Stock material or miscellaneous articles – Hollow or container type article – Glass – ceramic – or sintered – fused – fired – or calcined metal...
Reexamination Certificate
2000-02-15
2003-10-21
Juska, Cheryl A. (Department: 1771)
Stock material or miscellaneous articles
Hollow or container type article
Glass, ceramic, or sintered, fused, fired, or calcined metal...
C428S035900, C428S036200, C428S036400, C428S036900, C428S036910, C138S140000, C138S149000, C138S151000, C138S152000, C138S156000, C138S163000
Reexamination Certificate
active
06635322
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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 jacket or sheathing adapted for protecting the heat insulation material against the ingress of water.
The invention further relates to a pipeline adapted for carrying a heated fluid. Further, the invention relates to a method of providing a pipe with a thermally insulating cover structure.
Heat insulation material generally 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. A jacket provides protection against ingress of water and against mechanical stresses. 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 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 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 pipeline subject to intermittent heating due to intermittent service in carrying of heated fluids. Varying temperatures in the structure may also arise in association with pipelines 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 jacket, air will be sucked from the surroundings and through openings in the jacket 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. 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. As the insulation material is not very permeable to water, at least in its undegraded state, it will tend to confine any droplets of condensed water to stay where they are.
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 vapor and air. Some air may leave the insulation structure, possibly carrying some vapor 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 jacket 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 vapor to be deposited as water droplets on the jacket 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.
2. Description of the Prior Art
U.S. Pat. No. 5,520,009 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 jacket.
Applicant's U.S. Pat. No. 5,441,083 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.
SUMMARY OF THE INVENTION
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.
In a first aspect of the invention, this object is provided by a thermally insulating cover structure adapted for covering a surface of a heated body, comprising a heat insulation layer of a heat insulation material adapt ed 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 said heat insulation layer, and by an outer surface, and a protection layer providing a generally water-tight barrier adapted for protecting said filler layer against the environment, said protection layer being provided with transverse drain openings, and shield means for shielding said drain openings against entry of water while permitting water in said filler layer to cross said protection layer to be discharged to the environment by dripping or by evaporation.
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 granulates 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 draine
Hygrowick-International Aps
Juska Cheryl A.
Vigil Thomas R.
Welsh & Katz Ltd.
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