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Underwater welding

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Underwater welding

  1. 1. SEMINAR ON UNDERWATER WELDING TECHNOLOGY ,ART , COURAGE1 SHOBHIT ISHAN 474/09
  2. 2. • First under water welding by British Admiralty – Dockyard• In 1946, special waterproof electrodes were developed in Holland by ‘Van der Willingen’ 2
  3. 3. INTRODUCTION TOUNDERWATER WELDING 3
  4. 4. We cant lift ship and then repair it. Hence comes the use of underwaterwelding 4
  5. 5. •Wet welding 5 •Dry welding
  6. 6. Hyperbaric welding is the process in whicha chamber is sealed around the structure tobe welded and is filled with a gas ( He andOxygen) at the prevailing pressure. 6
  7. 7. Dry welding can be of two types•Large habitat•Mini habitat 7 Mini habitat for underwater welding.
  8. 8. Source: north streamLarge habitat for 8underwater welding
  9. 9. 9Large habitat underwater welding
  10. 10. •Welder /diver safety•Good weld quality•Surface monitoring 10
  11. 11. • Higher cost of process, training, etc• Large quantity of costly and complex equipments• More deep, more energy requirement.• Cant weld if weld spot is at unreachable place 11
  12. 12. • Simply means that job is performed directly in the water• It involves using special rod and is similar to the process in ordinary air welding 12
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  15. 15. • WATER-------------HYDROGEN + OXYGEN• Dissolve in weld pool• Solubility decrases and then comes out -  porosity• Oxygen as solid , liquid inclusions or gases• Hydrogen combines with oxygen forming vapour 15
  16. 16. Chemical composition 16
  17. 17. Porosity-troubleshooted by including Calciumcarbonate 17
  18. 18. •Microstructure•Mechanical properties 18
  19. 19. • Effect of alloying elements on weld metal microstructure and properties • Managanese • Boron and titanium • Rare earth metals 19
  20. 20. • Cheapest• Fastest• Tensile strength is high• Ease of access the weld spot• No waste of time in constructing habitat 20
  21. 21. • Rapid quenching decreases impact strength, Ductility.• Hydrogen embrittlement.• Poor visibility in water.• Higher energy density of hydrogen, higher efficiency. 21
  22. 22. • Power supply requrements-400 amp or larger. DC generators, motor generators and rectifiers are acceptable power supplies• Power converters.• Welding Generator, Pre-Setup• Polarity.• Diesel Driven Welding Generator Amperage and Voltage settings.• Gas Manifolds. 22
  23. 23. • Underwater Oxygen-Arc Welding Torches.- Collet or grip Oxygen valve Flash arrester• Waterproofing Surface Electrodes. Epoxy 152 Lee lac 30-l2093 Polyurethane 23
  24. 24. Figure showing schematic diagram forunderwater welding or cutting 24
  25. 25. • Hydrogen and oxygen are dissociated from the water and will travel separately as bubbles• Oxygen cutting is about 60 percent efficient• Above river beds, especially in mud, because trapped methane gas in the proper concentrations can explode. 25
  26. 26. • There is a risk to the welder/diver of electric shock.• There is a risk that defects may remain undetected• The other main area of 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 26
  27. 27. • Start cutting at the highest point and work downward• By withdrawing the electrode every few seconds to allow water to enter the cut• Gases may be vented to the surface with a vent tube (flexible hose) secured in place from the high point where gases would collect to a position above the waterline. 27
  28. 28. • Precautions include achieving adequate electrical insulation of the welding equipment• Areas and voids must be vented or made inert 28
  29. 29. • Development of alternative welding methods like friction welding, explosive welding, and stud welding.• Present trend is towards automation. THOR – 1 (TIG Hyperbaric Orbital Robot) is developed where diver performs pipefitting, installs the track and orbital head on the pipe and the rest process is automated. 29
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