Underwater welding

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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.

8Large habitat for underwater welding

Source: north stream

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