Work holders – Holder inserted within work aperture – Expandable mandrel
Reexamination Certificate
2000-04-28
2002-08-20
Watson, Robert C. (Department: 3723)
Work holders
Holder inserted within work aperture
Expandable mandrel
C228S049300
Reexamination Certificate
active
06435495
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a back-up clamp component for use in a back-up clamp for the welding of pipelines.
BACKGROUND TO THE INVENTION
Pipelines are in widespread use for the transportation of fluids such as water, gas and oil. Many such pipelines are of metal and are manufactured in lengths which must be assembled on site into the complete pipeline. To connect two adjacent lengths of pipe together it is usual to provide a welded joint. Thus, a new length of pipe is placed close to the end of the existing pipeline and a welded joint is formed therebetween (it is usual for a small gap to be present between the adjacent pipe ends prior to welding, which gap is filled by the weld). A subsequent length of pipe is then placed against the new end of the (extended) pipelipe, and the procedure is repeated.
To ensure an accurate and effective weld it is necessary that the two adjacent pipe ends be maintained in alignment during welding. In addition, a known concern with such welded joints is that weld material can be spattered through the gap and into the interior of the pipe, and can impair the subsequent flow of fluid therealong. It is therefore known to insert a back-up clamp into the pipeline adjacent the joint to be welded, the clamp serving to align the two pipe ends and also having a number of shoes which can be moved to lie beneath the gap and prevent any weld spatter from entering into the pipeline. Copper has been found to be a preferred material for the shoes, and in particular copper “101”.
DESCRIPTION OF THE PRIOR ART
A back-up clamp of the type described is disclosed in WO 95/21721. The back-up clamp comprises two sets of clamping members which are adapted to engage the respective pipes adjacent their ends and to assist the alignment of the pipe ends. Between the clamping members is a ring of copper shoes which is adapted to lie underneath the gap during welding. The clamping members and the copper shoes are movable between a retracted condition in which the back-up clamp can be moved along the pipeline, and an extended condition in which the clamping members and the copper shoes engage the inside surface of the respective pipes, the copper shoes lying immediately beneath the gap. The clamping members are moved inwardly and outwardly by a toggle mechanism actuated by pneumatic means. The copper shoes are urged into their extended condition by springs, and into their retracted condition by hooks carried by the clamping shoes.
It is a recognised disadvantage of the known device that it can only be used for larger diameter pipelines, i.e. those of around 8 inches (20.3 cm) diameter or greater, the size of the mechanical toggle linkages effectively providing the lower limit to the size of the device and thus the pipelines upon which the device can be used.
In addition, it is known that debris or other matter within the pipeline adjacent the gap can cause a copper shoe to fail to make contact with the wall of the pipe, so that weld spatter can subseqently enter the pipeline adjacent that shoe. Thus, since it is only the relatively weak spring force that is urging the copper shoes into contact with the pipeline this force cannot overcome certain debris in the path of the shoe.
Furthermore, because the clamping members are required to ensure the alignment of the pipe ends they are necessarily located close together (so that each can be located close to the end of its respective pipe). The need to locate the clamping members close together significantly limits the design freedom for the copper shoes (which lie between the clamping members). In addition, since the clamping shoes are located close to the ends of their respective pipes, whilst they can seek to ensure that the ends of the pipes are substantially concentric, they cannot necessarily ensure complete alignment of the pipes, since the longitudinal axes of the pipes may not be parallel. If the longitudinal axes of the pipes are not parallel the size of the gap will vary around the circumference of the pipeline, so that the effectiveness and reliability of the weld may be impaired.
Also, since the clamping members are not located at the very ends of the respective pipes, some misalignment (i.e. a lack of concentricity of the pipe ends) may be present, which misalignment can cause discontinuities or lips internally of the pipeline; clearly the presence of such discontinuities is likely to cause vortices and thus pressure drops along the pipeline (which pressure drops can accumulate and become considerable in a long pipeline).
GB Patent Application 2,067,945 also discloses a back-up clamp of the general type described. In this design also, the back-up shoes are urged into contact with the pipeline by spring force alone, so that the disadvantages of such an arrangement outlined above are shared by the devices of this disclosure. The back-up shoes are located adjacent (and indeed are carried by) the clamping members, and so the device is less well able to correctly align the longitudinal axes of the pipes which are to be welded.
U.S. Patent 5,110,031 discloses a back-up clamp in which the back-up shoes are of a ceramic material. In this document the clamping members and the back-up shoes are moved radially by respective radially acting pistons. It is indicated that the pistons are actuated by pneumatic or hydraulic means. No means is disclosed for the retraction of the clamping members or the back-up shoes.
GB Patent 1,528,775 discloses a back-up clamp in which the clamping members are actuated by way of a toggle mechanism, i.e. a piston is moved longitudinally by hydraulic or pneumatic pressure, and the longitudinal movement is converted to radial movement of the clamping members by mechanical links. The back-up shoes are however moved radially by radially acting piston and cylinder arrangements. Hydraulic or pneumatic pressure can be fed to both sides of the piston to effect forced extension and retraction of the back-up shoes.
Utilising hydraulic or pneumatic pressure to drive out the back-up shoes avoids the disadvantages outlines above for those disclosures relying upon spring force alone. The most significant advantage is that the force which can be exerted upon the pipeline (or rather the ends of the adjacent pipes which are to be welded together) is much increased, allowing the back-up shoes to contribute to the alignment of the pipes. This in turn permits the clamping members to be spaced further from the ends of the respective pipes than would otherwise be possible, increasing the likelihood that the longitudinal axes of the pipes are aligned.
There is also a significant advantage in driving the back-up shoes both outwardly and inwardly, i.e. rather than relying upon spring force to achieve the inward retraction movement, for example. Thus, when the back-up shoes are positively driven inwardly by hydraulic or pneumatic pressure there is far less likelihood of the back-up shoes “sticking” in their extended condition. Should the back-up shoes stick in their extended condition it would be difficult or perhaps impossible to move the clamp along the pipeline.
Notwithstanding the advantages of the device as disclosed in U.K. Patent 1,528,775, it is not in widespread use; and this is believed to be because of the complexity of the device. Thus, the device is mechanically complex, and also requires complex and numerous hydraulic and/or pneumatic connections to be made to communicate the pressurised fluid to the sites upon the clamp at which it is required.
In addition, the pressurised fluid is fed to the cylinder housing the piston of the back-up shoe by way of hoses connected to the clamp body immediately beneath the back-up shoe. With clamps for larger-diameter pipelines there is usually enough space to accommodate the hoses and permit access to the hose connections, but this becomes increasingly difficult to achieve as the diameter of the pipeline, and thus the diameter of the clamp, becomes smaller.
In addition, the hoses pass around a part of the clamp body, and are therefore susceptible to dama
Drewnicki Zdzislaw Leon
Eastham John Simon
Radbourne Kevin Alan
Vickery Keith
Pedersen Barbara S.
Pedersen Ken J.
Watson Robert C.
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