Pipelines laid on the sea-bottom normally are jointed above the water surface on special laying vessels as the pipeline is being laid.

In certain cases, however, for example when pipelines laid from different vessels are to be jointed, in the vicinity of platforms etc., the jointing operation must be carried out underwater on the sea-bottom.

At one known method a special jointing rig is lowered from a vessel. The rig is provided with means for handling and fixing the pipe ends and with a habitat, which is mounted over the place of jointing. The water about the joint can be removed by means of sealings within the pipes and about the same at their entrance into the habitat. The technical staff working in the habitat can hereby dry-weld the joints.

This process requires a highly qualified staff in respect of both diving and welding.

It takes two workers about 16 hours to carry out such a jointing operation. In the case of great depths, besides, the work cannot be carried out in one stretch by the same workers during such a long diving time, but the workers have to be exchanged. The expenditures, therefore, are very high.

Pipelines can be jointed by different known methods of explosive welding, on land as well as underwater. No known type of underwater joint, however, heretofore has been carried out so as to be approved by the checking authorities or so as to t>e economically acceptable.

The present invention proposes a method of underwater explosive welding, at which the deficiencies of convent¬ ional methods have ..been eliminated by various measures. Substantial economic advantages have been achieved by radically reducing the necessary diving time, and a considerable safety gain against leakage has been made by the combination of welded and mechanical weld.

The handling of the pipe ends always requires a jointing ^" rig with cranes for lifting the pipes and moving them into a position suitable for their jointing. When pipelines are to be jointed or repaired on the sea-bottom, the pipe lengths to be handled usually are very long.

It is, therefore, difficult and in many cases impossible to move the pipes in axial direction so as to accurately fit each other. After the habitat has been positioned, ^* and the pipes are sealed against the same, axial movement is not possible at all, because this would give rise to leakage.

According to the invention^ however, a jointing piece of a definite length is used, which prior to the explosive welding is dimensioned so that it can be threaded on the outside of one pipe end before the pipe is fixed in the rig. When the pipe ends have been fixed so that the central axes of the pipe ends align, the pipes are cross-cut so that a predetermined distance between them is obtained, which is adjusted to the jointing pipe. The said distance is such that the pipe ends only partially project into the jointing piece which, thus, constitutes a connecting pipe between the two pipe ends. Sealings, for example in the form of inflatable bags of plastic or rubber are inserted into each pipe end. The pipe ends, which can be

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cut straight or with bevel edge, are ground outwardly about the circumference in a zone of about 100 mm width nearest to the edges. These zones form joint surfaces at the explosive welding and, therefore, must be ground to a surface quality of Ra = 2.5 um. The explosive charges to be used at the welding are entirely encased and provided with an ignition system so designed that the charges are initiated simultaneously about their inner circum¬ ference. This is necessary for obtaining a seal weld all about.

The invention is characterized in that two identical explosive charges are used, which are positioned within the respective pipe end and connected to an ignition system causing the two charges to detonate accurately at the same time.

When both explosive charges have been positioned, the jointing pipe is moved so as to overlap both pipe ends. When the work is carried out in a habitat of a size sufficient for the workers to stay therein, the sealing and the removal of water in the habitat and pipe ends advantageously is effected so that all operations from cutting-off and grinding can take place in dry environment, which facilitates the work and also renders possible complete control of the joint surfaces to be-free from dirt and water. According to a preferred embodiment, when the jointing or repair work is carried out under¬ water in a habitat, the pipes are sealed against the jointing piece, and the pipes are sealed internally at the pipe ends. Thereafter the water is removed from the joint surfaces to be explosive welded, in that the water is pumped out in the volume enclosing the jointing piece. The impulse to trigger the detonation must be transferred to the detonating cap within the jointing pipe. It is in principle per se possible to lay out thin insulation- -painted conduit wires between the pipe ends and jointing

pipe without jeopardizing the quality of the joint. It Is safer, however, to transfer the impulse through the wall of the jointing piece inductively or by means of a shock wave.

At the triggering of the explosive charges, the pipe ends are flung outward to the jointing piece and explosive welded thereon. The diameter of the pipe ends, thus, is widened so that the pipe ends are flanged out to abut the inner surface of the jointing piece and are welded thereon. ear the respective end of the jointing piece.

The workers must be outside the habitat. At the detonation, the sealings in the pipe are destroyed. The habitat, however, is not filled with water, because the pipe then is sealed due to the two pipe ends having been welded on and jointed with the jointing pipe.

The weld joints now can be subjected to ultrasonic weld testing from the outside of the jointing pipe. It is obvious, that the same jointing method and process advant¬ ageously can be utilized above water, on board of ships or on land, in which case, of course, sealings within the pipe ends and the habitat are not required.

It is also possible to carry out the jointing operation without habitat, when sealings are applied within the pipe, and the outer rig after having been positioned is sealed at both ends and provided with supply conduits and drainage conduits for removing the water.

Fig. 1 shows schematically two pipe ends and an intermedi jointing piece. Pig. 2 shows an alternative embodiment of the prospective joint surfaces of two pipe ends and intermediate jointing piece.

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In the Figures, 1 designates the jointing pipe, 2 the explosive charges, 3 the pipe ends and 4 the ignition system.

In Fig. 1 the pipe ends are shown to have bevelled surfaces 5, which are to be explosive welded against the inner surface of the jointing piece at 6.

In Fig. 2, in addition to bevelled pipe ends 5 also angular joint surfaces 7 of the jointing piece are shown, with which the bevelled adges 5 are intended to be jointed at the detonation.

According to a preferred embodiment, the jointing pipe is supported at the explosive welding by a fixture located on the outside.

As appears from Figs. 1 and 2, the jointing piece is provided with flanges 8 at the ends. The inner diameter of the flanges must slightly exceed the out'er diameter of the pipe ends. The jointing piece portion 9 located between said flanges 8 has a diameter exceeding that of the flanges 8 in order thereby to effect the pipe ends to be flanged out in the way described above at the detonation.

According to the invention, thus, both an explosion jointing and a mechanic jointing between pipe ends and jointing piece are effected, which is particularly advantageous in respect of the sealing and the strength resulting therefrom. ,

Although the jointing piece, even with advantage, can be permitted to assume a certain deformation at the explosive welding, because then also a certain mechan- ical joint is obtained, the dimension and material, of course, must be calculated so that no fracture occurs.

Alternatively, an outer fixture can be applied which can be used repeatedly .

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