Pipe joints or couplings – With assembly means or feature – Molded joint facilitator
Patent
1987-06-01
1989-02-28
Arola, Dave W.
Pipe joints or couplings
With assembly means or feature
Molded joint facilitator
285 53, 285292, F16L 1302
Patent
active
048079103
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a sleeve joint for plastic-sheathed insulated pipes, particularly for a district heating system, said joint comprising a joint sleeve of plastic material covering the joint area and overlapping the ends of the sheaths of adjoining pipes that are connected to each other, the respective ends of the sleeve being secured and sealed to the overlapped pipe sheath by means of a fillet weld of plastic material, the pipe sheath and the sleeve and the weld preferably being of polyethylene.
The invention also relates to a method of producing such a sleeve joint.
BACKGROUND ART
Prefabricated plastic-sheathed pipes are commonly used in district heating systems. When a district heating pipeline is laid, prefabricated pipe lengths are connected to each other, whereafter the joint area is sealed so as to provide a permanent, insulated, watertight joint that can withstand the operating conditions and loads.
For small and medium diameter pipes, normally a standard sleeve joint is used for sealing the joint area. The sleeve bridges the two pipe sheath ends involved while overlapping said sheath ends. Mostly, the sleeve ends are sealed to the pipe sheaths by means of shrink-on gaiters.
However, when large diameter pipes and high mechanical stresses are involved, it has proved that the standard sleeve joint is not adequate, because the heat necessary for the shrinking process is difficult to apply in a proper way and the joints obtained have a tendency to crack and give leaks, thus leading to a damaged pipeline.
Instead, when large diameter pipes are involved, V butt welding of a joint sleeve has been used, the joint sleeve having the same outer diameter as the pipe sheath.
Also, a so-called "Swedish Joint" has been used. This is a sleeve joint wherein the overlapping sleeve ends are sealed to the underlying pipe sheath ends by means of intermediate heat welded material including electrical heating means and pressurizing means.
It has been proposed to seal the ends of the sleeve of a sleeve joint merely by melting together said ends and the outer layer of the adjoining pipe sheaths, the sleeve having an inner diameter corresponding to the outer diameter of the pipe sheath. The melting heat is supplied via a heating ring applied around the joint area. This method have proved not to be successful.
It has also been proposed, in general terms, that the sealing of the overlapping sleeve ends of a sleeve joint could be made by fillet welds, such welds then replacing the shrinkon gaiters. However, there have been no practical suggestions as to how the fillet welds should be made and no practical experiences of on-site use have been discussed.
OBJECTS OF THE INVENTION
One object of this invention is to provide an improved sleeve joint involving fillet welds which in particular can be used in connection with large dimensions pipes and where tough demands are to be met.
Another object of this invention is to provide a method of producing such an improved joint, the method being suitable for on-site use.
SUMMARY OF THE INVENTION
In accordance with the invention, these objects are achieved by the sleeve joint and the method for producing same having the features set forth in the accompanying claims.
Thus, according to a first important feature, the sleeve joint of the invention involves an over-sized sleeve such that the inner dimension of the overlapping sleeve is greater than the outer dimension of the overlapped pipe to thereby provide a well-defined annular gap therebetween. In order to center the pipe sheath and the sleeve relative each other, spacer means are provided in said gap at either end of the sleeve so as to keep each sleeve end portion and the overlapped pipe sheath at predetermined mutual distances relative to each other all the way around. In other words the gap distances will be entirely controlled.
In order to obtain a uniform and strong weld and joint, it has proved to be essential that the gap distances are constant and do not change during the welding process when t
REFERENCES:
patent: 1577090 (1926-03-01), Zander
patent: 1947998 (1934-02-01), Mazza
patent: 2646822 (1953-07-01), Ferguson
patent: 3675950 (1972-07-01), Beene
Arts Dirk
Johansson Goran
Arola Dave W.
Oy Uponor AB
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