Underwater Welding by Diver

Principle of Operation

• The welding circuit must include a positive type of switch, usually a knife switch operated on the surface and commanded by the welder and is used for safety reasons
• When DC is used with +ve polarity, electrolysis will take place and cause rapid deterioration of any metallic components in the electrode holder.
  
  
  
• For wet welding AC is not used on account of electrical safety and difficulty in maintaining an arc underwater

Categories

1. Welding in the wet environment
   As the name implies, underwater wet welding is done in an environment where the base metal and the arc are surrounded entirely by water. In wet welding MMA (manual metal arc welding) is used. A special electrode is used and welding is carried out manually just as one does in open air welding. The increased freedom of movement makes wet welding the most effective, efficient and economical method. Welding power supply is located on the surface with connection to the diver/welder via cables.
   
   
   
   
   Adventage :
• cheapest and fastest method
• tensile strength is high
• easy of access the weld spot
• no habitat, no construction
• no waste of time Disadvantage
• Rapid quenching decreases impact strength,ductility
• Hydrogen embrittlement,cracks
• Poor visibility in water
2. Hyperbaric(dry) welding
   Hyperbaric welding is a welding in which a chamber is sealed around the structure to be welded and is filled with breathable gas(commonly helium containing 0.5 bar of oxygen) at the prevailing pressure. at which the welding is to take place. This method produces high-quality weld joints. The gas tungsten arc welding process is employed for this process. The area under the floor of the Habitat is open to water. Thus the welding is done in the dry but at the hydrostatic pressure of the sea water surrounding the Habitat
   
   
   
   
   Advantage :
• Welder/diver safety
• Good quality welds
• Surface monitoring 
• Non destructive testing Disadvantages 
• Higher cost of process,training,etc.,. 
• Large quantity of costly and complex equipments.
• More deep,more energy is required 
• Can’t be weld,if weld spot is at unreachable places

Reference:

http://www.slideshare.net/chuchu42/under-water-weldingsmnr