4. what is an Under water welding???
Many of us won't have heard of under water welding but
it's actually a very important thing in many industries.
Underwater welding includes a lot of different processes
that join steel on offshore oil platforms, pipelines & ships
etc. under water. At present, underwater welding becomes
more sophisticated and can be done deeper. GTAW has
been used to weld pipes at depths of 200 ft (61 m)
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5. Principle of Operation
•The welding circuit must include a positive type of switch, usually
a knife switch operated on the surface and commanded by the
welder and is used for safety reasons.
•When DC is used with +ve polarity, electrolysis will take place
and cause rapid deterioration of any metallic components in the
electrode holder.
Waterproof Electrode
Holder
Power Supply
_
- +
electrode
work
Knife switch
•For wet welding AC is not used on account of electrical safety
•5 and difficulty in maintaining an arc underwater April 17, 2013
•Wednesday,
7. Underwater welding is classified into two
categories
1.Welding in-the-wet environment
2.Welding in-the-dry environment
Dry welding Wet welding
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8. Welding in the wet environment
As the name implies, underwater wet welding is done
in an environment where the base metal and the arc
are surrounded entirely by water. In wet welding MMA
(manual metal arc welding) is used.
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
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9. Advantages
•cheapest and fastest method
•tensile strength is high
•easy of access the weld spot
•no habitat, no construction,
•no waste of time
Disadvantages
•Rapid quenching decreases impact strength,
ductility
•Hydrogen embrittlement,cracks
•Poor visibility in water
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10. Hyperbaric(dry) welding
Hyperbaric welding is a welding in which a chamber is
sealed around the structure to be welded and is filled with
breathable gas(commonly helium containing 0.5 bar of
oxygen) at the prevailing pressure. at which the welding
is to take place. This method produces high-quality weld
joints
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
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13. Advantages of Dry welding
•Welder/diver safety
•Good quality welds
•Surface monitoring
•Non destructive testing
Disadvantages
•Higher cost of process,training,etc.,.
•Large quantity of costly and complex
equipments.
•More deep,more energy is required
•Can’t be weld,if weld spot is at
unreachable places
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14. Risk Involved & safety
Electric shock Explosion.
Precautions include achieving adequate electrical
insulation of the welding equipment, shutting off the
electricity supply immediately the arc is extinguished, and
limiting the open-circuit voltage of MMA (SMA) welding sets
Hydrogen and Oxygen are produced during welding.
Precautions must be taken to avoid the build-up of pockets
of gas, which are potentially explosive
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.
Precautions include the provision of an emergency air or
gas supply, stand-by divers, and decompression chambers
to avoid nitrogen
Inspection of welds.
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15. •Application of Underwater Welding
•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.
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16. •Scope for further developments
•Wet MMA is still being used for underwater
repairs, but the quality of wet welds is poor and
are prone to hydrogen cracking. Dry Hyperbaric
welds are better in quality than wet welds.
Present trend is towards automation. THOR – 1
(TIG Hyperbaric Orbital Robot) is developed
where diver performs pipefitting,.
•Developments of driverless Hyperbaric welding
system is an even greater challenge in
developments like pipe preparation and
aligning, automatic electrode.
•This is in testing stage in deep waters. Friction welding (FRW)
Explosive and friction welding are also to be
tested in deep waters.
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17. REFERENCE
Underwater Welding –Present Status And Future
Scope.Jyotsna Dutta Majumdar.Department Of
Metallurgical And Materials Engineering, Indian
Institute Of Technology, Kharagpur, West Bengal,
India
Underwater Welding Amit Mukund Joshi (Mechanical
Engineer) ,Junior Research Fellow Mechanical
Engineering Department ,Indian Institute Of
Technology ,I.I.T – Bombay
Annon, Recent Advances In Dry Underwater Pipeline
Welding, Welding Engineer, 1974.
Lythall, Gibson, Dry Hyperbaric Underwater Welding,
Welding Institute.
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