Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Direct application of fluid pressure
Reexamination Certificate
1999-05-27
2001-05-08
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Direct application of fluid pressure
C264S493000, C264S036160, C264S036170, C264S516000, C264S269000, C156S287000, C156S294000
Reexamination Certificate
active
06228312
ABSTRACT:
This invention relates to the manufacture and use of products fabricated from fibre reinforced thermoplastics composite materials. In particular the invention relates to methods of lining pipework and other ducts with such materials, and to the fabrication of duct liners and pipes from such materials.
Within the term “duct”, where it is used herein, is included pipes, tubes and conduits, whether for conveying fluids (e.g. a sewer) or for other purposes.
A variety of different techniques are currently in use for rehabilitating existing pipe systems by lining the existing pipework rather than removing and replacing it. Lining existing pipework is generally cheaper, and causes less disruption, than complete replacement programs and is thus widely used in the water and gas supply industries.
For instance, the majority of water mains in the UK are cast iron (most having a diameter of 150 mm or less). Failure of such pipework due to corrosion (both internal and external) is becoming an increasing problem as existing systems age. It is, for example, estimated that over 50% of all water mains in the UK have been in service for more than forty years and that 20% have been in service for more than eighty years. There is therefore an increasing demand for the development of effective rehabilitation techniques.
Conventional methods for lining pipework include cement and epoxy resin spray coating processes, and “slip lining” processes. The latter involves inserting a pipe liner, typically fabricated from polyethylene or PVC, into the existing pipework.
Slip lining is carried out in a variety of ways using a variety of different forms of pipe liner. For instance, one type of slip lining widely used in the gas industry, referred to as “swage lining”, involves winching an MDPE pipe liner into an in situ pipe having first pulled the liner through a die to reduce its diameter. Once in position the liner will expand and attempt to revert to its original diameter. Thus, after a period of twelve hours or so the liner will expand into a close fit within the host pipe.
An advantage of swage lining, and indeed other slip lining process, is that the liner can provide structural strength to the host pipe to meet requirements of high supply pressures. However, where such structural liners are used, steps must be taken to reduce the diameter of the liner so that it can be drawn into the pipe if a close fit between the liner and the pipe wall is to be obtained. Winch loads used can be very high which can provide an installation hazard. Furthermore, even with “close fit” slip lining techniques, such as swage lining, the liner may not properly revert to a close fit within the host pipe along its entire length if there are variations in the diameter of the pipe. This can result in gaps being left between the liner and the pipe wall which is undesirable. For instance, if the liner fails, fluid may run between the liner and the pipe wall before escaping and thus the externally observable manifestation of a leak or burst in the lining could be a considerable distance from the actual point of failure, making it difficult to identify the location of the failure.
It is an object of the present invention to provide a new method for lining pipework or other form of duct.
According to a first aspect of the present invention there is provided a method of lining a duct comprising:
inserting into the duct a liner comprising composite material comprising filaments of thermoplastic and filaments of reinforcing fibre;
heating the liner to melt the thermoplastic filaments;
applying pressure to the heated liner to press it into contact with the duct; and
enabling or permitting the liner to cool whilst in contact with the duct in order to harden the thermoplastic/reinforcing fibre composite.
A suitable composite material is available from Vetrotex International of 767 quai des Allobroges—BP 929, 73009 Chambery Cedex, France (a subsidiary to St. Gobain) under the registered trade name TWINTEX. TWINTEX is, for instance, available as wound rovings, or woven fabrics, or tows comprising homogeneously intermingled long filaments of thermoplastics such as polypropylene, polyethylene, polyethyleneterephthlate (PET) and polybutylterephthlate (PBT) with E-glass, the glass fibre content typically being 45 to 75 WT % (20 to 50 vol %). The TWINTEX manufacturing process enables the thermoplastic and glass fibre filaments to be mixed “dry” with a high degree of control over the distribution of the two filamentary fibres.
Consolidation of the TWINTEX “prepreg” material into a rigid composite is achieved by heating the material under pressure to melt the thermoplastic and disperse it amongst the glass fibres. Cooling the material then solidifies the thermoplastic which forms a solid matrix around the reinforcing glass fibres.
The homogeneous distribution of the filaments in the TWINTEX product ensures favourable processing conditions of temperature verses pressure and the resultant consolidated composite material has good mechanical properties. Further details of the TWINTEX product are readily available from the manufacturer.
Before consolidation, the composite material is relatively flexible and thus may be inserted into a duct to be lined whilst in a collapsed configuration and subsequently expanded to contact the duct wall.
During the installation process, pressure may be applied to the liner material to consolidate the composite during the heating stage and/or in between the heating stage and the cooling stage and/or during the cooling stage.
A variety of different methods may be used to heat the liner, including irradiating the liner with infrared radiation, or heating the liner using hot gas or steam.
It is preferred that in the duct lining method according to the present invention a liner comprising glass reinforcing fibres is used (e.g. TWINTEX), and infrared radiation is used to heat the liner. It has been found that glass fibres are particularly responsive/absorbent to shortwave infrared radiation (i.e. wavelength less than 2 &mgr;m) in particular frequency ranges. The glass fibres thus heat up relatively quickly and melt the thermoplastic filaments intermingled therewith, with relatively little heat loss to the surroundings. This is particularly advantageous when the method is used to line thermally conductive pipes such as cast iron water mains.
As a further means of limiting heat loss from the liner to the duct and surroundings, the liner can be provided with an external layer of insulating plastics material, for instance a thermoplastics material such as is used in the composite.
The liner may similarly be provided with an internal layer of plastics material, such as polypropylene or polyethylene, which provides the liner with an internal surface meeting accepted standards for transmission of, for example, potable water supplies.
Duct lining methods in accordance with the present invention are not limited to lining in-situ, but could be applied to the lining of new pipes at the place of manufacture. Similarly, methods according to the present invention are not restricted to the provision of internal pipe linings, but may be adapted to provide external pipe covers.
In another of its aspects the invention provides a method of applying a lining or cover, respectively, to an interior or exterior surface of a duct comprising:
applying a liner/cover to the duct which comprises composite material comprising filaments of thermoplastic and filaments of reinforcing fibre;
heating the composite material to melt the thermoplastic filaments;
applying pressure to the liner/cover to press it into contact with the interior/exterior surface of the duct; and
enabling or permitting the liner/cover to cool whilst in contact with the duct in order to harden the thermoplastic/reinforcing fibre composite.
Moreover, the present invention is not limited to the provision of pipe liners and the lining of pipes. In another of its aspects the invention provides a method of manufacturing a product, comprising knitting, braiding or weaving a composite mater
Schweitzer Cornman Gross & Bondell LLP
Severn Trent Water Limited
Vargot Mathieu D.
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