WO1999009346A1

WO1999009346A1 - A thermally insulating cover structure, a pipeline using said cover structure and a method for providing a pipeline with said cover structure

Info

Publication number: WO1999009346A1
Application number: PCT/DK1997/000331
Authority: WO
Inventors: Vagn Korsgaard
Original assignee: Hygrowick-International ApS
Current assignee: Hygrowick-International ApS
Priority date: 1997-08-15
Filing date: 1997-08-15
Publication date: 1999-02-25
Anticipated expiration: 2000-02-15
Also published as: EP1002207A1; AU3847197A; US6635322B1

Abstract

A thermally insulating cover structure adapted for covering a hot pipe comprises a heat insulation layer (2), a filler layer (3) and a jacketing (6), which is provided with drain openings (5). The filler layer comprises a material which is permeable to water. The drain openings are shielded against entry of water, while they allow drainage of water from the filler layer into the environment. This cover structure is in particular suited for outdoor pipelines, where moist conditions may arise. The invention also provides a pipeline and a method of providing a pipeline with a thermally insulating cover structure.

Description

A THERMALLY INSULATING COVER STRUCTURE, A PIPELINE USING SAID COVER STRUCTURE AND A METHOD FOR PROVIDING A PIPELINE WITH SAID COVER STRUCTURE

The present invention relates to a thermally insulating cover structure for covering a heated body, such as a pipe, a vessel, a tank, a valve or a fitting, which structure comprises a layer of heat insulation material covering the body and a jacketing or sheathing adapted for protecting the heat insulation material against the ingress of water. 0

The invention further relates to a pipeline adapted for carrying a heated fluid and to a method of providing a pipe with a thermally insulating cover structure.

5 The heat insulation material serves the purpose of reducing the cost of energy needed to keep the body at the desired elevated temperature as well as the purpose of reducing the heat stress applied to the surroundings. The jacketing provides protection against ingress of 0 water and mechanical protection. Water or moisture inside the heat insulation is highly undesirable as it is an immediate cause of reduced thermal performance of the insulation and over time a major cause of corrosion of structural components and a cause of degradation of the 5 insulation material.

This type of cover structure is in particular adapted for environments, where precautions against external influences such as outdoor climate, excessive humidity or 0 mechanical loads are required. The invention is in particular, although not exclusively, useful for applications where the structure is subject to varying temperatures. This may e.g. be the case with an outdoor pipelines subject to intermittent heating due to 5 intermittent service in carrying of heated fluids. Varying temperatures in the structure may also arise in structures in continuous service due to external factors e.g. sunshine, rain, wind, splashing with water etc. These are circumstances which may prevail on pipelines installed in oil refineries, oil transportation and storage facilities, chemical processing plants etc.

It is widely believed that an insulation structure covering a body subject to a temperature exceeding the temperature of the surroundings will stay dry, as the heat dissipated from the body is presumed to evaporate and drive away any moisture from the insulation structure through unavoidable openings in the protection layer. However, inspections on pipeline structures subsequent to some time of service have sometimes revealed moisture or water inside the insulation material in quantities far exceeding what was expected and what could be explained. Inspections on pipeline structures have also sometimes revealed premature corrosion.

The inventor has discovered that these phenomena can be explained by the following considerations. During a phase of decreasing temperature inside the jacketing, air will be sucked from the surroundings and through openings in the jacketing into the insulation material. As this air will meet decreasing temperatures, the relative humidity will rise and droplets of condensed water may form at the coldest spots encountered, wherever they may be. As the insulation material is not very permeable to water, at least in its undegraded state, it will tend to confine any condensed water to stay where it is. On moist conditions in the environment, a film of water may also have been formed on the outside of the sheath, which film represents a further source from which water may be conveyed into the interior of the insulation structure along with any air sucked in. During a subsequent phase of increasing temperature in zones of the insulation material containing liquid water, water may evaporate and may move along with the air, the insulation material being generally highly permeable to vapour and air. Some air may leave the insulation structure, possibly carrying some vapour with it. Should the air, however, before exciting the insulation structure happen to pass a zone with a relatively lower temperature, it is likely that some of the moisture will condense and stay there.

In case of an outdoor pipeline temporarily not being used, it is e.g. likely that moist air will move into the insulation material during night time, depositing droplets of water on the inside of the sheath. During daytime, the jacketing heats up and water evaporates and moves along. As the pipe is now likely to be the coldest part, it will tend to accumulate a layer of condensed water, which will only be removed once the pipe is heated again. Once the pipe is heated again, water accumulated on the pipe outside will evaporate and most likely move in the form of vapour to be deposited as water droplets on the jacketing inside.

In case of a pipe steadily held at an elevated temperature, temperature variations may still arise due to varying circumstances in the environment, such as rain, wind, water spray and sunshine. Any such temperature variations are likely to cause transport of moisture with the risk of water condensing and being confined inside the insulation material. Although a steadily held elevated temperature is bound to reduce the relative humidity, it brings, on the other hand, necessarily also the disadvantage of an acceleration of the corrosion process. Therefore, even a comparatively small content of water inside the insulation material may be very harmful .

The publication PCT/DK95/00281 discloses a method of insulating a pipe, kept at a temperature below the temperature of the ambient air, by which method the pipe is covered with an insulating assembly, and a plug comprising capillary suction material is arranged to extend through the insulating assembly. This publication does not address the problem of removing moisture accumulated between a layer of heat insulation material and a protective jacketing.

The publication PCT/DK91/00132 discloses an insulation system for insulating cold conduits and containers, which system comprises an inner layer of a water absorbing material, a heat insulating layer, a diffusion proof layer, and an outer layer of a water absorbing material, wherein the layers of a water absorbing material are in mutual contact through openings in the other layers in order that water can be transported by capillary suction. The publication does not address the problem of removing moisture accumulated between the heat insulating layer and the diffusion proof layer.

It is the object of the invention to provide a thermally insulating cover structure for covering a heated body, which cover structure overcomes the above mentioned disadvantages associated with cover structures of the prior art.

This object is achieved with the cover structure as defined in claim 1.

In this cover structure, the heat insulation layer may comprise mineral wool, glass wool or any other heat insulation material known in the art. The filler layer may comprise a capillary active material or a more open material , e.g. a net or a granulate capable of forming a coherent net of voids, which will permit passage of liquids and gasses. With this cover structure any moisture gathered on the inside of the protection layer will be conveyed along the filler layer to a point, where it can be drained into the environment by dripping or by evaporation.

According to a preferred embodiment, the drain openings are covered by a water absorbing, capillary material, which allows passage of water while checking passage of air. This serves to reduce circulation of air inside the cover structure.

According to another preferred embodiment, the drain openings are shielded against entry of water by means of a lip, adapted for diverting any water flowing along the outside of the protection layer as well as any water impinging from the outside. This reduces the likelihood that water from the environment will find its way into the inside of the cover structure.

According to still another preferred embodiment, the heat insulation layer together with the filler layer are adapted for providing structural support to the protection layer. This permits the use of a comparatively light protective jacketing without compromising the requirement that the jacketing should be capable of enduring mild accidental loads, e.g. walking, without suffering disfiguring deformations.

It is a further object of the invention to provide a pipeline, which avoids the above mentioned problems associated with pipelines according to the prior art. This object is achieved with the pipeline as defined in claim 9.

It is a still further object of the invention to provide a method of providing a pipe with a thermally insulating cover structure, which avoids the problems associated with the methods according to the prior art.

This object is fulfilled with the method as defined in claim 13.

Still further objects, advantages and features of the invention will appear from the appended detailed description of preferred embodiments hereof, which is presented with reference to the drawings, whereon:

Fig. 1 shows a vertical, transverse section through a pipeline according to a first embodiment, and Fig. 2 shows a vertical, longitudinal section through a pipeline according to a second embodiment.

The drawings are schematic and not necessarily to scale, illustrating only features essential to enable those skilled in the art to understand and practice the invention, whereas other features have been omitted from the drawings for the sake of clarity. Throughout the drawings identical references are used to designate identical or similar features.

Reference is first made to Fig. 1, which illustrates a vertical, transverse section through a pipeline, which extends horizontally.

Fig. 1 illustrates a pipe 1 for conveying a heated fluid. The pipe is covered peripherally by a layer 2 of insulation material such as mineral wool. A web of water absorbing felt is wrapped around the layer of insulation material to provide a peripheral cover layer 3, with angled edge regions 4, extending radially away from the pipe.

A web of plate material is wrapped around the layer of felt in order to provide a peripheral, protective jacketing 6, with angled edge regions 7, extending radially away from the pipe with a narrow mutual spacing. The spaced edge regions define a slit 5, accommodating the protruding edges of the felt. The jacketing edge regions may be interconnected by rivets or the like (not shown) for reasons of simple securing of structural stability.

The width of the jacketing edge regions should preferably be sufficient to shield the radial portions of the felt against the impact of any droplets of water. In any case the jacketing edge regions should be so formed, that any water flowing along the jacketing outside will be diverted from any contact with the extended portions of the felt. These requirements will generally be fulfilled for all attitudes of pipe installations, except vertical pipes, if the jacketing edge regions extend radially at least equally far as the felt edge regions.

Reference is now made to Fig. 2 for an explanation of a second embodiment of the invention.

Fig. 2 illustrates a vertical pipeline in a longitudinal, i.e. axial section. This figure shows a pipe 11, covered by a layer of insulation material 12. A layer of felt 13 forms a hose, covering the layer of insulation material, while a protective jacketing 16 provides the peripheral finish of the structure. Fig. 2 further illustrates peripheral gaps formed in the two outermost layers, the respective upper edges portions of which have been flared outwardly, similarly to a socket, which receives the respective, upper edge portions of the adjacent parts below. This provides an annular slit 15 in the jacketing, delimited peripherally by a jacketing rim 17 and through which slit a rim 14 of the felt layer crosses the jacketing.

The jacketing rim should preferably be sized and formed so as to shield the felt rim against any impact of water, which requirement will generally be met for vertical or inclined pipes, if the jacketing generally covers the felt rim peripherally. In any case, the jacketing rim should be so formed, that any water flowing down along the jacketing outside will be diverted from any contact with protruding portions of the felt.

Preferred materials for the layer of insulation material comprise mineral wool, glass wool or other materials known in the art. A mineral wool of a density in the range from 20 to 200 kg/m^J has been found to perform well .

Preferred materials for the filler layer comprise non- woven felt of glass fibres, polyamide fibres, or other synthetic fibres. A layer of non woven glass fibre with a thickness in the range from 0.2 to 1.0 mm has been found to perform well. Other implementations of the filler layer comprise granular materials, wherein a capillary action is achieved by the surface contact between contacting granules, or the filler layer may comprise a wire net of steel or plastics, e.g. with a mesh size in the range from 1 mm to 20 mm. Still another implementation of the filler layer comprises a filling of small spheres, e.g. with diameters in the range from 10 mm to 20 mm. In this case, it may be practical to fit spacers or supports for maintaining the jacketing in the intended position.

The jacketing preferably comprises a plating of galvanized steel or aluminium to a thickness in the range from 0.1 to 1.0 mm. The plating may be flat or corrugated. Any joints in the jacketing should be made so as to generally prevent entry of water according to the circumstances expected at the site of installation.

Claims

PATENT CLAIMS

1. A thermally insulating cover structure adapted for covering the surface of a heated body, comprising

- a heat insulation layer of heat insulation material adapted for covering the body surface, said layer being delimited by an inner surface adapted for contacting the body surface, and by an outer surface, - a filler layer comprising a material permeable to liquids and gasses, which layer is delimited by an inner surface generally contacting the outer surface of the heat insulation layer, and by an outer surface, and

- a protection layer providing a generally water-tight barrier adapted for protecting the filler layer against the environment, said protection layer being provided with drain openings, shielded against entry of water and adapted to permit water in the filler layer to cross the protection layer to be discharged to the environment by dripping or by evaporation.

2. The cover structure according to claim 1, c h a r a c t e r i z e d in that the drain openings are covered by a water absorbing, capillary material, which serves to allow passage of water while checking passage of air.

3. The cover structure according to claim 1 or 2, c h a r a c t e r i z e d in that the drain openings are shielded against entry of water by means of a lip adapted for diverting any water flowing along the outside of the protection layer as well as any water impinging from the outside.

4. The cover structure according to any of the claims 1, 2 or 3 , c h a r a c t e r i z e d in that the heat insulation layer together with the filler layer are adapted for providing structural support to the protection layer.

5. The cover structure according to any of the claims 1- 4, c h a r a c t e r i z e d in that the filler layer comprises a water absorbing, capillary material.

6. The cover structure according to any of the claims 1- 5, c h a r a c t e r i z e d in that the filler layer comprises a non-woven felt.

7. The cover structure according to any of the claims 1-

6, c h a r a c t e r i z e d in that the filler layer comprises a net.

8. The cover structure according to any of the claims 1-

7, c h a r a c t e r i z e d in that the filler layer comprises a layer of loose, small bodies adapted for spacing the protection layer from the insulation layer while providing a net of coherent voids.

9. A pipeline adapted for carrying a heated fluid, said pipeline comprising - a pipe adapted for conveying the heated fluid,

- a heat insulation layer generally enclosing the pipe and comprising a heat insulation material,

- a filler layer generally enclosing the heat insulation layer and comprising a material permeable to liquids and gasses, and

- a jacketing generally enclosing the filler layer and forming a generally water tight barrier, adapted for protecting the filler layer against the environment, the jacketing being provided with drain openings to allow moisture from the filler layer to cross the jacketing to be discharged to the environment by dripping or by evaporation, and with shielding means adapted for shielding the drain openings against the entry of water.

10. A pipeline according to claim 9 and adapted for vertical installation, c h a r a c t e r i z e d in that the drain openings comprise a peripheral slit demarcated by an upper and a lower edge of the jacketing, and in that the shielding means is provided by angling the upper edge of the jacketing outwardly to form a rim which constitutes a drip nose.

11. A pipeline according to claim 9 and adapted for non- vertical installation, c h a r a c t e r i z e d in that the drain openings comprise an axially extending slit demarcated by edges of the jacketing.

12. The pipeline according to claim 11, c h a r a c t e r i z e d in that the edges of the jacketing are angled outwardly to form drip noses.

13. A method of providing a pipe with a thermally insulating cover structure, said method comprising the steps of

- providing the pipe with a layer of heat insulation material, said layer forming a hose, which generally encloses the pipe,

- providing the hose with a layer of a filler material, which is permeable to liquids and gasses, said layer generally enclosing said hose, - providing on the outside of said layer of filler material a generally water tight jacketing, adapted for protecting the filler material against the environment,

- providing drain openings in said jacketing adapted for allowing any moisture to cross the jacketing to be discharged to the environment by dripping or by evaporation, and - providing shielding means adapted for shielding the drain openings against the entry of water.