DD149955A5 - METHOD OF PREPARING PIPES WITH PLASTIC INSULATED POLYURETHANE - Google Patents

Abstract

The invention relates to metal pipes which are insulated with foamed polyurethane. The process involves a multi-stage continuous process in which one or more internal layers of polyurethane are foamed and at least partially quenched on the pipe to obtain a low density layer with high heat-insulating capability. On the inner layer, an outer layer of polyurethane is foamed to obtain a foam layer of greater density. The density of the outer layer is at least 25% greater than that of the adjacent inner layer and the thickness of the outer layer is 5 to 30% of the total thickness of the foamed insulation.

Description

O \ 9 6 t 7 * ^ ~ Berlin, the 1 · 8 _β 1980

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Manufacturing process for pipes with plastic insulation made of foamed polyethane

Field of application of the invention

The invention relates to a method for thermal insulation of metal pipes, in particular a method for providing a metal pipe with two or more layers of a foamed plastic insulation of different apparent density values and preferably different thermal stability values, wherein the lowest density foam of the pipe surface "is adjacent and the high-density foam is disposed adjacent the outside of the foamed insulation

C characteristic of the known technical solutions

It is known to insulate pipes by spraying one or more layers of a foamable plastic insulation, eg polyurethane, and then hardening and applying or coating the insulating layer with a protective or barrier layer (see US Pat 430 493) · The foamed insulating layer obtainable by such a method normally has an apparent density of a middle value, i. h _e it has properties that represent a compromise between the properties for maximum thermal insulation and for maximum strength, fracture resistance and Abriebbeßtändigkeit, · From US-PS 4094715 there is known a tube with a ver ~ foamable liquid mass spray and then the rising foam prior to complete solidification of the rising foam with a sheet-like protective material

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The main disadvantage of this method is that it is limited to spirally wound outer protective layers applied under tension to ensure an apparent increase in the density of the outer layer of the foam "Further, such a method in practice is difficult to control, since the amount of increase in the apparent density and the thickness of the high density layer of various different critical Paktoren _s including the temperature of the foaming plastic a _s the-Verschäumungsg'eschwindigkeit the plastic mass, The curing rate of the intumescent plastic, the length of time before application of the protective film and the tension applied to the protective film during its application, depend on _e All of these factors influence the extent to which the foamed plastic is cured prior to application of the film In addition, the thickness of the layer of increased density depends on the thickness and compressibility of the mass of the already existing low-density foam.

The object of the invention is to overcome the 'difficulties and uncertainties in the insulation of the pipes',

The object of the invention is to provide a process for the thermal insulation of pipes, which ensures a good thermal insulation with a good mechanical ability, breakage resistance and abrasion resistance of the insulation.

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According to the invention, a first layer of a plastic foam consisting of foamable polyurethane is then applied to a tube and this foamed in place to form a first foamed plastic layer having an apparent density of 0.024 to 0.096 g / cm, whereupon the first foamed layer has a zv / eite layer of a foamable plastic applied and the foamable plastic is foamed in place to form a second layer of foamed plastic of high apparent density. Since the thickness and density of both layers are independent and can be individually adjusted and controlled, the method according to the invention enables a low-cost inner layer of high thermal insulation capability and an outer layer of higher strength and higher density (and thus more expensive layer). to apply. The two layers together show properties that are optimal for pipe insulation and pipe protection with minimal overall cost.

The optimum density difference between the inner insulating layer and the outer insulating layer depends, among other things, on the diameter of the tube, the relative thickness of the layers, the desired minimum strength and the temperature gradient between the tube and the environment. As a rule, however, the apparent density of the outer layer should be at least 25 % greater than the apparent density of the inner layer. The thickness of the outer layer should be 5 to 30% of the total thickness of the foamed insulating layers. Optionally, the inner layer may be subdivided into successively applied two or more layers which differ in their physical properties. "

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It is advantageous if one previously applied to the tube one or more further inner layer (s) forming masses to form one or more inner layer (s) *

It is expedient to use a metal tube, Z ₀ B, as a tube, and to apply a corrosion protection layer to the tube first.

As a foamable plastic masses v / ground preferably polyurethane compositions ver /? Reached ₀ advantageously be an innermost layer of foamed plastic insulation which is stable up to temperatures of 177 ° C, and (a) outer layer (s) _t is the only up to temperatures of 93 s5 ⁰ C stable (is), manufactures.

β ¹

It is possible to provide a rigid layer as the innermost layer ^ so that a semi-rigid layer can be provided as the innermost layer. "

The invention is explained in more detail below with reference to the drawings

Figo 1ϊ a cross section through an embodiment of an inventive insulated pipe and

Pig. 2% shows a cross section through another embodiment of an insulated pipe according to the invention »

1, a metal tube 10 having an inner insulating layer 12 of low density (0.032 to 0.096 g / cm ³ ) of hard polyurethane foam of a thickness of about 2.54 to 15 »24 cm and a second insulating layer 14 made of hard polyurethane foam.

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polyurethane foam of a density which is at least 25 % greater than the density of the inner insulating layer 12, and a thickness which is 5 "to 30 % of the total thickness of the layers 12 land 14 together provided.

Preferably, the inner foamed insulating layer of the outer layer or outer layers should be foamed not only by lower apparent density and hence higher heat insulating ability but also higher heat resistance (higher temperature stability up to 177 ^° C.) than the outer one Insulate or outer foamed insulating layers (which need only be stable up to 93.3 ° C) (have) distinguish. '.

In the embodiment shown in Figure 2, a tube 10, in which hot liquids are to be transported at temperatures of 149-177 ⁰ C, with an inner insulating layer, in a first insulating part or a first insulating layer 20 of low density foamed polyurethane (a Stability up to a temperature of 177 ° C) and a second insulating part or a second insulating layer 22 from about the same low-density polyurethane foam (a stability up to only 93.3 C) is divided provided. The outer layer 24 of high density polyurethane foam has a density which is at least 25 % greater than the density of the layers 20 and 22, and a thickness corresponding to 5 to 30% of the total thickness of the layers 20, 22 and 24.

In a further embodiment, a tube 10, which is used to transport cryogenic liquids at very low temperatures.

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is intended temperatures in the order of -129 ⁰ G, be ~ is the layer 20 of a semi-rigid foam instead of a hard foam, to avoid Brösligwerden and possible cracking during use, "The layers 22 and 24 may, however, as usual , made of hard foam *

In carrying out the method according to the invention, the usually made of steel pipe is first heated to remove condensation moisture _s and cleaned to remove dirt, stone foundation and rust »For cleaning one can commonly known methods, eg < ₀ sandblasting or Shot blasting ^ brushing and the like, operate * If necessary, two or more cleaning measures can be used in combination ©

In some cases it may be expedient to provide the pipe surface with a corrosion protection coating or * an anticorrosive coating prior to application of the foamed plastic coatings. * However, this is not absolutely necessary «. Conventional corrosion protection coatings or layers, e.g. _o B * wrapping material made of polyethylene / Butylklebstreifen, epoxy coatings, heat-activated adhesives or asphalt * The foamable thermoplastic material may be any one directly on the bare pipe or on the surface of previously applied corrosion protection coating can be applied in this case be applied "in the It is usually advisable to raise the temperature of the tube to above room temperature. * The whole temperature depends on the nature and composition of the foamable plastic compound. The latter is usually applied to the rotating and the rotating surfaces by means of a spray nozzle

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Depending on the desired properties of the end product, one can use the most varied formulations of foamable liquid polyurethane plastics. A particularly suitable composition consists of a liquid mixture of constituents reacting with one another to form a polyurethane which contains so much common blowing agent. The first layer of the foamable liquid is allowed to rise with the aid of the blowing agent. The thickness of the first foam layer may vary depending on the density difference of the insulating layers The factors discussed, eg pipe diameter and temperature at which the filled pipe should be operational, can vary widely. Typically, it can range from about 2.54 bi3 to 15.2 cm.

Thereafter, the second or outer layer 14 or # 24 of the foamable liquid plastic mass is applied to the outside of the first foamed insulating layer 16. This is done by conventional spraying on the surface of the rotating and advancing tube β Preferably, it is applied before the first layer is cured. In an advantageous embodiment, the formulation of the second foamable plastic composition differs from the formulation of the first only in the first layer Amount of propellant used «This is adjusted so that a foamed plastic

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insulating layer of apparent density at least 25 % larger than the apparent density of the first layer, and a thickness constituting 5 to 30 % of the total thickness of the two layers together. In another advantageous embodiment, the outer layer may be 14 or 24 have a lower Y / heat resistance and / or be harder than the inner layer

The overall thickness of the foamed insulation as well as the thickness of the inner layer (about 2.54 to 15 "24 cm) may vary greatly depending, inter alia, on the temperature gradient between the tube contents and the tube environment, the tube diameter and the apparent density of the foam "At a temperature gradient of 23" 8 to 132.5 ° C, a thickness of about 2.54 to 15 ".24 cm is usually sufficient. As a rule, should be made thicker with increasing temperature difference between the pipe and the bottom of the isolation "generally need at low temperatures working industries normalerv / else 7" β to 15j24 cm thick polyurethane foam layers, as larger temperature gradients prevail _e In hot oil lines the temperature gradient is in usually 37 * 7-71.2 ⁰ C * with hot oil pipelines, the thickness should normally have a 6.3-7 2.54 * 65 cm thick foamed insulation to β j, 4 cm should be © a pipe for molten sulfur, where the inner layer should be designed 12 or © 20 to a higher heat resistance (up zn temperatures of 149 ⁰ C) pipes, hot oil, which are g require buried in the ground typically a foam thickness of 5 * 1 cm or less " Polyurethane foam has an extremely low K factor on the order of about 6 _? 94 x 10 g-cal / cm / s / ° C / cm in contrast to the triple value for glass foam <> one

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Poljrureth.ansch.room an apparent thickness of 0.048 g / cnP in the form of a 5 x 1 cm thick layer on a tube of a diameter of 15.24, which operates at a temperature gradient of 69 »4 ⁰ C causes heat loss or gain of about 43.7 x 10 "g-cal / cm ·

An acceptable rigid foam can be produced using the following recipe:

parts by weight 5 115 1 100 1 O, O, 35 10

Crude MDI polyol A

Silicone1. "

Triethylenediamine dibutyltin dilaurate trichloromonofluoromethane tris (2-chloroethyl) phosphate

All ingredients except the diisocyanate are premixed and the diisocyanate is mixed immediately before foaming, after which the whole is sprayed in a conventional apparatus for producing rigid foams of apparent density of 0.029 g / cm. A reduction in the amount of trichloromonofluoromethane propellant leads to an increase in density. An increase in the level of the substance in the formulation given, for example by adding 30 parts of methylcellulose, without increasing the amount of blowing agent also leads to an increase in the apparent density. An increased heat resistance of the foam can be achieved by conventional formulation measures and by conventional choice of ingredients, for example by reacting aromatic amine-containing compounds with the

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remaining constituents (see US Pat. No. 3,909,465). Improved resistance to browning, which is particularly desirable for the outer foaming layer, is achieved by appropriate choice of the polyol components (see U.S. Patents 3,928,257 and 3,928,258) _β

Any outer layers or coatings can be applied · For example, the outer foamed insulation layer having a wound or exfcrudierten protective layer or moisture barrier layer of paper or plastic, for _a B ^ ₆ polyethylene, or polypropylene on the outer foamed insulation, a sheath or a wound layer of a heat shrinkable plastic which is shrunk in place in adaptation to the foamed insulation, a coating of a liquid epoxy resin that is cured in place _s or a coating of a bituminous mastic, or a layer of any other protective material Due to the extremely tough, break-resistant and abrasion-resistant nature of the outermost layer of foamed polyurthane plastic, additional outer layers in most cases only need a barrier against sting and the ingress of moisture to deliver"

Claims (1)

invention claim 1 · Method of manufacturing pipes with plastic insulation of foamed polyurethane by forming at least one inner layer and an outer layer of a foamed plastic insulation, characterized in that applied to the tube at least one inner layer deliverable foamable plastic mass, the or «each mass to form a foamed layer of foamed plastic insulation having an apparent density of 0.024 to 0.096 g / cm foamed, then applied to the surface of the last applied inner layer, an outer layer forming foamable plastic compound and foamed and used to form an outer layer mass foams, an outer layer of foamed hard plastic of apparent density at least 25 % greater than the apparent density of the inner layer (s) and having a thickness of 5 to 30 % of the total thickness of all the layers together t " 2 # The method according to item 1, characterized in that one or more v / eere inner layer (s) forming masses previously applied to the tube to form one or more v / eiterer inner layer (s) » 3 · Method according to one of the items .1 or 2, characterized in that a metal tube, eg. B »uses a steel pipe and first applies a corrosion protection layer to the pipe» 4. Process according to one or more of the preceding points, characterized in that polyurethane is used as foamable plastic compounds. « «-Ι * vs / _ ₁₂ " ^ 1 * 8 * 1980 57,119 / 17 β "Process according to one or more of the preceding" points, characterized in that an innermost layer of foamed plastic insulation, which is stable up to temperatures of 177 ⁰ C, and (an) outer layer (s), which only up to temperatures of 93 »5 stable (is) produced 6 «Method according to one or more of the preceding points, characterized in that the innermost layer is provided by a rigid layer« Method according to one or more of the items 1 to 5, characterized in that the innermost layer is provided by a "semirigid layer" For this 1 page drawings