Pipes and tubular conduits – Distinct layers – Bonded to each other
Patent
1997-10-22
2000-01-25
Morris, Lesley D.
Pipes and tubular conduits
Distinct layers
Bonded to each other
138137, 264108, 428 3691, F16L 1104, F16L 1100, B29C 4724
Patent
active
060168498
DESCRIPTION:
BRIEF SUMMARY
This invention relates to plastics pipes and more particularly to a novel construction of plastics pipe, a method for its manufacture, and a method for making joints in such a pipe.
In the handling, installation and connection of plastics pipes, the pipe surface is easily damaged. In modern plastic pipe installation techniques, for example, a tunnel is bored in the ground for the pipe, and the pipe is then pushed or pulled through the tunnel, for example, into an excavated hole where the next pipe joint is to be made.
The pipe-laying method can subject the pipe to substantial bending, tensile and abrasive contact forces. This is disadvantageous since bending, stretching and abrasion of a pipe can result in a deterioration of its mechanical strength. In addition, the useful life of the pipe may be reduced by diffusible materials in the ground, or by environmental conditions.
It will be apparent that the method of pipe-laying can also result in the pipe becoming scratched and dirty. This is disadvantageous firstly as the pipe material may be notch sensitive, in which case any scratches may cause greater damage to occur in the pipe during subsequent handling or use. Secondly, dirt on the pipe prevents successful welding. At the present time, a common technique for jointing plastic pipes is electric welding, and particularly electrofusion welding, using an electrofusion coupler. The main reason for failure of joints using an electrofusion coupler is that the surface of the pipe is dirty or has become oxidised. For this reason the pipe ends always have to be cleaned and abraded or scraped, for example with sandpaper or a metal scraper, before jointing. In practice, the cleaning and abrading or scraping is often uneven (the underside of the pipe in particular may be treated less carefully) and the quality of the end result depends upon the professional skill of the installer.
A variety of suggestions have been put forward to overcome the above-mentioned disadvantages.
In European Patent Application No. 0474583 there is described a plastic pipe to be laid in the ground which comprises a gas or water conducting core pipe provided with an outer hose of a thermoplastic material having a higher flexibility than the material of the core pipe. The pipe is stated to be able to resist the extensive mechanical stresses to which it is subjected during direct laying into the ground. It is stated to be easy to remove the outer hose adjacent the ends of the pipe when two pipe sections are to be assembled by welding. It is also stated that formation of cracks caused by damage to the protective hose does not spread to the core pipe, but stops when the hose has been penetrated.
In PCT/FI92/00201 there is described a plastics pipe for making pipe joints characterised in that the pipe is covered by a plastic surface layer as a protective coating which is easily detachable at least at the ends of the pipe, in order to uncover the joint surface of the pipe necessary for making the pipe joint. The protective coating can contain UV stabilisers and may be applied by co-extrusion through a cross-head extrusion nozzle. Various ways of making the protective coating easily detachable from the core pipe are disclosed, including the use of fillers in the coating, the choice of chemically different plastics materials for the coating and the pipe, extruding the coating at low temperatures, and the introduction of adhesion preventing agents.
In PCT/FI93/00038 there is described a two-layer plastics pipe which comprises a core pipe whose material, size and structure essentially meet the requirements set by the material to be conveyed and an outer hose provided around the core pipe by a suitable coating method, the properties of the outer hose essentially meeting the requirements set by the environment and for the laying procedure. The stiffness of the outer hose, based on its material properties or the design of the outer hose, is higher than the stiffness of the core pipe manufactured from the same amount of material, and the outer hose is remo
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Andersson Mikael
Harget David Charles
Holso Eino Matias
Jarvenkyla Jyri Jaakko
Hwu Davis
Morris Lesley D.
Uponor Limited
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