It is for diploma students

1. UNDERWATER WELDING
Presented by
Akhil Mohan
Roll no : 14
S5.MECHANICAL
SEMINAR ON
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2. ➤ INTRODUCTION
• The first ever underwater welding was
carried out by British Admiralty - Dockyard
for sealing leaking ship rivets below the
water line. Underwater welding is an
important tool for underwater fabrication
works. In 1946, special waterproof
electrodes were developed in Holland by
Van der Willingen for underwater welding.
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3. Types of underwater welding
•Underwater welding can be classified as
•1) Wet Welding
•2) Dry Welding
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Dry Welding
Wet Welding

4. 4
Hyperbaric Welding (dry welding)
Hyperbaric welding is carried out in chamber sealed around
the structure to be welded. The chamber is filled with a gas
(commonly helium containing 0.5 bar of oxygen) at the
prevailing pressure. The habitat is sealed onto the pipeline
and filled with a breathable mixture of helium and oxygen,
at or slightly above the ambient pressure at which the
welding is to take place. This method produces high-quality
weld joints that meet X- ray and code requirements. The
gas tungsten arc welding process is employed for this
process. The area under the floor of the Habitat is open to
water. Thus the welding is done in the dry but at the
hydrostatic pressure of the sea water surrounding the
Habitat.

5. Advantages of dry welding
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1) Welder/Diver Safety
2) Good Quality Welds
3) Surface Monitoring
4) Non-Destructive Testing (NDT)

6. 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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7. WET WELDING
Wet Welding indicates that welding is performed underwater .
It is directly exposed to the wet environment. A special
electrode is used and welding is carried out manually just as
one does in open air welding. The increased freedom of
movement makes wet welding the most effective, efficient and
economical method. Welding power supply is located on the
surface with connection to the diver/welder via cables and
hoses.
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8. FIGURES SHOWING WET
WELDING
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9. • 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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10. • Rapid quenching decreases impact
strength, Ductility.
• Hydrogen embrittlement.
• Poor visibility in water.
• Higher energy density of hydrogen,
higher efficiency.
Disadvantages
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11. 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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Figure showing schematic diagram for
underwater welding or cutting

13. 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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14. • 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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15. 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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16. • Precautions include achieving adequate
electrical insulation of the welding
equipment
• Areas and voids must be vented or made
inert
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17. 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