Patent Application
20080178466
1. Field of the Invention
The present invention relates to pre-insulated piping systems, and more specifically to a method for manufacturing a length of pre-insulated piping of the type having an inner steel carrier pipe surrounded by an outer layer of insulating foam which, in turn, is surrounded by an outer waterproof plastic jacket, in order to ensure a more uniform bond between the layer of foam insulation and the outer waterproof plastic jacket.
2. Description of the Prior Art
There are many instances in which insulated pipelines are needed. For example, distributed HVAC (heating, ventilation and air conditioning) applications utilize chilled water for cooling and steam for heating. The chiller and boiler are typically contained in a central location and the chilled water and steam are distributed to other locations. For example, on a school campus, the chiller and boiler may be located in a power plant building. The chilled water and steam are distributed to classrooms in separate buildings.
A set of insulated pipelines is used to convey the chilled water from the chiller to other locations and back to the chiller. Another set of insulated pipelines is used to carry the steam from the boiler to the other locations and back to the boiler. The insulated pipelines are usually located underground.
Insulated pipe is conventional and commercially available. There are predominately two types of piping systems in use: Class-A drainable dryable testable (DDT); and polyurethane or polyisocyanurate “bonded” foam systems. Both of these systems use an inner carrier pipe to convey fluid. Although steel is commonly used for the inner pipe which carries the media to be piped, copper or aluminum or other metals as well as fiberglass, PVC, and similar materials may be utilized, as well. The present application is directed toward the “bonded” foam type system. These systems utilize a steel pipe to convey fluid. Around the outside of the steel pipe is a layer of insulating foam such as, for example, polyisocyanurate foam. The foam layer is, in turn, surrounded by a jacket of a hard thermoplastic material (such as high density polyethylene, HDPE).
As a part of the foam curing process, the foam sets up or hardens within the outer jacket so as to bond to both the outer jacket and to the inner fluid conveying pipe. The plastic jacket protects the foam from mechanical damage and also provides a water tight seal to prevent corrosion of the steel pipe. In the bonded type system, the foam and outer jacket are not intended to move relative to the inner pipe. In the Class-A type system, on the other hand, the insulated inner pipe is designed to move independently of the associated outer jacket. In fact, there is an air gap between the inner pie and outer carrier pipe in the class-A type system.
As a result of these differences in the two designs, one of the most important engineering criteria for the traditional “bonded” foam type system is that it must be treated as a monolithic system. In other words, the foam must be uniformly bonded to both the inner carrier pipe and the outer jacket. However, the slick interior surface of the HDPE outer jacket poses certain problems in achieving a completely uniform adhesive bond between the foam layer and the outer protective jacket. Even if the interior of the outer HDPE jacket is treated with an abrasive treatment such as sand blasting, in some cases the bonding is non-uniform over at least portions of the contact area.
This type of non-uniform bonding can create problems in certain circumstances. For example, sections of insulated piping are sometime left outside in the weather, either at the manufacturer's plant, or at a job site, until they are needed. Any section of jacket and foam that are not completely and uniformly bonded together will allow for the potential of water to migrate into the system. Normally, this amount of water should be small and the potential detriment that may cause to the system would be insignificant. However, there is always the possibility of the system being submersed under water for a prolonged period (rainstorms during installation when the pipe is in a trench, but not yet completely installed are a problem that causes this because the trench fills with water and the pip is submerged under water until the trench can be pumped out). In these types of situations there is increased potential of more significant water migrating between areas of non bonding between the jacket and foam.
Thus, despite the advances which have been made in foam bonding technologies, a need exists for improvements in manufacturing methods for pre-insulated piping systems which will ensure a more uniform bond between the layer of foam insulation and the outer waterproof plastic jacket.
The present invention provides a method of manufacturing a length of pre-insulated piping of the type having an inner steel carrier pipe surrounded by an outer layer of insulating foam and, in turn, an outer waterproof plastic jacket, in order to ensure a more uniform bond between the layer of foam insulation and the outer waterproof plastic jacket. The process begins with a cylindrical length of plastic (typically HDPE) jacket which has an exterior surface and an interior surface. The interior surface of the plastic jacket is flame treated in order to improve the adhesion qualities of the interior surface of the jacket. Next, an inner steel carrier pipe having an exterior and an initially open interior is provided. The inner steel carrier pipe is placed inside the plastic jacket to thereby create an annular space between the exterior surface of the steel carrier pipe and the interior surface of the plastic jacket. Lastly, foam insulation is injected within the annular space between the exterior surface of the steel carrier pipe and the interior surface of the plastic jacket. The foam fills the annular space and bonds with the inner steel carrier pipe and with the surrounding waterproof jacket.
The flame treatment of the interior of the plastic jacket can be performed in a number of different ways. For example, in one version of the method of the invention, the flame treatment is accomplished with a brush burner apparatus. A mounted brush flame apparatus is positioned within the interior of the cylindrical length of plastic jacket. The apparatus is mounted for movement longitudinally along the interior length of the jacket. Next, the brush flame apparatus is ignited and moved along the interior length of the jacket to thereby flame treat the interior surface of the plastic jacket. The flame treatment oxidizes the surface of the interior of the plastic jacket, thereby improving the adhesion properties of the jacket.
The brush flame apparatus can be constructed with a flame head having a plurality of flame openings which are directed toward an outer dispersion plate. The dispersion plate is positioned a selected distance from the flame head and positioned to deflect the associated flame radially outward toward the plastic jacket interior. In one form, the apparatus has a centralizer mechanism for centering the apparatus within the interior of the plastic jacket. For example, in one embodiment of the present invention, the centralizer is a plurality of spring legs mounted to the flame head.
Additional objects, features and advantages will be apparent in the written description which follows.
Turning first to
The reference in this discussion to pipe “lengths” is intended to refer to standard available factory pre-insulated piping of the type previously described having an inner metal pipe surrounded by an envelope of foamed insulation, which in turn, is contained within a polyolefin jacket. As referred to briefly above, typical commercial practice involves the use of steel, copper, aluminum or alloy conveying pipes, open or closed cell polyurethane, polyisocyanurate, polystyrene or the like, foamed rigid insulation and polypropylene, polybutylene, polyethylene, polyvinylchloride and similar protective jackets.
The present invention is an improvement to presently available pre-insulated piping of the type which is commercially available and familiar to those in the relevant industries. Prior art pipe lengths of this general type are commercially available as standard factory type product. For example, such product is available from Thermacor Process, LP of Fort Worth, Tex., assignee of the present invention. One typical example is sold commercially as the HT-406 High Temp Steel Piping System. The published specifications for systems are as follows:
The present invention has as its primary object to provide a method for manufacturing a length of pre-insulated piping of the type mentioned above, which method ensures a more uniform bond between the layer of foam insulation and the outer waterproof plastic jacket. As explained in the Background discussion, it is vital to the integrity of the pre-insulated piping system that a uniform bond be created between the insulating foam and the interior surface of the plastic jacket 13. The uniform bond keeps the system monolithic and also prevents undesired elements, such as moisture, to enter any air pockets or gaps between the foam and the plastic jacket, which could later result in damage to the piping system.
Turning now to
While such qualities as abrasion resistance are of value for the exterior of the jacket, the “slick” nature of the interior surface of the jacket presents a problem as far as the adhesion qualities of the material. The method of the invention aims to improve the adhesion qualities of the waterproof plastic jacket by a physical process which is relatively simple to implement and economical to practice.
In the first step of the method of the invention, the interior surface of the HDPE jacket is treated by exposing the surface to an open flame for a selected period of time. The resulting oxidation of the jacket interior surface has been found to remarkably improve the adhesion properties of the surface, thereby allowing a more uniform foam bonding in the subsequent steps of the method. In the particular embodiment of the invention illustrated in
Once the outer protective jacket 13 has been flame treated with the brush flame apparatus 61, a steel carrier pipe 11 is placed inside the plastic jacket 13, as shown in
The particular type of foam insulation utilized will depend upon the requirements of the particular end use for the piping system. For lower temperature application, a polyurethane foam insulation may be utilized. For higher temperature (steam) systems above about 250° F., the polyisocyanurate family of foams are preferred. Due to the “stickier” surface of the interior of the flame-treated plastic pipe, the insulating foam has been found to form a more uniform bond to the interior jacket surface.
An invention has been provided with several advantages. The method of the present invention improves the adhesion qualities of the interior of the outer protective jacket in order to ensure a uniform bonding of the insulating foam to the interior surface of the plastic jacket. The brush flame apparatus is constructed in such a way as to provide an even oxidation along the length of the jacket interior surface, while avoiding any damage to the surface being treated or reducing the functionality of the plastic jacket as a whole. The present system provides a more integrally sealed environment for the inner carrier pipe which resists the intrusion of water or other contaminants which could cause rust or corrosion. The flame brush apparatus which is utilized in the practice of the invention is simple in design and economical to manufacture and use. The method of the invention is therefore more economical to implement than more exotic treatments, such as corona treatment processes, and the like.
While the invention has been shown in one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.
