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Under water welding.smnr


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Under water welding.smnr

  1. 1. UNDERWATER WELDING Presented by Suresh Beera 12ETMM11 M.Tech/Ph.D Materials Engineering•1 •Wednesday, April 17, 2013 SEST, UoH
  2. 2. Outline• Importance Of Underwater Welding• Principle Of Operation• Classification• Wet/Dry Underwater Welding• Advantages& Disadvantages• Risk Involved & Safety• Applications• Future Scope• References•2 •Wednesday, April 17, 2013
  3. 3. •3 •Wednesday, April 17, 2013
  4. 4. what is an Under water welding??? Many of us wont have heard of under water welding but its actually a very important thing in many industries. Underwater welding includes a lot of different processes that join steel on offshore oil platforms, pipelines & ships etc. under water. At present, underwater welding becomes more sophisticated and can be done deeper. GTAW has been used to weld pipes at depths of 200 ft (61 m)•4 •Wednesday, April 17, 2013
  5. 5. 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. Waterproof Electrode Holder Power Supply _ - + electrode work Knife switch •For wet welding AC is not used on account of electrical safety•5 and difficulty in maintaining an arc underwater April 17, 2013 •Wednesday,
  6. 6. •6 •Wednesday, April 17, 2013
  7. 7. Underwater welding is classified into two categories 1.Welding in-the-wet environment 2.Welding in-the-dry environment Dry welding Wet welding•7 •Wednesday, April 17, 2013
  8. 8. 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•8 •Wednesday, April 17, 2013
  9. 9. Advantages•cheapest and fastest method•tensile strength is high•easy of access the weld spot•no habitat, no construction,•no waste of time Disadvantages•Rapid quenching decreases impact strength,ductility•Hydrogen embrittlement,cracks•Poor visibility in water•9 • •Wednesday, April 17, 2013
  10. 10. 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•10 •Wednesday, April 17, 2013
  11. 11. Dry welding•11 •Wednesday, April 17, 2013
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  13. 13. Advantages of Dry welding •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•13 •Wednesday, April 17, 2013
  14. 14. Risk Involved & safety Electric shock Explosion. Precautions include achieving adequate electrical insulation of the welding equipment, shutting off the electricity supply immediately the arc is extinguished, and limiting the open-circuit voltage of MMA (SMA) welding sets Hydrogen and Oxygen are produced during welding. Precautions must be taken to avoid the build-up of pockets of gas, which are potentially explosive risk is to the life or health of the welder/diver from nitrogen introduced into the blood steam during exposure to air at increased pressure. Precautions include the provision of an emergency air or gas supply, stand-by divers, and decompression chambers to avoid nitrogen Inspection of welds. •14 •Wednesday, April 17, 2013
  15. 15. •Application of Underwater Welding •Offshore construction for tapping sea resources, • Temporary repair work caused by ship’s collisions or unexpected accidents. • Salvaging vessels sunk in the sea •Repair and maintenance of ships • Construction of large ships beyond the capacity of existing docks.•15 •Wednesday, April 17, 2013
  16. 16. •Scope for further developments •Wet MMA is still being used for underwaterrepairs, but the quality of wet welds is poor andare prone to hydrogen cracking. Dry Hyperbaric welds are better in quality than wet welds.Present trend is towards automation. THOR – 1 (TIG Hyperbaric Orbital Robot) is developed where diver performs pipefitting,.•Developments of driverless Hyperbaric welding system is an even greater challenge in developments like pipe preparation and aligning, automatic electrode. •This is in testing stage in deep waters. Friction welding (FRW) Explosive and friction welding are also to be tested in deep waters. •16 •Wednesday, April 17, 2013
  17. 17. REFERENCE  Underwater Welding –Present Status And Future Scope.Jyotsna Dutta Majumdar.Department Of Metallurgical And Materials Engineering, Indian Institute Of Technology, Kharagpur, West Bengal, India  Underwater Welding Amit Mukund Joshi (Mechanical Engineer) ,Junior Research Fellow Mechanical Engineering Department ,Indian Institute Of Technology ,I.I.T – Bombay  Annon, Recent Advances In Dry Underwater Pipeline Welding, Welding Engineer, 1974.  Lythall, Gibson, Dry Hyperbaric Underwater Welding, Welding Institute.•17 •Wednesday, April 17, 2013
  18. 18. THANK YOU•18 •Wednesday, April 17, 2013