CA1160914A

CA1160914A - Insulated pipe

Info

Publication number: CA1160914A
Application number: CA000347490A
Authority: CA
Inventors: Carlos M. Samour
Original assignee: Kendall Co
Current assignee: Kendall Co
Priority date: 1979-03-15
Filing date: 1980-03-12
Publication date: 1984-01-24
Also published as: SU1351520A3; IT8020535A0; CH635182A5; PT70943A; EG14165A; DK151913C; AT377227B; JPS55133951A; HU178150B; IE800532L; SE8001923L; ES8102909A1; NO800730L; CS220765B2; ES490303A0; FR2451261B1; AR225305A1; NO161208B; AU532291B2; BE882206A

Abstract

ABSTRACT OF THE DISCLOSURE
Metal pipe insulated with foamed polyurethane plastic is made in a multi-stage continuous process in which one or more inner layers of polyure-thane plastic are foamed on the pipe and at least partially cured to form low-density foam having high heat insulating capacity, and an outer layer of polyurethane plastic is foamed on the inner layer to provide a foam layer of higher density, the outer layer having a density at least 25% greater than that of the adjacent inner layer, the thickness of the outer layer being 5 to 30% of the total thickness of the foamed insulation.

Description

This invention relates to a method of thermally insulating metal pipe and pertains more specifically to a method of providing a m~tal pipe with two or more layers of foamed plastic insulation of differin~ apparent densities and preferably different thermal stabilities, the lowest density foam being adjacent ~the surface of the pipe and the highest adjacent to the outer surface of the foamed insulation.
It has hitherto been proposed to insulate pipe by spraying thereon one or more layers of foaming plastic insulation 10 , such as polyurethane followed by curing and coating or wrapping the insulation layer with a protective or barrier layer as described for example in Bauer et al., U.S. Patent 3,480,493.
The layer of foam insulation resulting from such a process has '' normally possessed an apparent densit~ of intermediate value such 15 ll that it has properties which are a compromise between those required for maximum heat insulation characteristics and those ' required for maximum strength, crush resistance and abrasion resistance. It has also been proposed in Henderson et al., U.S.
Patent 4,094,715 to spray pipe with a foaming liquid composition, then wrap the rising foam with a protective sheet material before ; the rising foam has completely set so as to increase the density of the foam near its outermost surface. A major disadvantage of the process is that it is restricted to a spirally wound protective sheet outer layer, which is applied under tension to achieve an apparent increase in the density of the outer layer of the foam. Such a process is difficult to control in commercial operations because the extent of increase in apparent " .
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L609~4 density and the thickness of the high density layer depend upon several different critical factors including temperature of the foaming plastic, speed of foaming of the plastic composition, cure rate of the foaming plastic, time lapse before application of the protective sheet, and the tension applied to the protective sheet during application. All of these factors influence the extent to which the foamed plastic has cured or set before appli-cation of the sheet. Moreover, the thickness of the layer of increased density depends upon the thickness and compressibility of the mass of low density foam already present.
The present invention provides a method of providing metal pipe with foamed polyurethane plastic insulation which com-prises applying to said pipe a first foamable plastic composition, foaming said first composition to form a first layer of foamed plastic insulation having an apparent density from 1.5 to 6 pounds per cubic foot, then applying to the surface of the first said layer a second foamable plastic composition, foaming and curing said second composition to form a second layer of rigid foamed plastic composition having an apparent density at least 25% greater than that of the first said layer and having a thick-ness from 5% to 30% of the total thickness of both said foamed plastic layers together.
Because the thickness and density of each layer is in-dependent of the other and can be individually adjusted and con-trolled, the method of the present invention makes it possible to employ an inner layer having high heat insulation value and low cost together with an outer higher-strength and higher-density, therefore higher-cost layer. The two layers together provide combined properties which are optimal for pipe insulation and protection at minimum total cost.

~609~4 The extent of difference in density between inner and outer insulating layers for optimum results varies depending upon the diameter of the pipe, the relative thickness of the layers, the rninimum strength desired, and the temperature differential between the pipe and the surroundings, among other things.
If desired, the inner layer can be subdivided into two or more layers applied in sequence and differing in physical properties between themselves.
In the accompanying drawings, which illustrate exemplary embodiments of the preduct of the present invention:
Figure l is a view in cross-section showing one insulated pipe; and Figure 2 is a view in cross-section showing another in-sulated pipe.
In the embodiment of Figure l, metal pipe 10 is provided with an inner layer 12 of low density (2 to 6 lb/cu ft) rigid polyurethane foamed insulation having a thickness from about l to about 6 inches, and a second layer 14 of rigid polyurethane foam-ed insulation having a density at least 25% greater than that of layer 12 and having a thickness from 5 to 30% of the total thickness of layers 12 and 14 together.
In a preferred embodiment, the inner layer of foamed insulation differs from the outer layer or layers not only in having a lower apparent density and hence a higher heat in-sulation capacity, but also in having higher heat resistance, i.e., being stable at higher temperatures, up to 350F, than is the outer layer or layers of foamed insulation, which need be stable only up to a temperature of 200F.

A second embodiment is illustrated in Fig. 2 in which pipe 10, designed to carry hot fluids at temperatures of 300-350F, is provided with an inner insulation layer subdivided into a first portion or layer 20 of low density foamed polyurethane insulation formulated to have stability at a temperature as high as 350F
and a second portion or layer 22 of approximately the same low density foamed polyurethane but formulated to have stability only at temperatures up to 200F. Outer layer 24 of high density foamed polyurethane has a density at least 25% greater than that o~
either layer 20 or 22 and has a thickness from 5 to 30~ of the total thickness of layers 20, 22 and 24. In another embodiment in which pipe 10 is designed to convey cryogenic fluids at very low temperatures of the order of -200F, layer 20 is formulated to be 'Isemi-rigid instead of rigid to avoid embrittlement and possible 'Icracking during use, while layers 22 and 24 are formulated to be conventionally rigid in nature.
In practicing the method of the present invention, tne pipe, which is usually steel, is first heated to remove moisture ',condensation and cleaned to remove dirt, scale and rust. Any of the usual procedures for cleaning may be employed such as sand i blasting or shot blasting, brushing or the like. If desired, two or more of such procedures may be employed in combination.
`, In some cases, it may be desirable to provide a corrosion protective coating on the pipe surface before applying the foaming plastic to it, although this is not essential. Any ; conventional corrosion protective coating may be employed such as !
wrapped polyethylene/butyl adhesive tape, epoxy coating, heat ,activated adhesive, or asphalt. The foamable thermoplastic ma- !

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~1609i4 terial may be applied directly to the bare pipe or to the surface 'of any corrosion protective coating previously applied to the 'pipe. It is usually desirable that the temperature of the pipe be elevated above room temperature, the precise temperature depending upon the nature and composition of the foamable plastic composition. The latter is usually applied in the form of a spray 'delivered from a spray nozzle as the pipe is rotated and advanced pas~ the various nozzles. Any of a wide variety of ~formulations for the foamable liquid polyurethane plastic composition may be used depending upon the precise characteristics ';desired in the end product. A particularly desirable composition j 'is a liquid mixture of ingredients reactable to form a poly- ¦
urethane and including a conventional foaming agent in an amount l~sufficient to produce a foam having the desired apparent density, ,'which may be from about 1.5 to about 6 pounds per cubic foot. The 'first layer of foamable liquid is allowed to rise by action of the foaming agent. The thickness of the first layer of foam may vary over a wide range depending upon the same factors discussed above in connection with difference in density of the insulating layers, such as the pipe diameter and the temperature at which the`
'pipe with its contents is designed to operate, and in general may ~'vary from about 1 to about 6 inches.
The second or outer layer 14 or 24 of foamable liquid plastic composition is then applied to the outer surface of the first foamed insulation layer by spraying in the usual manner on the surface of the rotating and advancing pipe. The second layer may be applied to the first before or after the latter has been cured, and even before foaming of the latter has been completed.

Prefcrably it is applied before the first layer is cured. In one embodiment, the formulation of the second foamable plastic composition is different from the first only in the amount of foaming agent used and is adjusted so as to provide a foamed plastic insulation layer having an apparent density at least 25%
higher than that of the first layer and a thickness from 5 to 30% ¦
of the total thickness of both layers together. In another embodiment, the outer layer 14 or 24 may have a lower heat `resistance than the inner or greater rigidity or both.
I The total thickness of foamed insulation as well as the thickness of the inner layer (about 1 to about 6 inches) can be varied depending upon the temperature differential between the contents of the pipe and the surroundings of the pipe, the pipe diameter, and the apparent density of the foam, among others.
1i For a temperature difference of 75-270F, a thickness of about l to about 6 inches normally suffices. In general, the greater the temperature difference between the pipeline and the ground, the thicker the insulation should be. For example, cryogenic industries normally use 3 to 6 inches of polyurethane foam because of larger temperature differentials. For hot oil lines, the differential is usually from 100 to 160F. For hot oil pipe-! lines, the thickness would normally be from 1 to 2.5 inches. Apipe for conducting molten sulfur will be pro~ided with 2 1/2-3 inches of foamed insulation, the inner layer 12 or 20 of which is !
formulated to have high heat resistance, i.e., to be stable at temperatures up to 300F. A pipe for hot oil will when buried in ;the ground normally require a foam thickness of 2 inches or less.
Polyurethane foam has an extremely low K factor, of the order of ' i ' - 7 - I

1161)9~

0.13 Btu/sq. ft/hr/~/in., in contrast to a K factor of about 0.39 for ~lass foam. For example, in the case of a polyurethane foam having an apparent density of 3 lb/cu ft., a layer 2 inches thick on a pipe 6 inches in diameter operating at a temperature 5 differential of 125F results in a heat loss (or gain) of 5.8 Btu/hr/sq. ft. I
f There follows a suitable recipe for making a satisfactory `rigid foam:
Ingredient Parts by Weight 10 , Crude MDI 115 Polyol A 100 Silicone oil ,I Triethylene diamine 0.5 1 Dibutyl tin dilaurate 0.1 15 1l Trichloromonofluoromethane 35.
Tris(2-chloroethyl) phosphate 10.

All of the ingredients except the diisocyanate are preblended, the~
diisocyanate being mixed in immediately prior to foaming and ~spraying in conventional equipment to form a rigid foam having an apparent density of 1.8 lb/cu. ft. Decreasing the proportion of trichloromonofluoromethane blowing agent leads to increase in ~density. Increase in solids in the foregoing recipe, as by adding~
30 parts of methyl cellulose without increase in blowing agent also increases apparent density. Increased heat resistance of the ` foam is achieved by conventional formulating techniques and selection of ingredients, as for example by reacting aromatic amine-containing compounds with the remaining ingredients as described in Wiedermann et al. U.S. Patent 3,909,465; increased , , , . , , ,l - 8 ~

1~60914 , r~sistance to friability, also desirable for the outer layer of foam, can also be achieved by selection of polyol ingredients as described for example in Fuzesi et al. U.S. Patent 3,928,257 and in Alexander U.S. Patent 3,928,258.
Any desired outer layers or coatings may be applied over the outer foamed insulation layer. For example, the outer 1, foamed insulation layer can be provided with a wrapped or extruded , protective or moisture barrier layer of paper or plastic, e.g., polyethylene or polypropylene, an envelope or wrapped layer of heat-shrinkable plastic which is shrunk in place to conform to the ;foamed insulation, a coating of liquid epoxy resin cured in place or a coating of bituminous mastic, or a layer of any other conventional protective material. However, because of the tough lcrush resistant and abrasion resistant nature built into the !outermost layer of foamed polyurethane plastic in the present invention, any supplemental outer protective layer need in most cases provide only a barrier against puncture and moisture penetration. I

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Claims

1. Method of providing metal pipe with foamed polyurethane plastic insulation which comprises applying to said pipe a first foamable plastic composition, foaming said first composition to form a first layer of foamed plastic insulation having an apparent density from 1.5 to 6 pounds per cubic foot, then applying to the surface of the first said layer a second foamable plastic composition, foaming and curing said second composition to form a second layer of rigid foamed plastic composition having an apparent density at least 25% greater than that of the first said layer and having a thickness from 5% to 30% of the total thickness of both said foamed plastic layers together.

2. Method as claimed in claim 1 including the step of first applying to said metal pipe a corrosion protective coating.

3. Method as claimed in claim 2 in which said first layer of foamed plastic insulation is stable when heated to temperatures up to 350°F and said second layer is stable only to temperatures up to 200°F.

4. Method as claimed in claim 1 in which said pipe is steel and in which said first foamable plastic composition is subdivided into a first inner portion producing a foam stable when heated to temperatures up to 350°F and a second portion producing a foam stable only to temperatures up to 200°F, and said second foamable plastic composition produces a foam stable only to temperatures up to 200°F.

5. Method as claimed in any of claims 1 to 3 in which said first foamable plastic composition produces a rigid foam.

6. Method as claimed in any of claims 1 to 3 in which said first foamable plastic composition produces a semi-rigid foam.