density 74 kg/m³. The thermal conductivity of this material was measured in a horizontal guarded hot plate apparatus. After installation of the test panel, the total heat flow was measured with the apparatus in horizontal and vertical positions. The apparent thermal conductance for the test panel in these two positions was calculated as follows:

k_value= Q _i / (F*T;) k_value= apparent thermal conductance per unit of area for the test panel (W/ m²K).

Q_i = heat flow through the test panel (W). F = area of test panel (m²).

T_i = temperature difference across the test panel (K)

Q_i=Q_t-Q_p Q_t = total heat flow (W).

Q_p=C_p*T_p Q_p = heat flow through perimeter insulation (W).

C_p = thermal conductance of perimeter insulation found by calibration test (W/K).

T_p = temperature difference across perimeter insulation (K).

The influence of convection is estimated by comparison of the apparent thermal conductance measured in horizontal and vertical positions.

The accuracy of the measurements is estimated to be better than ±71 % of the actual value.

TEST RESULTS

The thermal conductance was measured in horizontal, convection- free position after one cooling down, test no. 190, and vertical position, test no. 191. An increase of about 3 % was measured in the k_value compared with the value measured in horizontal position corrected to same mean temperature. This is well within the accuracy of the apparatus, and most of the difference is probably not due to convection in the test specimen.

The thermal conductance was also measured after 5 subsequent cooling downs in vertical and horizontal positions, test no. 192 and 193. No significant difference between these tests and tests no. 190 and 191 was found.

The test results are given in Table I. TABLE I:

Several thermocouples were placed inside the insulation panel in order to bridges or convection currents, see Table II, and Fig. 20, Fig. 21, Fig. 22 and Fig. 23. A survey of the measured temperatures are given in Fig. 20, Fig. 21, Fig. 22 and Fig. 23, on warm and cold side of the test panel.

INSPECTION OF TEST PANEL

The test panel was inspected visually from the warm side in horizontal position with the cold side at low temperature (-162º0). The test panel will then be partially exposed to the tensions caused by the low temperature at the cold plate, and it will be easy to observe cracks, damages, openings or channels inside the test panel.

Openings were made in the test panel to detect defects or cracks inside.

As expected, no damages, defects or faults in construction were found.

The test specimen with the cold side at -162 °C was removed from the apparatus and inspected from the cold side. The aluminum sheet at the cold side was removed to give a good overlook at the cold side of the insulation, No channels, defects or faults were detected. CONCLUSION

The small rise in apparent thermal conductance for the test panel construction from horizontal to vertical position, shows that there probably were none, or very small convection currents inside the test panel. The thorough examination after the test shows good workmanship during the panel mounting, and no cracks or damages inside the panel.

The test panel construction had a reasonable value for the apparent thermal conductance at the measured temperatures, and seems to withstand in a good manner the exposed tensions during this test.

Table II:

Area: See Fig. 20-23.

INTRODUCTION

Testing of Sunpor SE (rigid and flexible polystyrene) have been carried out at three temperature levels, 20 °C, -70 °C and -153 °C. Totally 8 different tests are executed, but not all the tests for both materials at the three temperature levels.

No standards are made for testing at low temperatures. As a basis for the testing the actual standards (ISO or ASTM) is used.

For each test, modifications done to the actual standard, are described.

The low temperature tests are carried out in a cold box, cooled by a Philips cryogenerator. The temperature is measured by mean of thermocouple in the air stream- A sketch of the cold box is shown in Fig. 24.

In some of the tests, values of elongation etc. should have been recorded during testing of the specimens. This is quite difficult when the test specimens are placed in the cold box. These types of tests are recorded on a video tape, which means that the values have been read at a later time, with a good accuracy.

TEST PROGRAMME

A survey of the test programme showing tests carried out on each material and temperature level, is shown in Table 2.1 for rigid material and in Table 2.2 for flexible material. The number of test specimens is decided by the client.

Table 2.1: Test programme for rigid material

Table 2.2: Test programme for flexible material, each direction

DESCRIPTION OF TEST METHODS

Test no. 1/2: Compression test/E-modulus

The test is described in ISO 844 - 1978: "Compression test for rigid materials". The test method used is as follows:

The test specimen is glued between two pieces of plywood. The lower part is fastened to the test frame. To the upper plywood plate a triangular plywood plate is fastened with moveable metal bars. This triangular plate is connected to lines, which are running over two wheels. Stressing the lines by filling a tank with water, compresses the material. The displacement as a function of force is registered by means of a dial indicator compressive test.

The test specimen used had the following dimensions: 55 • 55 • 40 mm³. Totally 4 test specimens are tested at each temperature level.

Compressive strength σ₁₀ (kPa) is given by the formula:

where

F_ra is the maximum force reached (in Newtons)

s_o is the initial area (mm²) of the cross-section of the test specimen

Compressive stress σ₁₀ (kPa) at 10% relative deformation is defined as:

where

F₁₀ is the force (N) corresponding to a relative deformation of 10 %

s_o is the initial area (mm²) of the cross section of the specimen

Test no. 3/4: Maximum tensile stress/E -modulus

The test is described in ISO 1926: "Standard test method for Cellular plastics Determination of tensile properties of rigid materials". The standard prescribes testing of totally 5 pieces. The test pieces used had the following shape and dimensions:

The test pieces were somewhat smaller than prescribed in the standard. This is done to make it possible to carry out the tests in the cold box.

The test specimens were glued to two pieces of plywood, using standard epoxy adhesive. The lower part is fastened to the bottom of the test frame. At the upper part a line running over two wheels are fastened. A tank is fastened to the other end of the line. Filling the tank with water means stressing the material. The elongation corresponding to a given force is recorded at intervals of 5 kg.

The rate of filling the water is adjusted to obtain rupture during 3-6 min.

Maximum tensile stress σ_m expressed in kilopascales is given by the formula:

where:

F_m - is the maximum force (N) applied to the test piece during the test

1 - is the original width (mm) of the parallel length of the narrow section of the test piece h - is the original thickness (mm) of the parallel length of the narrow section of the test piece

E-modulus is defined as the angle of inclination of the curve of elongation as a function of the force.

where: δ - tensile stress (N/mm^z)

Δl - elongation of material at δ.

I_o - length of test specimen Test no. 5: Shear modulus

The test method is described in standard ISO 1922-1981 : "Cellular plastics - determination of shear strength of rigid materials".

4 specimens are tested at each temperature level. The standard prescribes 5 specimens.

The standard prescribes test specimens with the following dimensions (length - width - thickness): 254 mm · 50 mm · 25 mm.

To make it possible to do testing in the cold box, smaller test specimens were used in these tests. The following dimensions (length - width - thickness) were used

100 mm · 40 mm · 25 mm.

At the beginning some larger test specimens were tested, but due to very strong material, the size were reduced, to reduce the force needed to obtain rapture. The test equipment could not bear the weight needed to rupture the test specimen used initially.

The test specimens were glued to two pieces of plywood, with epoxy adhesive. One of the plywood pieces was fastened to the test frame, the other part is moveable. At the moveable part a line running over two wheels with a tank in the other end are fastened. Filling this tank with water stresses the material and moves the moveable plywood piece and the test specimen upwards.

At the moveable plywood piece lines are drawn with intervals of approximately cm. A ruler is fastened at the bottom of the test frame. The ruler are not moved during the testing. This system makes it possible to recognize elongation of the material.

The tank is filled up with water until rupture is obtained. The tests are recorded at a video tape, and the elongation is read afterwards.

The test equipment is shown in figure 27.

Test no. 6: Thermal expansion

The test is described in ISO 4897 - 1985; "Cellular plastics - Determination of the coefficient of linear thermal expansion of rigid materials at sub-ambient temperatures". The standard prescribes testing of totally 5 specimens with the following dimensions:

Length: 900 ÷ 0-20 mm

Width: 100 to 300 mm

Thickness: 25 to 50 mm

The material used in this test had the following dimensions:

Length: 244.5 mm

Width: 43.5 mm

Thickness: 42.0 mm

Totally 4 specimens of each material are tested.

The test specimens are glued between two pieces of plywood. The lower part is fastened to the test frame. At the center of the upper plywood plate a stainless steel rod is fastened. The rod is connected to a dial indicator placed outside the cold box. The compression/expansion of the material is recorded at different temperatures during cool- down or heating of the material.

Calculation of mean coefficient of linear expansion (-63°C to 20°C):

where:

α - is the mean coefficient of linear expansion, in reciprocal degree kelvins;

T_i - is the higher temperature selected, in degree kelvins;

ΔL - is the change in length, in millimeteres, of the test specimen between temperatures

T_i and T₂ L₀ - is the original length, in millimetres, of the test specimen at 23 ± 2 °C.

Test no. 7: Thermal conductivity

The test is executed in accordance with ASTM standard C 177 - 85: "Standard test method for Steady - State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot - Plate Apparatus". Test no. 8: Poissons ratio

No standard describes this test. The Poissons ratio μ is defined as the ratio between elongation and contraction of the material during tensile stressing:

where

Δb - is the change in width (mm). b_o - is the original width (mm) Δl - is the change in length (mm) l_o - is the original length (mm)

The test specimens have the same shape and dimensions as used in test no. 3 and 4, and the tests are carried out in the same way.

TEST RESULTS

The mean value (x) and standard deviation (s) is given in the table for each test.

Rigid material

Test no. 1/2 Compression test / E-modulus.

Table 4.1: Test result compression test /E-modulus for rigid material. Density p = 23.2 kg/m³

4 specimens were tested at —70 °C. One of them was pressed out of the equipment. *) Did not reached 10% compression, the calculated strength is maximum compressive stress (x)= The mean value, (s)= The standard deviation

The test results are shown in Fig. 28 and Fig. 29

Test no. 3/4 Maximum tensile stress 1 E - modulus

Table 4.2: Test result tensile stress /E-modulus 'for rigid material. Density ρ = 22.8 kg/m³

8 specimens were tested at 163 °C and 4 at - 70 °C.

2 tests were not possible to read from

(x)= The mean value. (s)= The standard deviation

The test results are shown in Fig. 30 and Fig. 31

Test no. 5 Shear modulus

Table 4.3: Shear modulus rigid material. Density ρ = 23.2 kg/m³

8 specimens were tested at each temperature level. At - 163 °C one test was not readable on the videotape. For the 8th specimen at 20 °C the rupture came in the glue and not in the test specimen. (x)= The mean value, (s)= The standard deviation

The test results are shown in Fig. 32 and Fig. 33

Test no. 6 Thermal expansion

Table 4.4: Thermal expansion, rigid maternal. Density ρ = 23.2 kg/m³

(x)=The mean value, (s)= The standard deviation.

The test results are shown in Fig. 34 Test no. 7 Thermal conductivity

Table 4.5: Thermal conductivity of rigid material. Density 25.0 kg/m³

The test results are shown in Fig. 35

Test no. 8 Poissons ratio

Table 4.6: Poissons ratio for rigid material. Density ρ = 22.8 kg/m

4 specimens were tested at - 163 °C. One of them was not readable on the video tape. (x)= The- mean value, (s)= The standard deviation Flexible material

Test no. 1/2 Compression test/E-modulus

Table 4,7: Compressive stress/E-modulus for flexible material 1/161-4. Density ρ= 24:5 kg/m³ Test direction: ||

^*)Did not go 10 %. The calculated strength is maximum compressive strength.

4 specimens were tested at each temperature level, but at each temperature level one specimen was pressed out of the equipment.

(x)= The mean value, (s)= The standard deviation

The test results are shown in Fig. 36 and Fig. 37.

Table 4.8: Compressive stress/E-moduIus for flexible material 1/161-5. Density ρ w 20.8 kg/m³ Test direction

4 specimens were tested at -70 °C, but one was pressed out of the equipment. (x)= The mean value, (s)= The standard deviation

The test results are shown in Fig. 38 and Fig. 39.

Test no. 314 Maximum tensile stress / E - modulus

Table 4.9: Test results maximum tensile stress/E-modulus for flexible material 1/151-4. Density ρ = 22.0 kg/m³ Test direction: )|

4 specimens were tested at -70 °C. One of them was not readable on the video tape. (x)= The mean value, (s}= The standard deviation

The test results are shown in Fig.40 and Fig. 41.

Table 4.10: Test results maximum tensile stress/ E-moduIus for flexible material 1/161-5. Density 20.8 kg/m³ Test direction:

8 specimens were tested at -163 ºC. One of them was not readable on the video tape. (x)= The, mean value, (s)W The standard deviation

The test results are shown in Fig. 42 and Fig. 43

Test no. 5 Shear modulus

Table 4.11: Test results shear modulus for flexible material 1/161 - 4 Density ρ = 22.0 kg/m³ Test direction: ||

(x) = The mean value, (s) = The standard deviation

The test results are shown in Fig. 44 and Fig. 45

Table 4.12: Test results shear modulus for flexible material 1/161-5. Density ρ = 20.0 kg/m³ Test direction:

8 specimens were tested at -163 °C. One of them was not readable on the video tape. (x)= The mean value, (s)= The standard deviation

The test results are shown in Fig. 46 and Fig. 47

Test no. 6 Thermal expansion

Table 4.13: Test results thermal expansion for flexible material 1/161-4 Density ρ = 22.0 kg/m³ Test direction: ∥

The test results are shown in Fig. 48 Table 4.14: Test results thermal expansion for flexible material 1/1161-5 Density ρ = 20.0 kg/m³. Test direction:

Specimen no. 3 and 4 were tested with start temperature -163 °C. The temperature rose to -60 °C. Then hot air was blown into the cold box. Because of this supply of air the steel rod jumped off the specimen and the test had to be stopped. The test results are shown in Fig. 49.

Test no. 7 Thermal conductivity

Table 4.2.5: Thermal conductivity of flexible material 1/161-4. Density 24.4 kg/m³ Test direction: ||

The test results are shown in Fig. 35

Table 4.16: Thermal conductivity of flexible material 1/161-5. Density 27.9 kg/m³ Test direction:

The test results are shown in Fig. 35

Test no. 8 Poissons ratio

Table 4.17: Poissons ratio for flexible material 1/161-4 Density 24.4 kg/m³ Test direction: ||

4 specimens were tested at 20°C. One of them was not glued well enough, so rupture occurred in the glue and not in the test specimen. (x)= The mean value, (s)= The standard deviation

Table 4.18: Poissons ratio for flexible material 1/161-5. Density p = 20.0 kg/m³ Test direction:

(x)= The mean value, (s)= The standard deviation

CONCLUSION

A total of 8 different tests are executed at three temperature levels (-163°C, -70°C and 20°C} for rigid expanded polystyrene and flexible expanded polystyrene in 2 directions.

The actual standards describing the tests are modified, to make it possible to execute the tests in a cold box.

As shown on the curves for the different tests, the variation -in the test results is significant. Especially for the frigid material, elongation and contraction of the material was minimal, and exact values were difficult to record.

INTRODUCTION

Tests have been carried out on an insulation panel for LNG tanks.

The intention of the tests was to establish values for thermal conductance per unit of area for an insulation panel made of slabs of expanded polyurethane with strips of elastified material (cold side) and polyurethane (warm side) between, and to expose the test panel to tensions which will occur in an actual case in an insulation system at these temperatures. The thermal conductance (hereafter called k_value was measured at a panel warm side temperature of about 20 °C, and a cold side temperature of about -162°C, in horizontal and vertical positions. The k_value was also measured after 5 subsequent temperature fluctuations, during which the temperature on the cold side of the test panel was varied between -162 °C and 10 °C, with stabilizing periods of 4 hours in warm and cold end. These temperature variations will cause tensions inside the test panel as in an actual case.

TEST EQUIPMENT

The tests were carried out in a large scale guarded hot plate apparatus, with test section 2 by 3 m², specially build for such tests.

The arrangement of the warm and cold plates is shown in Fig. 1.

The plywood frame inside the perimeter insulation is inserted into aluminium profiles in warm and cold plates to obtain the tensions in the test panel as in a real installation.

TEST INSULATION

The insulation specimen was made of slabs of expanded polyurethane with strips of flexible material on the cold side and strips of polyurethane on warm side between the slabs, mounted on an 0.005 m aluminium sheet with stud bolts, Fig. 2. The specimen was delivered from UNITOR ASA, Marine Contracting ready for mounting in the apparatus .

The size of the specimen was about 2.0 by 3.0 by 0.29 m³.

INSTALLATION OF THE TEST PANEL IN APPARATUS

The convection free perimeter insulation of the test apparatus is built up of Styrofoarn RM slabs and fiberglas cloth, bonded together with adhesive. The corner sections are made of 2-way flexible elastified Styrofoam.

The test specimen was inserted into the test section and sealed to the perimeter insulation with polyurethane adhesive forwarded from UNITOR ASA, Marine Contracting. The perimeter insulation was airtightly sealed and firmly bounded to the aluminum test plates of the apparatus by means of sealing compound.

A cross section of the perimeter insulation and some of the insulation panel is shown in Fig. 50.

INSTRUMENTATION

Temperatures were measured by means of copper-constantan thermocouples on the warm and cold plates and on the warm and cold surfaces of the insulation panel. The thermocouple wire is calibrated at an accuracy better than ±0.3 °C traceable to the international temperature standard (ITS-90), for the temperature range used in the tests.

The temperature on the warm side of the insulation is measured on the aluminum foil vapor barrier, and temperature on the cold side on the aluminium sheet.

Aditional thermocouples were mounted inside the insulation panel in 10 different zones and 3 different cross sections Fig. 51 (warm side, middel zone and cold side).

All temperatures were recorded as a voltage on a data acquesition system with 400 channels, transferred to a local computer for processing.

Power inputs to the three sections of the main hot plate of the apparatus were measured by precision resistors and a calibrated precision digital voltmeter, and controlled by calibrated precision wattmeters.

CALCULATION OF THERMAL CONDUCTANCE

The evaluation of the heat leakage through the convection- free perimeter insulation with part of a polyurethane adhesive joint has been made previously with the apparatus in horizontal convection-free position with the test cavity filled with rockwool with density 70 kg/m³. The thermal conductivity of this material was measured in a horizontal guarded hot plate apparatus. After installation of the test panel, the total heat flow was measured with the apparatus in horizontal and vertical positions. The apparent thermal conductance for the test panel in these two positions was calculated as follows: k_value= Q _i / (F*T_i;) k_value= apparent thermal conductance per unit of area for the test panel (W/ m²K).

Qi = heat flow through the test panel (W). F = area of test panel (m²). .

Ti = temperature difference across the test panel (K)

Q_i=Q_t-Q_p Q_t = total heat flow (W).

Q_p=C_p*T_p Qp = heat flow through perimeter insulation (W).

T_p = temperature difference across perimeter insulation (K).

The accuracy of the measurements is estimated according to methods described in NIST Technical Note 1297 of 1993 (NIST = National Institute of Standards and Technology Gaithersburg, USA) as good as possible in such a complicated construction, to be better than ±7% of the actual value.

TEST RESULTS

The thermal conductance was measured in horizontal, convection-free position after one cooling down, test no. 198, and in vertical position, test no. 199.

The thermal conductance was also measured after 5 subsequent temperature cycles in vertical and horizontal positions, test no. 200 and 201.

A rise of about 5.5 % was measured in the k_value between horizontal tests no 198 (first H) and vertical test no. 199 (first V).

A rise of about 9.5 % was measured in the k_value between horizontal test no 198 (first H) and vertical test no 200 (second V).

Between horizontal tests no 198 (first H) and no 201 (second H) no significant difference were measured. These differences are small margins compared to the accuracy of the measuring method

The rise in the k value in the vertical position compared to the value in horizontal position is probably due to cracks observed in the test panel edges described in chapter 8: Inspection of the test panel. It could also explain the rise in the k value between vertical test no. 199 (first V) and vertical test no 200 (second V) due to development of the cracks during the temperature cycles.

These cracks were only observed in the edges near by the adhesive joint, and will probably not occur in a real insulation panel.

The test results are given in Table 7.1.

TABLE 7.1:

Several thermocouples were placed inside the insulation panel in order to give information about heat bridges or convection currents, see Table 9.1 , and Fig. 52, Fig. 53, Fig. 54 and Fig 55 (unfortunately some of the thermocouples were broken during the test).

A survey of the measured temperatures is given in Fig. 52, Fig. 53, Fig. 54 and Fig. 55, on warm and cold side of the test panel. INSPECTION OF TEST PANEL

Inspection from warm side of test panel

The test panel was inspected visually from the warm side in horizontal position with the cold side at low temperature (-162°C). The test panel will then be partially exposed to the tensions caused by the low temperature at the cold plate, and it will be easy to observe cracks, damages, openings or channels inside the test panel.

The warm side was carefully inspected to see if there were any dents or channels underneath the aluminium vapour barrier, or underneath the sealing compound (ERFO GUARD FP-VB) upon the polyurethane joints between the polyurethane slabs (see Fig. 50).

The sealing compound (ERFO GUARD FP-VB) in use between the polyurethane slabs, were inpected very carefully to observe if there were any damages or channels, especially around the dents in the aluminium vapour barrier.

No such damages, cracks or channels were found at all, and the adhesion to the aluminium foil and the insulation seemed to be of a very good shape. The sealing compound had withstand the test in a good manner.

Inspection from inside the test panel

Openings were made in the test panel edges to detect defects or cracks inside.

The dents in the aluminium vapour barrier and the sealing compound (ERFO GUARD FP-VB) were carefully excamined from the inside, espesially for poor adhesion.

No damages or channels were found underneath, so the observed dents on the aluminium foil surface are probably caused by a small compression on the warm side and could have had no effect on the measured values.

The adhesion of the aluminium foil and the sealing compound to the insulation underneath was considered as very good, Some small cracks were found in the test panel (2.0 by 3.0 m) edge area near the limit between the test apparatus perimeter insulation and the test panel as shown on Fig. 56. These cracks were mostly situated in the middle of the polyurethane slabs near to the joints between the slabs. The cracks do not seem, in any places, to reach from the cold to the warm side.

A more close examination showed that the cracks seemed to start in the limit between the test panel edge and the perimeter insulation (adhesive joint) probably due to a less flexible zone in this edge area.

The centre part of the test panel which most realistically simulates the actual service condition in temperature distribution, stress and deformation for the overall panel design, showed no sign of such cracks, and no other failures were observed.

Based on this and the inspection of the pieces cut out from the test panel after the test run, it can be concluded that the cracks probably must have been caused by unwanted higher tension near to the limits at the adhesive joint used to install the test panel in the test apparatus. Further, the cracks were small and were not in any way connected to each other, but this could explain the small rise in the measured heat conductance.

Inspection from cold side of the test panel

The test panel and the perimeter insulation with the cold side at -162 °C was then removed from the apparatus aid inspected from the cold side in cold conditions.

The aluminium sheet at the cold side was-removed to give a good overview at the cold side of the insulationsystem.

No channels, defects or faults except the cracks in the edge area mentioned above, were detected.

Some of the stud bolts were cut out from the panel and inspected carefully. There seem to be no damages or defects on the inspected stud bolts.

CONCLUSION

The small increase in apparent thermal conductance for the test panel from horizontal to vertical position, shows that there probably must have been very small convection currents inside the test panel, and it is probably caused by the observed cracks mentioned in chapter 8.

Examination of the temperatures inside the test panel showed on Fig. 51 and 52 to 55 and in Table 9.1, showed that it seems to have been small convection currents in the flexible material on cold side of the vertical joints between the polystyrene- slabs (for instance between panel no. II and no. VI on Fig. 57), but this seems to have had very small effect on the measured value for thermal conductance.

The carefully examination after the test shows good workmanship during the panel mounting, and no damages or defects inside the panel, just the small cracks (not caused by the panel construction) mentioned above were found.

The test panel construction had a reasonable value for the apparent thermal conductance at the measured temperatures, and it seems to withstand in a good manner the exposed tensions during this test. And there would probably not have been found any cracks or defects if it had been possible to control tension in the edge area.

Table 9.1

TC No., Area, Depth, and Panel No.: See Fig 57, 51 and Figs 52-55.

Claims

C l a i m s

1. Insulation structure for cryogenic tanks or containers comprising plates of an insulating material, said plates being equipped in their side edges with mutual cooperating securing structures for through their assembly to create a mainly continuous layer of the insulating material, the securing areas in the insulation plates additionally comprising at least one groove for the addition of a polymerizing insulation material under pressure for filling optional cracks or fissures and/or openings between each insulation plate in the assembly.

2. Insulation structure according to claim 1, wherein the insulation plates are made of expanded or extruded polystyrene (EPS).

3. Insulation structure according to claim 1 or 2, wherein the polymerizing insulation material is a liquid material being injected into the relevant groove in the insulation panels.

4. Insulation structure according to claim 3, wherein the insulation liquid is polyurethane.

5. Insulation structure according to any of the claims 1 - 4, wherein the cryogenic tank/container adapted to transport cooled liquids within the temperature interval —50 to -273°C, preferably -100 to -250°C, more preferred -125 to -200°C.

6. Insulation panel assembly comprising at least two insulation panels laid on top of each other and including in the contact surface between the plates a crack barrier in the form of a netting, sheet or cloth of a synthetic of natural material, and displaying a groove in at least one of the edges of the panel assembly for the provision of a liquid foaming insulation material to the panel assembly.

7. Insulation panel assembly according to claim 6, wherein the number of insulation panels is three, and wherein at least one of the layers of the assembly is displaced with respect to the positioning of the panels of the other layers.

8. Insulation panel assembly according to claim 7, wherein the middle layer of the assembly is displaced with respect to the top and bottom layer for creating a ridge-and- groove structure in at least two of the side edges of the assembly.

9. Insulation panel assembly according to claim 8, wherein the middle layer is displaced with respect to the top and bottom layer for creating a ridge-and-groove structure in all of the four side edges of the assembly.

10. The use of an insulation panel assembly according to any of the claims 6 - 9 for thermally insulating spherical cryogenic containers/tanks.

11. Process for adding in insulation structure according to any of the claims 1 - 9, wherein it onto the surface of the cryogenic tank is added a layer of e foundation material (SCRIM), onto which material there is added a first insulating layer comprising an adhesive material and to said adhesive material there is added at least one of an insulation panel or an insulation panel assembly according to any of the claims 6 - 9, whereupon it to the relevant injection groove in the insulation panels or insulation panel assemblies is added a foaming and liquid insulation material under pressure, said liquid insulation material being capable of hardening in the relevant injection groove for the creation of a continuous insulation layer, and where, in the event of an insulation panel assembly is not used, the insulation layer is added a crack barrier, and onto which crack barrier a second layer of insulation panels corresponding mainly to the first layer, and the layer- forming process optionally being repeated any number of times, and onto said insulation structure there optionally is added a foil of a radiation-reflecting material.

12. Process according to claim 11 , wherein the insulation panels comprise panels of expanded or extruded polystyrene.

13. Process according to claim 11 or 12, wherein the insulating, liquid, foaming material being added to the injection grooves comprises polyurethane.

14. Process according to any of the claims 11 - 13, wherein some or all of the insulation panels in the first insulation layer or insulation panel assemblies are nailed/bolted to the container/tank wall.