Pipe joints or couplings – Molded joint – Lining or cover molded to pipe end
Patent
1994-12-08
1995-11-07
Reese, Randolph A.
Pipe joints or couplings
Molded joint
Lining or cover molded to pipe end
285381, 285417, F16L 4700, F16L 2506
Patent
active
054642582
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Testing of welded joints in, for example, pressure vessels or tubes often leads to different types of fault indications in the weld or in material adjoining the weld. This has become accentuated by the introduction, especially in nuclear power plants, of new testing technique and new testing criteria. It is known in, for example, straight rotationally symmetrical tubes to place a compression joint over the welded joint to reinforce this and prevent crack growth in the region around the weld. For this purpose, compression joints consisting of a winding in several layers of strip or wire have been used. The strip or wire has been of memory metal. Prior to being wound on, with no significant tensile stress in the wire around the tube, at a temperature below the transition temperature of the memory metal, the wire has been stretched to a suitable length to achieve the desired compressive stress in the joint after the winding around the tube and a subsequent increase of the temperature above the transition temperature.
If the joint weld is arranged between a straight and a bent tube or between two bent tubes, however, difficulties arise in winding on a strip or a wire around the joint since the bent tube does not form a rotationally symmetrical base for the winding operation.
SUMMARY OF THE INVENTION
The present invention relates to an invention which eliminates the above-mentioned difficulties. According to the invention, the compression joint comprises a first sleeve whose inner surface is formed to fit closely around the tube over the point which is to be reinforced, for example a welded joint. The sleeve is divided into at least two parts along axial sections. The first sleeve is formed with an outer, substantially rotationally symmetrical surface. A second sleeve with a corresponding inner rotationally symmetrical surface is divided into at least two parts along axial sections and intended to be rotatably arranged around the first sleeve after the first sleeve has been placed around the reinforcement point. The outer surface of the second sleeve is designed to receive a winding comprising several layers of strip or wire of memory metal. Prior to being wound around the second sleeve at a temperature below the transition temperature of the memory metal, this strip or wire has been stretched to a suitable length to bring about the desired compressive stress in the joint after the winding around the second sleeve and a subsequent increase of the temperature of the winding above the transition temperature.
Since the first sleeve has an external shape which is substantially rotationally symmetrical, the second sleeve can be given a corresponding rotationally symmetrical shape. This second sleeve can be caused to rotate around the first sleeve, whereby the strip or wire of memory metal is wound onto the second sleeve.
In order for the first sleeve to be placed around the bend, the sleeve has to be divided into at least two parts--preferably more than two--by means of axial sections. In that case, when the sleeve parts are applied around the bend, a certain minimum gap should be provided between the sleeve parts such that these can be pressed hard against the tube, by the second sleeve and the winding, when the temperature is raised above the transition temperature of the winding. Also the second sleeve must be divided into at least two parts to be able to be applied around the first sleeve. Also between these sleeve parts there should be a certain gap when they are mounted around the first sleeve.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be most readily understood with reference to FIGS. 1 and 2. FIG. 1 shows the first sleeve applied to the bend and FIG. 2 a section through a compression joint with the second sleeve mounted around the first sleeve.
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, 1 designates the tube bend, which in this case consists of a bent tube part 2 and a straight tube part 3 which are joined by means of a joint 4. Around this joint, cracks
REFERENCES:
patent: 4296955 (1981-10-01), Martin
patent: 4310183 (1982-01-01), Szalvay
patent: 4424411 (1984-01-01), Clabburn
patent: 4709948 (1987-12-01), Archer et al.
patent: 4836586 (1989-06-01), Martin
patent: 5169176 (1992-12-01), Brossard
patent: 5338070 (1994-08-01), Horikawa et al.
Kornfeldt Hans
Kornvik Lars-Ake
Tornblom Lars
ABB Atom AB
Chun Shackelford Heather
Reese Randolph A.
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