NL8001541A - METHOD FOR INSULATING PIPE. - Google Patents

Description

VO 019U

Method of insulating pipe.

The invention relates to a method of thermally insulating metal pipe, more particularly a method of providing a metal pipe with two or more layers of insulating plastic foam with a different apparent density and preferably a different thermal stability, wherein the lowest density foam is adjacent to the surface of the pipe and the highest density foam is located at the outer surface of the insulating foam.

It has hitherto been proposed to insulate pipe by spraying one or more layers of insulating plastic foam such as polyurethane thereon, followed by curing and coating or wrapping the insulating layer with a protective layer or barrier, as described, for example, in the US patent. -sehrift 3 1 + 80 U93. The layer of insulating foam resulting from such a treatment has an average apparent density such that the properties lie between those having maximum heat-insulating properties and those required for maximum strength, and resistance to breaking and abrasion. According to US patent h 09k 715, it is proposed to spray liquid foam composition on a pipe, and to coat the swelling foam with a protective sheet material before the foam is fully cured, thereby increasing the density of the foam near the outer surface. A major drawback of this method is that it is limited to a spiral wound protective outer layer, which is applied under tensile stress to increase the apparent density of the outer foam layer. Such a process is difficult to control on a commercial basis since the extent of the increase in the apparent density and the thickness of the higher density layer depends on various critical factors, such as, for example, the temperature of the plastic foam, the speed within which the plastic composition foams, the hardening speed of the plastic foam, the time that elapses before the protective layer is applied, and the tensile stress which is applied to the protective layer during its application. All these factors influence the moment when the foam has hardened or worked before the protective layer is applied. Moreover, the thickness of the high-density layer depends on the thickness and compressibility of the low-density foam mass already present.

The invention provides a method of applying a first layer of polyurethane art foam composition to a pipe which foams on site to form a layer of lower apparent density (about 0.02U to 0.096g / ci) after which about · this first layer is applied to a second layer of plastic which foams on site to form a second layer with a high apparent density.

Since the thickness and density of each layer is dependent on the others and can be individually adjusted and controlled, the method of the invention makes it possible to use an inner layer with a high heat insulation value which is inexpensive together with an outer stronger layer with a higher density, which is generally more expensive.

The two layers together provide combined properties that are optimal for pipe insulation and protection, keeping overall costs to a minimum.

The difference in density between the inner and the outer insulating layer for obtaining maximum results can vary depending on the diameter of the pipe, the relative thickness of the layers, the minimum required strength and the temperature difference between the pipe and the environment, for example .

In general, the apparent density of the outer layer is at least 25% greater than that of the inner layer, while the thickness of the outer layer is 5 to 30% of the total thickness of the insulating foam layers together. Optionally, the inner layer can be divided into two or more layers which are applied one after the other BAD0R, Wb 15 41 3 and which can differ in properties.

The invention is further elucidated with reference to the drawing. In the drawing: Fig. 1 shows a cross section of an insulated pipe according to the invention; and Fig. 2 is a cross section of another embodiment.

In Fig. 1, a metal pipe 10 is provided with an inner layer 12 of rigid insulating polyurethane foam of

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Low density (0.032 to 0.096 g / cm) with a thickness of about 2.5 to 15.21; cm and a second layer 1U of rigid polyurethane insulating foam with a density 25 # greater than that of the layer 12 with a thickness of 5 to 30 # of the total thickness of the layers 12 and 1U together.

According to a preferred embodiment of the invention, the "inner insulating foam layer differs from the outer layer or layers not only in terms of a lower apparent density and thus a greater heat insulating capacity, but also in terms of greater heat resistance, i.e.

The foam is at higher temperatures (177 ° C) than the outer layer or layers of insulating foam which need only be stable at a temperature of 93.5 ° C.

In the second embodiment, shown in Fig. 2, the pipe 10 is intended to transport hot liquids at a temperature between 1U-9 and 177 ° C, which pipe is provided with an inner insulating layer which is divided into a first layer 20 of insulating polyurethane foam of low density and a stability at a temperature of 177 ° C and a second layer 22 of approximately the same polyurethane foam of low density, but composed such that it is only stable at a temperature of 93.5 ° C. The outer layer 2h of polyurethane foam has a density which is at least 25 # greater than that of the other layers 20 or 22 with a thickness of 5 to 30 # of the total thickness of the layers 20, 22 and 2k together. When the pipe BAD ORIGglflLO f 5 4 1 k 10 has to transport a fluid at a very low temperature (-129 ° C), the layer 20 is less rigid to avoid chipping and cracking during use, while layers 22 and 2k are the usual have stiffness.

The method according to the invention proceeds as follows. The pipe, which normally consists of steel, is first heated to remove moisture and condensation and then cleaned to remove dirt, hammer and rust. Any conventional cleaning operation may be applied such as sandblasting or otherwise, brushing or the like . Optionally, two or more such operations can be used in combination.

Under certain circumstances, it may be desirable to apply an anti-rust coating to the pipe surface before the plastic foam is applied thereon, although this is not essential. Any conventional anti-corrosive coating can be used such as polyethylene / butyl adhesive tape, epoxy layers, hot tack adhesive, or asphalt.

The plastic material to be foamed can be applied directly to the bare pipe or to the anti-rust coating, if it is located on the pipe. The temperature of the pipe is kept above room temperature, the correct temperature depending on the nature and composition of the composition to be foamed. The foam is normally applied in the form of a jet from a spray nozzle while the pipe is rotated and moved along different nozzles. Different composition for the liquid polyurethane synthetic foam can be used depending on the properties that the end product must have.

A very desirable composition is a liquid mixture of reactive substances to form polyurethane with a foaming agent to obtain a foam of the desired apparent density ranging from 0.024 to 0.096 g / cm.

The first layer of foamable liquid forms under the influence of the foaming agent.

The thickness of the first layer of foam can vary greatly depending on the conditions discussed above in conjunction with the difference in density of the insulating layers, including the pipe diameter and the temperature at which the pipe is to function, generally it is between 2.5¼ and 15.2¼ cm.

The second or outer layer 1¼ or 2¼ of liquid foaming agent is then applied to the outer surface of the first insulating layer by spraying it onto the surface of the rotating pipe and the moving pipe. The second layer is applied to the first after it has cured, sometimes before the shifting is completed. Preferably, the layer is applied before the first layer has hardened. The composition of the second layer of plastic foam differs from that of the first substantially 15 in the amount of foaming agent used which is adjustable to obtain an insulating foam layer of the desired apparent density that is at least 25% higher than that of the first layer with a thickness of 5 to 30% of the total thickness of the two layers together. According to another embodiment, the outer layer can have 1¼ or 2¼ lower resistance to heat than the inner layer or greater stiffness, or both.

• The total thickness of the insulating foam as well as the thickness of the inner layer (approximately 2.5¼ to 15.2¼ cm) can vary depending on the temperature difference between the contents of the pipe and the environment, the pipe diameter and the apparent density of the foam, for example.

For a temperature difference between 23 ° S and 132.5 ° C, a thickness of about 2.5b to 15.2¼cm is sufficient.

30 The larger the temperature difference in general between a pipeline and the ground, the thicker the insulation must be.

In the cooling technique, layers from 7.6 to 15.2 .2. cm polyurethane foam used due to larger temperature differences.

The temperature difference in the transportation of hot oil is 3T, 7 ° C

BAD ORIGIfg ^ 0 15 41 6 to 71.2 ° C. The thickness is then normally 2.51+ to 6.1 cm. A pipe for transporting molten sulfur has an insulating layer of 6.3 to 7.65 cm, the inner layer 12 or 20 having a high resistance to heat, for example, it is stable at a temperature of -5 ”up to 11 + 9 ° C . A hot oil pipe to be laid in the ground requires a foam thickness of 5.1 cm or less. Polyurethane foam has an extremely low K factor on the order of 6.9b x 10 “g-cal / cm 2 / sec / ° C / cm, as opposed to a K factor of van.39 for glass foam.

10 In the case of polyurethane foam of apparent density

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of 0.0 ^ 8 g / cm, the layer is 5.1 cm thick on a pipe 15.21+ cm in diameter operating at a temperature difference of 51.7 ° C

resulting in a heat loss of about 1 + 3.7 x 10 µ gcal / 20 cm / sec / C / cm. A suitable composition for making a sufficiently strong foam is as follows:

Composition Parts by weight of raw MDI 115

Polyol A 100

Silicone oil 1 20 Triethylenediamine 0.5

Dibutyltin dilaurate 0.1

Trichloronofluoromethane. 35.0

Tris (2-chloroethyl) phosphate 10.0

All of these ingredients except the diisocyanate are premixed, with the diisocyanate being mixed immediately before foaming and sprayed in a conventional manner with an appropriate installation to form a strong foam with an apparent density of 0.029 g / cm. Decreasing the amount of trichloronofluoro-methane leads to an increase in density. Increasing the solid by admixing 30 particles of methyl cellulose without increasing the blowing agent also increases the density.

Greater heat resistance of the foam is obtained BAD ORIgMiP 15 41 7 by conventional measures and the selection of the constituent parts, for example, by reacting aromatic amine-containing compositions with the other materials as described in U.S. Patent 3,909 U65; increased resistance to crumbling as desired for the outer foam layer can be obtained by the selection of polyol as disclosed in U.S. Pat. Nos. 3,928,257 and 3,928,258.

Any desired covering can be applied over the outer insulating foam layer. The outer insulating foam layer can, for example, be provided with an extruded protective or moisture-resistant layer of paper or plastic, for example polyethylene or polypropylene, a coating or wrapping of heat-shrinking plastic and can replace the outer foam layer, a coating of liquid epoxy resin which hardens in situ or a coating of bituminous mass or a layer of another conventional protective material. Although the polyurethane plastic in the outer layer has a great resistance to tearing and wear, in many cases a protective layer is still applied as a barrier against sharp objects and moisture penetration.

BAD originSiP 0 15 41

Claims (6)

1. A method for applying at least an inner and an outer layer of insulating plastic foam to a pipe, wherein at least one inner layer of foamable plastic is applied to the pipe, after which the layer is foamed to an apparent thickness of 0.021 ; up to 0.096 g / cm, on the last applied inner layer an outer layer of a foamable plastic composition is applied, this layer is foamed and hardened to form a strong plastic layer with an apparent density which is at least 25% greater than that of an inner layer with a thickness of 5 to 30% of the total thickness of the layers. A method according to claim 1, characterized in that one or more inner layers are applied to the pipe to form an inner composite layer. Method according to claims 1-2, characterized in that the pipe consists of metal, such as steel, on which a rust-resistant coating is applied. k. Method according to claims 1-3, characterized in that the foamable plastic composition is polyurethane. 5. Method according to claims 1 - characterized in that the inner layer of foamed insulating plastic is stable at a temperature of up to 17 ° C, while the outer layer or the outer layers are only stable at a temperature of 93.5 ° C. 6. A method according to claims 1-5, characterized in that the inner layer is a rigid layer. A method according to claims 1-5, characterized in that the inner layer is a semi-rigid layer. 8. Pipe or the like provided with an insulation applied using the method according to claims 1 - 7. BAD ORIG $ lJft_ ^ 15 41