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Diver using Oxy-hydrogen underwater cutting equipment.

Underwater cutting of Metals can be performed by Oxy-acetylene, Oxy-hydrogen or Oxy-electric . During the 1940's Oxy-hydrogen cutting was used widely for removing sunken debris such as wires, sunken ships, collapsed bridges etc. The operating temperature is around 2600 degrees C. Steel many inches thick can be cut successfully underwater.The basic principal is that a high pressure stream of pure oxygen is directed at a pre heated area so the metal which is melting is rapidly oxidised and removed to form a 'kerf'.or cut. Oxy-hydrogen is not as hot as Oxy-acetylene but can be used at greater depths. Compressed air is used to provide a protective shroud around the flame which in turn means the flame does not go out when immersed in water. Later Oxy-hydrogen cutting equipment such as the BOC Vixen and the Milne Seafire used only 2 hoses making fouling less likely. Oxy-electric was first used in the early 20th century. Electrodes are used which are made of steel or carbon. The surface to be cut is heated to the point of melting which is done by the electric arc. The electrode is tubular and oxygen passes through the bore of the rod or electrode. As soon as the electric arc is formed or 'struck' intense heat begins to melt the metal . A trigger is depressed and a stream of oxygen oxidises the molten metal . The electric current required is 550 amps with a DC voltage of 70-90 volts. Oxy-arc cutting is more suitable for cutting thinner metal as well as cast iron or non -ferrous metals. Coloured glasses are required for the oxy-electric process as the arc is intensely bright and damage to the eyes can easily occur giving rise to the condition known as Arc-eye.

Diver using Oxy-arc or Oxy-electric cutting equipment underwater.

The cutting of steel is a chemical rather than a mechanical action. It occurs when the locally pre heated steel becomes incandescent and impinged with a blast of oxygen at great pressure. The heat which melts the metal is created when an arc is created between the metal to be cut and the electrode or cutting rod. The heat is instantaneous and far hotter than the other methods. Cutting cast iron and non-ferrous metals is a much slower process.

Diver holding autogene cutting equipment.

Oxy-acetylene and Oxy-hydrogen both work on a similar principal. The combustion of either acetylene or hydrogen in oxygen causes a rapid expansion reaction. This reaction is trapped in a hood in the torch and with compressed air supplied from the surface a protective shroud is created in which the flame can burn when immersed in water. The rate of consumption of the gases is quite rapid so it can be an advantage to couple several bottles of gas to gether. If the flame should go out it was the practice to haul the torch to the surface to relight it . To overcome this a spark lighting device has been invented. A 12 volt lead is connected to a striker plate and another to the cutting torch head. The plate being made from cast iron . A signal is given to the tender and the current switched on .With all the gas valves open the nozzle of the cutter is rubbed against the striking plate and re ignition is achieved . The main operation difference between oxy-acetylene and oxy-hydrogen is the operating depth as oxy-acetylene cannot be used at depths greater than 30 feet although the flame is some 550 degrees hotter . The diver must first attain a degree of skill in the use of the equipment on the surface before attempting to use the equipment under water.

Producer: Picard
Country: France
Year: Circa 1920
Type: H7 La Soudure Autogene
Method of operation: Diver
One or two hand: Two Hand
Power source: Oxygen , Hydrogen , Compressed air
Depth rating: Diver's depth
Operating temperature: 2500 degrees C
Capacity: Several inches of steel

Artist's impression od a Diver using Underwater Cutting Equipment.

• Last edited 18th September 2006