meters (45 feet} helow the surface, in the stainless steel liner of a water- 

 filled storage pool. Habitats have been used to make underwater modifica- 

 tions to a drilling platform in the Gulf of Mexico. Hahitats can be con- 

 structed to surround the areas to be welded and filled with air so that 

 preheating of the weld areas is possible. Welds produced under these 

 conditions will basically have the same strength and ductility as welds 

 produced under the same condition topside. Habitats used in welding are 

 usually open at the bottom. Because of buoyancy, the habitat must be 

 securely attached and weighted. A constant flow of air through the habitat 

 is necessary to remove the fumes produced by welding, but electrolysis and 

 hydrogen formation is avoided because water is kept away from the arc. 



d. Underwater Cutting . Underwater cutting is used in salvage work and 

 wherever cutting below the waterline is required on steel structures such as 

 docks, piers, drilling platforms, and ships. The two most widely used 

 methods are flame cutting and oxygen arc cutting. 



The technique used for underwater flame cutting is not too different 

 from flame cutting steel in air. In each method, a fuel gas in a torch is 

 mixed with oxygen and burned to produce a flame that preheats the steel, and 

 a cutting jet is provided to supply oxygen to cut the steel. The underwater 

 cutting torch, however, contains one important difference in construction. 

 The underwater torch supplies its own ambient gas atmosphere, an air bubble 

 around the flame, by means of compressed air that is ejected through a 

 special nozzle surrounding the tip. An adjustable shield on the top of the 

 torch is also usually supplied to help control the formation of the air 

 bubble and to allow the torch to be held at the optimum distance from the 

 work, even under conditions of poor visibility and constraint due to the 

 cumbersome diving suits that must be worn. Slots are cut in the shield to 

 allow gases to escape. The underwater torch is furnished with three hoses, 

 for compressed air, oxygen, and fuel gas. 



Underwater flame cutting is most effective in severing a steelplate in 

 the thickness range of 12.7 to 152 millimeters (1/2 to 6 inches). Below 12.7 

 millimeters, the quenching effect of the water retards the cutting action 

 greatly. 



It is important that the air hose never be used for oxygen. Compressed 

 air may contain some oil which can coat the hose causing an explosion when 

 oxygen is introduced. Fuel gases are usually hydrogen or natural gas 

 because these gases can be used at any depth without liquifying. Acetylene 

 is almost never used in underwater cutting because at pressures more than 

 207 kilopascals (30 pounds per square inch) acetylene becomes unstable and 

 may decompose violently even if no oxygen is present. 



A standard welding power source, capable of supplying 300 amperes of 

 direct current straight polarity, is satisfactory for oxygen arc cutting 

 under water. Electrode holders are fully insulated and of a special design 

 so that both oxygen and current can be supplied to the electrode. To reduce 

 resistance losses, cables should be size 2/Q, except the last 3 meters (10 

 feet) at the torch which may he 1/0 for added flexibility. If the power 

 source is more than 120 meters (400 feet) from the work, parallel cables of 

 1/0 or 2/0 are required. All underwater cable connections should be wrapped 

 with rubber tape. A safety switch must be provided so that the torch is 

 energized only while cutting. 



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