Underwaterwelding

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Underwaterwelding

  1. 1. UNDERWATER WELDING TECHNOLOGY ,ART , COURAGE SHOBHIT ISHAN 474/09 SEMINAR ON 1
  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 TO UNDERWATER WELDING 3
  4. 4. We cant lift ship and then repair it. Hence comes the use of underwater welding 4
  5. 5. •Wet welding •Dry welding 5
  6. 6. Hyperbaric welding is the process in which a chamber is sealed around the structure to be welded and is filled with a gas ( He and Oxygen) at the prevailing pressure. 6
  7. 7. Dry welding can be of two types •Large habitat •Mini habitat Mini habitat for underwater welding. 7
  8. 8. Large habitat for underwater welding Source: north stream 8
  9. 9. 9 Large 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
  13. 13. 13
  14. 14. ‹#›
  15. 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
  16. 16. 16 Chemical composition
  17. 17. 17 Porosity-troubleshooted by including Calcium carbonate
  18. 18. 18 •Microstructure •Mechanical properties
  19. 19. 19 • Effect of alloying elements on weld metal microstructure and properties • Managanese • Boron and titanium • Rare earth metals
  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. 24 Figure showing schematic diagram for underwater welding or cutting
  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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