DK151913B - PROCEDURE FOR PREPARING A FOAMED PLASTIC INSULATION COVER ON A TUBE - Google Patents

Description

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DK 151913B

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method of producing a foamed plastic insulation coating on a tube, in particular a metal tube such as a steel tube, by applying liquid, foamable plastic layers having different density distribution over

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overall thickness of the plastic layers, optionally affixing one or more additional materials to form one or more additional inner layers, and optionally applying the corrosion-resistant coating first.

It has hitherto been proposed to insulate tubes by spraying one or more layers of foamed plastic insulation, such as polyurethane, followed by curing and coating or wrapping the insulating layer with a protective layer or barrier layer as described e.g. in U.S. Patent No. 3,480,493. The layer of foam insulation resulting from such a process usually has an apparent density of average size such that it has properties that are a compromise between those required to achieve maximum heat insulation properties and those required to achieve maximum strength, compressive strength, and acid resistance.

U.S. Patent No. 3,644,168 describes a molded structural material made in a one-step process by introducing a foam material into a mold. The confining effect of the mold causes the development of a high density layer where the foam material contacts the mold. The application of the teachings of this patent to the problem of pipe coating would require enclosing the tube in a confining form to provide a space in which the foam material could be confined during foaming. In the present invention, no mold or confinement is used, but instead the foamable polyurethane plastic mats are all simply sprayed onto the tube, and are cured without confinement, depending on the formulation of the foamable plastic material and the amount of foaming agent to obtain the desired density in each layer.

In U.S. Patent No. 3,782,998, the two-layer foam coating on the steel building is arranged with the high density layer closest

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2 by the steel and the low density layer is exposed to the atmosphere. The arrangement is an essential feature of said patent, as set out in column 2, lines 23 to 60, to enable 5 to perform the process on the interior surface of a steel building when the outside temperature is low. The foam layer! low density will not develop enough heat to self-cure when applied directly to the metal under such j

conditions according to said patent specification and do not hang without I

in trouble fixed to the metal. j i

In the process of the invention, the low density foam layer is placed closest to the tube and the high density foam layer is | the outside side. The opposite of that of U.S. Pat.

3,782,998 stated. This sequence of layers in the finished coated tube not only provides better protection against the physical abuse to which the coated tube is subjected, but the high density exterior layer further acts as a vapor barrier for the low density inner foam layer. thereby delaying the diffusion of the trichloromonofluoromethane propellant blocked within the cells of the low density internal foam. The diffusion of the f 1 urcarbon fuel from the foam cells results in a decrease in heat insulating properties, as well as pollution of the environment. The higher solids content of the high density outer foam layer delays diffusion of the propellant to a greater extent than the low density inner layer. In the arrangement of the low-density exposed U.S. Patent No. 3,782,998, the fluorocarbon propellant can freely diffuse into the atmosphere at a higher rate, leading to a relatively rapid decline in heat insulating properties.

In addition, the high-density hard outer foam layer not only protects the inner layer from abrasion, but due to hardness and stiffness, it protects the inner layer from being crushed by force of its annular strength; this feature allows the coated tube manufactured in accordance with the present invention to maintain its high heat insulating capacity at greater depths in either soil or water than a low density foam insulation tube can.

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3 U.S. Patent No. 3,802,948 is similar to U.S. Patent No. 3,644,168 in that it requires a plywood mold. In addition, the density of the inner layer of foam is generally higher than the density of the relatively thick outer layer of foam, at this point corresponding to U.S. Patent No. 3,644,168 and different from the present invention.

U.S. Patent No. 3,657,036 discloses a combination of a low density plastic layer with a surface of a higher density plastic material. This structure is chosen to achieve a low weight panel in combination with a sufficient surface strength. This known invention has no relation to the present invention, the object of which is to provide a tube in sunbaths which at one time in soles and possesses favorable surface properties.

It has also been proposed in U.S. Patent No. 4,094,715 to spray pipes with a foam-forming, liquid material, then provide the forming foam with a film-like protective layer before being completely cured, thereby exerting a pressure which only increases. the density of the foam near the outer surface thereof. The major disadvantage of the method is that it is confined to a spirally wound, protective surface layer which is applied under tension to obtain a ten liter visible increase in the density of the outermost layer of the foam. Such an approach can be difficult to control in commercial operations, viz. is set to the desired density, since the extent of the increase in apparent density and the thickness of the high density layer depends on several different critical factors including the temperature of the foaming plastic, the speed of the foaming material, the speed of the foaming plastic, the time , which extends prior to application of the protective layer, and the voltage applied to the protective layer during application. All of these factors influence the extent of curing of the foamed plastic prior to application of the protective layer. In addition, the thickness of the layer of increased density depends on the thickness and compressibility of the mass of low density foam already present.

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The object of the invention is therefore to avoid the aforementioned disadvantages of the prior art and to provide a method which is simple and inexpensive to perform, is not very sensitive to variations in the embodiment and which provides a product with an excellent combination of thermal insulation ability , strength, and acid resistance.

Thus, the present invention provides a method for producing a foamed plastic insulation coating on a tube, particularly a metal tube such as a steel tube, by applying liquid, foamable plastic layers of different density distribution over the total thickness of the plastic layers, optionally affixing it to the tube. or more additional materials to form one or more additional internal layers, and optionally, the tube is first further applied to a corrosion-protective coating, the method being characterized in that at least one inner plastic layer and an outer plastic layer are applied one after the other on the pipe respectively. the additional inner layer (s) and any anti-corrosion coating and foamed to various densities where the thickness and density of the outer layer are allowed to adjust independently without external restriction, where the inner layer is allowed to have a density of 0.024 ° C. 0.096 g / cm 3 and the outer layer t is estimated to have a density of at least 25% greater than the density of the inner layer, and where the thickness of the outer layer is allowed to constitute 5-30% of the total thickness of the two plastics.

As a foamable plastic mass, a polyurethane mass can advantageously be used here. However, the use of this process is not limited to polyurethane masses and all foamable plastic masses can be used in this process.

35 Since the thickness and density of each layer are independent of the other, it can be set and controlled separately. The method according to the invention makes it possible to use an inner layer of high insulation value and low cost together with an outer layer

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5 of higher strength and higher density and therefore a layer at a higher price. The two layers together provide a combination of properties that are optimal for pipe insulation and protection, at the 5 lowest possible total cost.

The magnitude of the density difference between the inner and outer insulating layers to obtain optimal results varies, among other things, depending on the pipe diameter, the ratio of the layer thicknesses, the minimum strength desired, and the temperature difference between the pipe and the surroundings. If desired, the inner layer may be divided into two or more layers applied one after the other and with different physical properties.

In the drawing, FIG. 1 is a cross-sectional view of one embodiment of the invention; and FIG. 2 is a cross-section of an alternative embodiment.

In FIG. 1, a metal rudder 10 is provided with an inner layer 12 20 of low density (0.032-0.096 g / cm 3) of e.g. rigid polyurethane foam fabric having a thickness of about 2.54 cm to 15.24 cm and a second layer 14 of rigid polyurethane foam soldering having a density at least 25¾ above the density of layer 12 and having a thickness of 5-30¾ of the total thickness of layers 12 and 25 14.

In a preferred embodiment of the invention, the inner layer of foam material in the sole 1 is not only different from the outer layer (s) in that it has a lower ten-layer visual charge density and thus a higher thermal insulation capacity, but it differs. say also by having a higher heat resistance, ie. that it is stable at a higher temperature until approx. 180 ° C than the outer layer (s) of foam insulation, which need only be stable up to a temperature of approx. At 90 ° C.

Another embodiment is shown in FIG. 2, wherein pipe 10, designed for hot liquids at a temperature of about 150 ° C to approx.

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6 180 ° C, is provided with an internal insulating layer divided into a first insulating part or a first insulating layer 20 of e.g. Low density foamed polyurethane made to have stability at a temperature up to approx. 180 ° C, and a second insulating portion or insulating layer 22 of approximately the same polyurethane foam material having approx. the same low density but made to be stable only at temperatures up to approx. 90eC. The outer layer 24 of e.g. High density polyurethane foam has a density which is at least 25% above the density of each of the layers 20 or 22 and has a thickness of 5-30% of the total thickness of the layers 20, 22 and 24.

By another perform! see form in which tubes 20 are intended for transporting cryogenic liquids at very low temperatures of 15 -130 ° C, layers 20 are made to be semi-rigid instead of rigid to avoid brittleness and possible cracking during use, while layers 22 and 24 are, however, made to have usual stiffness.

In the practice of the method of the invention, the tube, usually made of steel, is first heated to remove condensed moisture and purified to remove impurities, flakes and rust. Any conventional method of cleaning can be used such as sandblasting, brushing or the like.

If desired, two or more of such methods may be used in combination.

In some cases, it may be desirable to provide the pipe surface with a corrosion protection layer prior to application of the foaming 3Q plastic, although this is not absolutely necessary. Any usual anti-corrosion layer may be used, such as wrapped polyethylene / butyl adhesive tape, epoxy coating, heat activated adhesive or asphalt. The foamable thermoplastic material can be applied directly to the bare tube or to the surface of any corrosion protection coating previously provided with the tube. It is usually desirable that the tube temperature be raised to above room temperature, the temperature selected being dependent on the nature and composition of the

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7 The plastic material to be foamed. The latter is usually applied by spraying by means of a spray nozzle by rotating and passing the tube past various nozzles. A wide variety of compositions can be used for the foamable liquid polyurethane plastic material, and the choice depends on which properties are just desired by the final product. A particularly desirable composition is a liquid mixture of constituents which can react to form a polyurethane and containing a conventional foaming agent in an amount sufficient to form a foam having the desired apparent density, which may be from 0.024 to 0.096 g / cm 3. The first layer of foamable liquid is allowed to raise by the action of the foaming agent. The thickness of the first µg foam layer may vary over wide limits depending on the same factors mentioned above in connection with differences in the density of the insulating layers, such as the tube diameter and the temperature at which the tube with content is to be used, and may be used. generally vary from approx. 2.54 to 15.24 cm.

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The second or outer layer 14 or 24 of foamy liquid plastic material is then applied to the first foamed insulating layer by spraying in the usual manner on the surface of the tube as it rotates and moves forward.

The second layer can be applied to the first before or after the curing of the first layer, and even before the foaming of the first layer is completed. It is preferably applied prior to curing of the first layer. In one advantageous embodiment, the composition of the second foamable plastic material differs from the first solely in the amount of foaming agent used and is set to provide a foamed plastic insulation layer having an apparent density at least 25% higher than the apparent density of the first layer, and with a thickness of 5-30% of the total thickness of the two layers. In another advantageous embodiment, the outer layer 14 or 24 may have a lower heat resistance than the inner layer or greater stiffness or both.

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The total thickness of the foam in the sun is present as well as the thickness of the inner layer (about 2.54-15.24 cm) can vary, among other things. depending on the temperature difference between the tube content and the ambient of the tube, the tube diameter and the apparent density of the foam.

At a temperature difference of 41.5 ° C to 1500 ° C, a thickness of approx. 2.54 cm to 15.24 cm. The greater the temperature difference between the pipeline and the surroundings, the thicker the insulation should normally be. Cryogenic industries use e.g. usually polyurethane foam fabric layers 7.6 to 15.24 cm thick due to large temperature differences. For hot oil pipes, the difference is usually from 55.50 C to 89 C. For hot oil pipelines, the thickness usually ranges from 2.54 cm to 6.4 cm. If a tube for molten sulfur is used, it will normally be provided with a foam insulation of 6.3 to 7.65 cm in thickness, the inner layer 12 or 20 being made as a layer of high heat resistance, ie. a layer which is stable at 20 temperatures up to 149 ° C. A hot oil pipe, when buried in the soil, will normally require a foam sponge of 5.1 cm or less. Polyurethane foam has an exceptionally low K factor of the order of approx. 6.94 x 10-6 g cal / cm 2 / sec / ° C / cm as opposed to a K factor of approx. 0.39 for glass foam. In the case of a polyurethane foam having an apparent density of 0.048 g / cm 2, a 5.1 cm thick layer results on a 15.24 cm diameter tube used at a temperature difference of 69.4 ° 0. , in a heat loss (or increase) of approx. 43.7 x 10 ~ 6 g cal / sec / cm 2.

30 A suitable recipe for preparing a satisfactory rigid foam is listed below: 35

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Ingredient Weight parts Raw MDI 115 5 Polyol A 100

Si 1icone oil 1

Tri ethyl than i am i n 0.5

Dibutyltin dilaurate 0.1

Trichloromonofluoromethane 35

Tris (2-chloroethyl) phosphate 10

All the components except the di isocyanate are premixed, mixing the diisocyanate immediately prior to foaming and spraying with the usual equipment to form a rigid foam having an apparent density of 0.029 g / cm 3. Reduction of the amount of trichloromethane or methane foaming agent leads to density increase. Increasing the dry matter content of the preceding recipe, e.g. by adding 30 parts of methyl cellulose without increasing the amount of foam, the apparent density increases and -2q. Increased heat resistance of the foam is achieved by conventional manufacturing means and by selecting the usual ingredients, e.g. by reacting orimatic amine-containing compounds with the remaining ingredients, as described in U.S. Patent No. 25,909,465. Increased resistance to flushing, which is also desirable for the outer foam layer, can also be obtained by selecting polyol component, as described e.g. in U.S. Patent No. 3,828,257 and in U.S. Patent No. 3,928,258.

Desirable outer layers or coatings may be applied on top of the outermost insulating foam layer. The outer insulating foam layer may e.g. provided with a wrapped layer or an extruded, protective layer or a moisture-retaining layer of paper or plastic, e.g. polyethylene or polypropylene, a heat shrinkable plastic shroud or wrapper that shrinks in place and joins the foam in the sun, a coating of liquid epoxy resin, cured on site, or a coating of a bituminous pulp or layer of any other

Claims (2)

A method of producing a foamed plastic insulation coating on a tube, in particular a metal tube such as a steel tube, by applying liquid, foamable plastic layers of different density distribution over the total thickness of the plastic layers, optionally applying one or more additional materials for forming one or more additional inner layers, and the tube possibly first being further applied to a corrosion-protective coating, characterized in that at least one inner plastic layer (12) and an outer plastic layer (14) are applied one after the other on the tube (10) respectively. on one or more of the inner layers and any anti-corrosion coating and foamed to different densities where the thickness and density of the outer layer are allowed to adjust independently without external restriction, where the inner layer (12) is allowed to gain a density of 0.024-0.096 g / cm 2 and allow the outer layer (14) to have a density of at least 25% greater greater than the density of the inner layer (12) and allowing the thickness of the outer layer (14) to constitute 5-30% of the total thickness of the two plastic layers 30 (12, 14). Process according to claim 1, characterized in that polyurethane materials are used as said foamable plastics materials. 35 Process according to any one of the preceding claims, characterized in that, as the innermost layer of foamed plastic insulation, a foamable plastic material DK 151913B le is used which is stable at a temperature of up to approx. 180 ° C and foamable plastics materials which are only stable at temperatures up to about ca. 90 ° C. o 10 15 20 25 30 35