Electric heating – Metal heating – Of cylinders
Reexamination Certificate
2001-05-04
2001-11-06
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
Of cylinders
C219S125110
Reexamination Certificate
active
06313426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for welding pipes together. More specifically the invention relates to arc-welding together pipe sections when laying pipelines underwater, especially at sea.
2. Description of the Related Art
When laying a pipeline at sea it is customary to weld, on a lay-barge, individual pipe sections to a pipe string (the pipe string leading towards the seabed). The welding process takes place on the lay-barge. The pipe sections may consist of a plurality of pipe lengths each welded together on the lay-barge to form the pipe sections when required.
The pipe-string, when being laid, is under great tension and weld joints must, of course, necessarily be sufficiently strong to withstand the high forces imposed on the weld joints. Each time a pipe is welded to another pipe extensive tests are made to ensure that the quality of the weld joint formed is sufficient. The strength of a weld joint depends upon various factors, one being the geometry of the path traced by the point of contact of the arc in relation to the surfaces of the pipes to be joined. If the point of contact of the arc is off target by as little as a tenth of a millimeter the quality of the joint may be reduced by enough that the pipe joint is rejected, when tested, as not being of sufficient quality. It is therefore important that the weld metal is laid down in the region of the joint with great accuracy.
Furthermore the radial distance of the electrode with respect to the pipes must change in relation to the depth of the weld joint. As the region of the joint between the pipes is filled with welded metal the surface of the welded metal gets closer to the welding torch.
There are therefore special considerations that must be taken into account when designing an apparatus for welding such pipes together.
A known method of welding two pipes together may be described as follows. The pipes to be joined are prepared prior to the welding process by bevelling the ends of the pipes such that when the pipes are arranged immediately before the welding process commences (coaxially with respect to each other), an exterior circumferential groove is defined between the two pipes. The pipes are positioned ready for welding. A carriage is mounted on one of the pipes for movement around the circumference of the pipes to be joined. A welding torch is mounted on the carriage and the apparatus is so arranged that the end of the metal electrode of the torch is opposite and relatively close to the circumferential groove. The carriage is moved around the circumference of the pipe and the torch is operated so that an arc is directed into the groove. The arc is guided manually and/or by various mechanical sensors to guide the arc as accurately as possible along the length of the groove. The welding process generally takes several passes. In the above-described method the resolution of the mechanical sensors is/such that a human operator is required to assist in the welding process for guiding the arc with sufficient accuracy.
The time it takes to lay a given length of pipeline is, to a great extent, determined by the time it takes to perform all the necessary welding operations. There is therefore a benefit in reducing the time it takes to weld two pipes together. Any attempt to speed up the welding process should not however lead to a significant reduction in the quality of the weld joint.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus and method for welding pipes together that mitigates at least some of the above-mentioned disadvantages associated with the known method and apparatus described above. A further object of the present invention is to provide an apparatus and method for welding pipes together that is faster at welding pipes together than the known method and apparatus described above but without significantly reducing the quality of weld joint.
According to the invention there is provided a welding apparatus for welding pipe sections together to form an underwater pipeline, the welding apparatus being arranged to weld pipe sections together when they are in a generally upright orientation with the bottom of an upper pipe section abutting the top of a lower pipe section that defines the end of the pipeline, the welding apparatus including:
a rotary equipment holder mounted for rotation about a generally vertical axis and having a central opening through which pipe sections are able to pass as a pipeline is laid,
a plurality of welding heads angularly spaced about the rotary equipment holder, each head being associated with a respective sector of the rotary equipment holder, and
a welding head guide assembly for fixing around a pipe section, the guide assembly including a guide track for guiding movement of each of the welding heads around the pipe section, the respective sector of the rotary equipment holder being able to revolve around the pipe section as the associated welding head revolves around the pipe section.
The invention makes it possible to operate a plurality of welding heads simultaneously around the pipeline thereby enabling the welding process to be speeded up considerably. At the same time the provision of the rotary equipment holder makes it possible to operate a plurality of welding heads without a risk of one welding head interfering with the operation of another.
Preferably the welding heads are arranged to be driven around the guide assembly. Such an assembly enables the path of movement of each welding head to be carefully controlled and also enables close control of the rotational speed of each welding head, enabling all heads to be rotated at the same speed.
In an embodiment of the invention described below with reference to the drawings, the welding head guide assembly is fixed around the pipe immediately below the joint to be welded (in that case, the assembly is fixed to the top of the pipeline); an alternative approach, which may sometimes be preferred, is to fix the assembly around the pipe immediately above the joint to be welded (in that case, the assembly is fixed to the bottom of the new pipe section being added to the pipeline).
The precise number of welding heads and their angular disposition around the pipeline can be chosen having regard to the needs of a particular application. Generally it will be preferable for at least two heads to be angularly spaced far apart from one another so that they can readily be operated without interfering with one another. The welding heads are preferably equiangularly spaced and in an embodiment of the invention described below three welding heads are provided. In other applications it may be preferable to employ two or four welding heads.
Preferably the gas and/or power supply equipment for each welding head is mounted on the respective sector of the rotary equipment holder with which the welding head is associated. In such a case the supply equipment is able to rotate on the rotary equipment holder in synchronism with the rotation of the welding heads around the pipeline. Preferably the connection of each welding head to its supply equipment is provided by a flexible umbilical connecting member. The flexible connecting member is able to compensate for any relative rotational movement between the welding head and its supply equipment (such rotational movement not being very great) and also to compensate for radial relative movement of the welding head and the supply equipment caused by the inclination of the pipeline. The supply equipment is preferably located around an outer region of the rotary equipment holder. The inner region above and or below the rotary equipment holder then remains free for an operator.
The apparatus is preferably arranged to be able to weld pipe sections together when they are in a generally upright orientation but at an inclination to the vertical and to the axis of rotation of the rotary equipment holder. Such a requirement is commonly required when using a “J-lay” technique of pipe laying.
Belloni Antonio
Bonasorte Renato
Burns Doane Swecker & Mathis L.L.P.
Saipem S.p.A.
Shaw Clifford C.
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