Metal fusion bonding – Process – Using explosive energy
Patent
1984-10-30
1989-03-28
Rowan, Kurt
Metal fusion bonding
Process
Using explosive energy
228108, 228109, B23P 309, B23K 2008
Patent
active
048156493
DESCRIPTION:
BRIEF SUMMARY
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.
In 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, hetertofore has been carried out so as to be approved by the checking authorities or so as to be economically acceptable.
The present invention proposes a method of underwater explosive welding, at which the deficiencies of conventional 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 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 from joint surfaces at the explosive welding and, therefore, must be ground to a surface quality of Ra=2.5 .mu.m. 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 circumference. 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 hab
REFERENCES:
patent: 2367206 (1945-01-01), Davis
patent: 3503110 (1970-03-01), Berry
patent: 3578233 (1971-05-01), Meister
patent: 3672035 (1972-06-01), Lieberman
patent: 4231506 (1980-11-01), Istvanffy
Pipe to Pipe Welding by Explosives; M. D. Chadwick; Explosive Welding, 1976, pp. 31-33.
Modern Metals; Explosive Joining of Al. Pipe, Oct. 1962, p. 84.
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