underwaterwelding
TRANSCRIPT
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UNDERWATER WELDINGTECHNOLOGY ,ART , COURAGE
SHOBHIT ISHAN
474/09
SEMINAR ON
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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’
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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.
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8Large habitat for underwater welding
Source: north stream
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9Large habitat underwater welding
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Advantages of dry welding
•Welder /diver safety•Good weld quality•Surface monitoring
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Disadvantages • 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
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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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•Power supply : DC 300 OR 400 AMP•Polarity : straight polarity
Requirements
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Effect of wet environment
• 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
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Effect of wet environment
Chemical composition
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Effect of wet environment
Porosity-troubleshooted by including Calcium carbonate
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Effect of wet environment•Microstructure•Mechanical properties
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Effect of wet environment
• Effect of alloying elements on weld metal microstructure and properties• Managanese• Boron and titanium• Rare earth metals
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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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Requirements for underwater welding
• 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.
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• Underwater Oxygen-Arc Welding Torches.- Collet or grip Oxygen valve Flash arrester
• Waterproofing Surface Electrodes. Epoxy 152Lee lac 30-l2093Polyurethane
Requirements for underwater welding
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Figure showing schematic diagram for underwater welding or cutting
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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