Induction heating apparatus and method for pipeline welding oper

Electric heating – Inductive heating – Metal working

Patent

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Details

219611, 219643, 219670, 219672, H05B 640

Patent

active

06166359&

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to the use of electrical induction heating in pipeline welding operations, particularly, but not exclusively, welding operations carried out underwater, as in the offshore oil industry.
Most particularly, the invention is applicable to welding operations of the type where a length of pipe is welded to an existing pipeline which is already in service transporting fluids, so as to form a T-junction with the existing pipeline, without interrupting the flow of fluid in the existing pipeline. In such cases, the new length of pipeline is welded to the exterior surface of the existing pipeline, prior to forming an aperture in the existing pipeline to enable fluid communication between the new and existing pipes. Such operations are referred to in the art as "hot tap interventions". The invention is primarily intended for use in relation to subsea pipelines.
It is common in many types of welding operation to pre-heat the workpieces in the vicinity of the weld zone by means of electrical resistance heating, so as to facilitate the welding process. In the case where the operation is of the "hot tap" type, the fluid flowing through the existing pipeline conducts thermal energy away from the weld zone, so that conventional resistance heating elements are unable to supply sufficient energy to pre-heat the workpieces to the required temperature.
Accordingly, it is common practice to utilise electrical induction heating techniques in order to increase the pre-heating energy which can be supplied to the workpieces. Such techniques generally involve the use of annular induction coils, in which the conductors of the coils extend around the circumference of the new pipe on the surface of the existing pipe in multiple turns, as illustrated in FIG. 1 of the accompanying drawings. The coils are supplied with medium frequency alternating current. The electromagnetic flux 10 generated by the coil 12 is coupled into the workpieces 14 (the new pipe length) and 16 (the existing pipe) as shown, generating eddy currents in the workpieces and thereby increasing their temperature. An insulating mat 18 separates the coil 12 from the existing pipe 16.
The arrangement shown in FIG. 1 has significant disadvantages. The coils themselves are inefficient, as much of the input electrical energy is wasted in heating the coil itself. Also, as can be seen from the drawing, a substantial proportion of the flux is coupled to the pipes 14 and 16 well away from the weld zone, which extends around the end of the new pipe 14. Besides being wasteful of energy, this also means that the body of the new pipe 14, which has no fluid flowing through it, becomes overheated. The co-axial arrangement of the new pipe 14 and the coil 12 increases such overheating.
A solution to the overheating of the new pipe length (hereinafter referred to as the "pipe stub") is proposed in GB-A-2214118. This solution involves the use of "shielding" which surrounds the pipe stub and which is movable along the pipe stub towards and away from the weld zone. In all of the embodiments disclosed, the "shielding" comprises an arrangement for circulating cooling fluid around the exterior surface of the pipe stub. Accordingly, this solution requires relatively complex, additional apparatus, and does nothing to avoid the dissipation of thermal energy away from the weld zone.
It is an object of the present invention to provide improved methods and apparatus for use in pre-heating workpieces in welding operations such as those involved in hot tap intervention procedures.
In accordance with a first aspect of the invention, there is provided induction heating apparatus for use in welding an end of a first length of pipe to the exterior surface of a second length of pipe, consisting of at least one heating assembly comprising at least one electrical induction coil wound on an annular, laminated, magnetic core assembly, the lowermost surfaces of said core assembly defining a saddle shape so as to be capable of being seated on the exterior surface of said second leng

REFERENCES:
patent: 4371768 (1983-02-01), Pozna
patent: 4590346 (1986-05-01), Sugihara et al.
patent: 4687894 (1987-08-01), Koga et al.
patent: 4694131 (1987-09-01), Ino et al.

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