IT8020535A1 - PROCEDURE FOR INSULATING DUCTS - Google Patents

Description

PROCEDURE FOR INSULATING DUCTS

SUMMARY

A metal conduit insulated with expanded polyurethane plastic knows? done in a continuous multi-stage process in which one or more? Inner layers of polyurethane plastic are expanded on the conduit and are at least partially cured to form a low density foam. having a high capacity? of insulation, and an outer layer of polyurethane plastic is expanded over the inner layer to provide a layer of high density foam, the outer layer having a high density. greater than at least 25% of that of the adjacent inner layer, the thickness of the outer layer being 5 to 30% of the total thickness of the expanded insulation.

DESCRIPTION

The present invention relates to a process for thermally insulating a metal conduit and relates to more? specifically a pr? failure capable of providing a metal conduit with two or more? layers of expanded plastic insulation of different densities apparent and preferably different stabilities? thermal, the foam having the density? pi? low being adjacent to the surface of the duct and the density? pi? elevated being adjacent to the outer surface of the expanded insulation.

Up to now it has been proposed to isolate a duct by spraying one or more of it. foaming plastic insulation layers such as polyurethane followed by polymerization or hardening and coating or wrapping the insulation layer with a protective or barrier layer as described for example in Bauer et al., U.S. Pat. 3,480,495. The foam insulation layer resulting from such a process normally had a high density? apparent of an intermediate value so that it had properties? representing a compromise between those required for maximum thermal insulation characteristics and those required for maximum strength, shatter resistance and abrasion resistance. In Henderson et al., U.S. Pat. 4? 094? 715? It has also been proposed to spray the duct with a liquid foam-forming composition, then wrap the growing foam with a protective foil-like material before the growing foam is completely cured in order to increase the density. of the foam in the vicinity of its outer surface. A major drawback of the process? what it? limited to an outer layer in the form of a spiral-wound protective sheet which? applied under tension to obtain a noticeable increase in density? of the outer layer of the foam. Such a procedure? difficult to control in the operations trades them since? the measure of the increase in density? apparent and the thick king of the high-density layer? depend on several critical factors including the temperature of the foaming plastic, the fast t? foaming of the plastic composition, the fast t? of polymerization of the foam plastic, the length of time prior to application of the protective sheet, and the tension applied to the protective sheet during application. All of these factors affect the degree of polymerization or hardening of the foam before the application of the sheet. In addition, the thickness of the layer of increased density? depends on the thickness of the low-density foam mass? already? present and the extent to which it can? come compressed.

The present invention provides a method for applying a first layer of polyurethane plastic composition to a conduit which can be expanded and its expansion in place to form a first layer of low density foam plastic. apparent, from 1.5 to 6 pounds / cubic foot (from about 0.024 to 0.096 g / cm3), then applying a second layer of foam-forming plastic to said first layer and expanding it in place to form a second layer of foam plastic having a high density? apparent.

Since? the thickness and density? of each layer are independent of each other and can be individually regulated and controlled, the process of the present invention allows the use of an internal layer having a high thermal insulation value and low cost in combination with an external layer with higher resistance. high and density? pi? high, therefore the cost more? high. The two layers together provide properties? combinations that are optimal for insulation and for the protection of a duct at a minimum overall cost.

The degree of difference in density? between the layers of internal and external insulation necessary for optimal results varies over centuries from, among other things, the diameter of the duct, the relative thickness of the layers, the minimum desired resistance, and the temperature gradient between the duct and the environment. . However, in general, the density? The apparent thickness of the outer layer must be at least 25% greater than that of the inner layer, and the thickness of the outer layer must be 5 to 30% of the total thickness of the insulating foam layers. If desired, the inner layer can? be divided into two or more? layers applied in sequence and which have differences in properties? physical between them. In the drawings:

fig. 1? a cross sectional view showing an embodiment of the invention; And

fig. 2 ? a cross-sectional view showing another embodiment.

In the embodiment of FIG. 1, the metal conduit 10? supplied with an internal low density 12 layer? (2 to 6 pounds / cubic foot or 0.032 to 0.096 g / cm) of rigid polyurethane foam insulation having a thickness of about 1 to about 6 inches (2.54 to 15.24 cm), and a second layer 14 of rigid polyurethane foam insulation having a density of at least 25% greater than that of layer 12 and having a thickness of 5 to 30% of the total thickness of layers 12 and 14 together.

In a preferred embodiment of the invention, the stra. internal foam insulation? different from the outer layer or from the outer layers not only because? has a density? apparent pi? low and therefore a capacity? of thermal insulation pi? high, but also why? has a thermal resistance pi? high, that is? ? stable at temperatures more? high, up to 350? F (177? C), of what? the outer layer or layers of expanded insulation, which need only be stable up to a temperature of 200? F (93.5? 0).

A second form of execution? illustrated in fig. 2, in which conduit 10, designed to carry hot fluids at temperatures of 300 to 350 ° F (149 to 177 ° C),? provided with an internal insulation layer divided into a first portion or layer 20 of low density expanded polyurethane insulation. formulated to be stable at temperatures up to 350? F (177? C) and a second portion or layer 22 from approximately the same low-density polyurethane foam. but formulated to be stable at temperatures only up to 200? F (93.5? 0). The outer layer 24 of high density polyurethane foam has a density? at least 25% greater than that of layer 20 or 22 and has a thickness of 5 to 50% of the total thickness of layers 20, 22 and 24. In another embodiment where the conduit 10 is designed to carry cryogenic fluids at very low temperatures of the order of -200? F (-129? C), the layer 20? formulated to be semi-rigid instead of rigid to avoid embrittlement and possible splitting during use, while layers 22 and 24 are formulated to be conventionally rigid in nature.

In practicing the process of the present invention, the conduit, which? usually steel, is first heated to remove humidity? condensed and is cleaned to remove dirt, scab and rust. Pu? any of the usual methods for cleaning such as sandblasting or shot peening, brushing or the like can be employed. If desired, two or more can be used. of these processes in combination.

In some cases, it can? It may be desirable to provide a protective anticorrosive coating on the surface of the duct prior to applying the foam-forming plastic thereon, although this is not the case. is not essential. Any conventional anticorrosive protective coating can? be employed such as polyethylene / butyl wrapped adhesive tape, epoxy coating, hot-melt active adhesive, or asphalt. The thermoplastic material which can? be expanded can? be applied directly to the bare duct or to the surface of any anticorrosive protective coating previously applied to the duct. It is usually desirable that the temperature of the duct be higher. high ambient temperature, the exact temperature depending on the nature and composition of the foam-forming plastic composition. The latter? usually applied in the form of a spray delivered from a spray nozzle as the conduit is rotated and advanced in front of various nozzles. Any one of a wide variety of suitable formulations for the liquid polyurethane foam-forming plastic composition pu? be used according to the precise characteristics desired in the final product. A particularly desirable composition? a liquid blend of ingredients which can react to form polyurethane and including a conventional foaming agent in an amount of sufficient to produce a foam having the desired density. apparent, what can? be about 1.5 to about 6 pounds per cubic foot (0.024 to 0.096 g / cm). The first layer of foaming liquid? allowed to grow by the action of the foaming agent. The thickness of the first layer of foam can? vary over a wide interval depending on the same factors discussed above with reference to the difference in density? of the insulating layers, such as diameter of the duct and the temperature at which the duct with the BUO content? intended to operate, and in general can? varies from about 1 to about 6 inches (2.54 to 15.24 cm).

The second layer or outer layer 14 or 24 of foaming liquid plastic composition is then applied to the outer surface of the first foam insulating layer by spraying in a conventional manner on the surface of the rotating and advancing conduit. The second layer can? be applied on the first before or after the latter? been cured and even before the completion of foaming of the latter. Preferably it? applied before curing of the first layer. In one embodiment, the formulation of the second foam-forming plastic composition? different from the first only as regards the quantity? of foaming agent used and? adjusted in such a way as to provide an expanded plastio insulation layer having a density? apparent greater than at least 25% of that of the first layer and a thickness of 5 to 30% of the total thickness of both layers together. In another embodiment, the outer layer 14 or 24 can have a higher thermal resistance? low of the inner layer or stiffness? pi? high or both.

The total thickness of expanded insulation as well as the thickness of the inner layer (about 1 to 6 inches or about 2.54 to 15.24 cm) may vary, among other things, according to the difference or the temperature gradient between the contents of the duct and the external environment, the diameter of the duct, and the density? apparent foam. For a temperature difference of 75 to 270? F (41.5 to 150? C) a thickness of about 1 to about 6 inches (2.54 to 15.24 cm)? normally sufficient. In general, how much greater? the difference in temperature between the pipeline and the ground, the more? often it must be isolation. For example, cryogenic industries normally use 3 to 6 inches (7.6 to 15.24 cm) of polyurethane foam due to the smaller sizes. large differences in temperatures.

For hot oil ducts, the difference? usually 100 to 160? F

(55.5 to 89? C). For hot oil pipelines, the thickness should normally be 1 to 2.5 inches (2.54 to 6.4 cm). A conduit suitable for carrying molten sulfur will be? provided with expanded insulation having a thickness of 2.5 to 3 inches (6.3 to 7.35 cm), the inner layer 12 or 20 of which is formulated to exhibit high thermal resistance, i.e. so as to be stable at temperatures up to 300? F (149? C). A hot oil line will require? normally, when buried, a foam thickness of 2 inches (5.1 cm)

or less. Polyurethane foam has an extremely low K-factor, on the order of 0.13 Btu / square foot / hour /? F / inch

, in contrast to a K-factor of approx

0.39 for the glass foam. For example, in the case of a polyurethane foam having a density? apparent of 3 pounds / cubic foot

(0.048 g / cm3), a 2 inch (5.1 cm) thick layer on a conduit having a diameter of 6 inches (15.24 cm) operating at a temperature difference of 125? F (69.4? 0) leads to a heat loss (or gain) of 5.8 Btu / hour / square foot

Below is a recipe for making a satisfyingly rigid foam

from:

All ingredients except the dylsocyanate are pre-mixed, the diisocyanate being added and mixed immediately prior to foaming and spraying in conventional equipment to form a rigid foam having a density. apparent of 1.8 lbs / cubic foot (0.029 g / cm). The decrease in the proportion of the expanding agent of trichloromonofluoromethane leads to an increase in density. Increasing the solids in the above recipe, such as by adding 30 parts of methyl cellulose without increasing the blowing agent also increases the density. apparent. The increased thermal resistance of the foam is achieved by conventional formulation techniques and by selection of ingredients, such as by reacting compounds containing aromatic animins with the remaining ingredients as described in Wiedermann et al. U.S. Patent 3,909,465; the increased resistance to friabi lit?, also desirable for the foam of the outer layer, can? also be achieved by selecting polyol ingredients as described for example in Fuzesi et al. U.S. Patent No. 3,928,257 and in Alexander U.S. Pat. No. 3,928,258.

Outer layers or coatings of any desired type can be applied on the outer foamed insulating layer. For example, the outer layer of expanded insulation can? be provided with a protective layer or barrier against humidity? wrapped or extruded of paper or plastic, for example, polyethylene or polypropylene, a wrapped or wrapped layer of heat shrinkable plastic which? shrunk in place to conform to the foam insulation, a cured liquid epoxy resin liner in place or a bituminous mastic liner, or a layer of any other conventional protective material. However, due to the highly shatter-resistant and abrasion-resistant nature incorporated in the outer layer of the polyurethane foam in the present invention, any additional outer protective layer must, in most cases, only provide a barrier against perforation and penetration. humidity

Claims (8)

1. A process for providing a conduit with at least one inner layer and an outer layer of foamed insulating plastic, which comprises applying to said conduit at least one plastic composition capable of expanding forming an inner layer, expanding said composition or each composition for forming a respective foamed plastic insulation layer having a density apparent from 0.5 to 6.0 pounds / cubic foot (0.024 to 0.029 g / cm3), applying a composition of pia. capable of expanding forming an outer layer and expanding and polymerizing the composition forming the outer layer to form an outer layer of rigid foam plastic composition having a density. apparent at least 25% greater than that of the inner layer or any inner layer, and having a thickness of 5 to 30% of the total thickness of the layers. 2. A method according to claim 1 further comprising previously applying to the duct one or more? further inner layer forming compositions to form one or more? further inner layers. Method according to claim 1 or 2, wherein the conduit? a metal conduit, such as a steel conduit, and further comprising the initial application of an anticorrosive protective coating to the conduit. 4 Process according to any one of the preceding claims, in which the plastic compositions capable of being foamed are polyurethane compositions. 5 Process according to any one of the preceding claims in which the layer pi? internal foam plastic insulation? stable temperatures up to 350? F (177? C) and the outer layer or outer layers are only stable up to temperatures of 200? F (93.5? C). 6. Process according to any one of the preceding claims, in which the pi? internal ? stiff. 7. Process according to any one of claims 1 to 5, wherein the layer pi? internal ? semi rigid. 8. Conducted when isolated by the method according to any one of the preceding claims.