under water welding ppt
TRANSCRIPT
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Seminar On
Underwater welding
Submitted to: submitted by:Department of Mechanical MOHAN BIHARI
engineering 12EEJME029
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• First under water welding by British Admiralty – Dockyard
• In 1946, special waterproof electrodes were developed in Holland by ‘Van der Willingen’
• 1970s: Whitey Grubbs and Dale Anderson of Chicago Bridge & Iron (CB&I) qualified an underwater wet welding procedure to American Welding Society (AWS) standards.
History
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INTRODUCTION TO UNDERWATER WELDING
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We cant lift ship and then repair it. Hence comes the use of underwater welding
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Types of underwater welding
•Wet welding •Dry welding
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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.
Dry Welding
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Dry welding can be of two types•Large habitat•Mini habitat
Mini habitat for underwater welding. Large habitat for underwater
welding
9Large habitat underwater welding
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Advantages of dry welding
•Welder /diver safety•Good weld quality•Surface monitoring
• 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
Disadvantages
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Wet welding• 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
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FIGURES SHOWING WET WELDING
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• Cheapest• Fastest• Tensile strength is high• Ease of access the weld spot• No waste of time in constructing habitat
Advantages of wet welding
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• Rapid quenching decreases impact strength, Ductility.
• Hydrogen embrittlement.• Poor visibility in water.• Higher energy density of hydrogen, higher
efficiency.
Disadvantages
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Figure showing schematic diagram for underwater welding or cutting
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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.Repair and maintenance of underwater pipelines.
Application of underwater welding
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Dangers and difficulties
• 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.
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• 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
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Safety measures
• 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.
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• Precautions include achieving adequate electrical insulation of the welding equipment
• Areas and voids must be vented or made inert
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Future scope and developments
• 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.
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Thank you