When divers cut through parts of British Petroleum’s Magnus platform in one of the deepest parts of the North Sea, they were further in time from the Earth’s surface than astronauts on the Moon. They were carrying out repairs at depths up to 660ft (200m), and to avoid getting the ‘bends’ they had to spend more than eight days in decompression, before they were able to come to the surface.
Underwater cutting is often necessary for building or repairing oil platforms or pipelines. For example, a damaged pipe-line has to be cleanly cut before a new section can be welded to it, otherwise the weld would not hold.
There are two basic methods for cutting metal underwater; one is foxy-arc cutting, the other uses explosives. Oxy-arc cutting is a similar process to arc welding except that a supply of oxygen and a stronger electrical current are used to provide enough heat to cut right through the metal rather than just melt it.
For cutting through large pieces of metal, such as the leg of an oil platform
which is being dismantled, the oxy-arc method is used to make grooves in the metal into which plastic explosives are placed. As long as the right amount of explosive is used and it is positioned correctly, there should be no damage to the leg apart from a clean cut.
Picture Credit : Google
