Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1998-07-31
2000-12-26
Maki, Steven D.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
138 99, 156 98, B05D 132, B05D 108, B29C 6306, F16L 5810
Patent
active
061653020
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns a process for repairing plastic coatings of metal pipes, that allows the repairs to be made in a very short time.
Metal pipes, usually made of steel, coated with plastic material, are widely used for building pipelines conveying fluid materials, such as oil, natural gas, or water, even for a long distance.
Said pipelines must be able to withstand the most diverse environmental conditions, and, in certain cases, the high temperatures that are maintained in the proximity of pumping stations, for example, or that may be typical of certain fluids extracted from the subsoil.
In order to avoid weak points along the line it is necessary, therefore, that the damaged or removed segments of the plastic coating (where the pipes are welded together, for example) be repaired in such a way that the mechanical properties are as homogeneous as possible with the ones of the original coating.
As a response to said needs there are materials and methods known in the art which allow one to reach said objective with satisfactory results.
However, when the damaged portion of the coatings is quite extensive (for example when the coating has been removed in order to weld the pipes), one needs complicated repairing techniques requiring long times, and sophisticated and costly apparatus, such as induction ovens.
Now has been perfected a particularly fast and efficient repair method which allows one to limit the use of the induction oven to the heating phase preceding the application of the primer, and to carry out the other heating phases by using a flame shielded by inert gas (such as nitrogen, for example).
Said process is particularly suited for repairing polyolefin coatings, preferably polypropylene and/or polyethylene coatings.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is a process for repairing coatings on metal pipes the coatings being made of plastic materials (in particular polyolefin, preferably polypropylene and/or polyethylene coatings), the process comprising the following operating phases: substances) of the exposed portion of the metal pipe (i.e., the one without coating), example) on the edges of the existing coating surrounding the exposed portion, induction ovens) to a temperature ranging from 140 to 270.degree. C., preferably from 170 to 240.degree. C., and a polyolefin adhesive in powder form, of a polyolefin tape, by way of wrapping and heating the tape with an inert gas-shielded flame.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Preferably, the size of the shells used in phase 2) is such that they overlap the existing coating by about 10 centimeters from the edges.
Said shells serve the purpose of preventing the coating from splitting and lifting during the heating of phase 3).
In phase 4), the epoxy primer in powder form and the polyolefin adhesive in powder form are preferably applied by using guns that are fed from a fluid bed by way of a pump which aspirates the powders using the Venturi effect.
Said guns can be equipped with a system for the electrostatic charge of the powders.
Various alternative solutions are possible for phase 5). In particular phase 5) may comprise the following steps: coating by way of an inert gas-shielded flame, coating by way of flame spraying, polypropylene and/or polyethylene tape) having preferably a thickness of 800 microns, on the exposed portion and on the surrounding area of the existing coating, preferably overlapping the edges of the tape being wrapped by 50-70% of its width, optionally,
In step 5iv), the area of the existing coating, surrounding the exposed portion, which is covered with the tape consists preferably of at least 1.5-2 turns of said tape at both sides of the pipe surrounding said exposed portion.
As an alternative, phase 5) may comprise the following steps: polyolefin adhesive in powder form (in the case that one would want to increase the thickness of the coating), polypropylene and/or polyethylene tape) on the exposed portion and on the shells made of rigid m
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patent: 6029710 (2000-02-01), Rigosi et al.
Marzola Roberto
Rigosi Gian Luigi
Maki Steven D.
Montell North America Inc.
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