abhishek jain underwater welding
TRANSCRIPT
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1
Study of Various Methods and
Parameters Involved in Underwater Welding
Subject Code-ME1637
Under the guidance of:Dr. A K Das
Presented By:
Abhishek Jain
1201076
Department of Mechanical Engineering
National Institute of Technology Patna
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2Contents Introduction
Classification
Wet Welding
Dry Welding
Advantages
Disadvantages
Schematic Diagram of Apparatus Required
Risks
Applications
Effect of Wet environment on welds
Porosity Curve
References
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3INTRODUCTION TO UNDERWATER WELDING
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How can big ships or underwater Rigs be repaired ????We can’t lift ships and then repair them.
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5INTRODUCTION
Underwater welding is an important tool for
underwater fabrication works.
In 1946, special waterproof electrodes were
developed in Holland by ‘Vander Willingen'’.
In recent years the number of offshore structures
including oil drilling rigs, pipelines, platforms are
being installed significantly.
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6CLASSIFICATION
• Under water welding can be classified as :
i. Dry welding
ii. Wet welding
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7DRY WELDING
A chamber is created near the area to be welded and the welder does the job by staying inside the chamber.
It produces high quality weld joints .
The gas-tungsten arc welding process is used mostly for pipe works
Gas metal arc welding is the best process for this welding.
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8CLASSIFICATION OF
DRY WELDING
There are two basic types of dry welding :
i. Hyperbaric welding
ii. Cavity welding
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9Hyper baric welding:-
It is carried out in chamber sealed around the structure to be welded filled with a gas to push water back.
Gas generally used is a breathable mixture of helium and oxygen.
The area under the floor of the habitat is open to water, so hyper baric welding is termed as
“HABITAT-WELDING”
An image for Habitat Welding
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Hyper = High, Baric = Pressure
Hyper Baric welding means high Pressure Welding
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11Cavity welding:-
Cavity welding is another approach to weld in water free environment.
Conventional arrangements for feeding wire and shielding gas
Introducing cavity gas and the whole is surrounded by a trumpet shaped nozzle through which high velocity conical jet of water passes.
It avoids the need for a habitat chamber and it lends itself to automatic and remote control.
The process is very suitable for flat structures.
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Advantages:-
Welder/diver is safe.
Good quality
welds are formed.
Surface monitoring of welders condition can
be done.
Non destructive testing of weld is
easy.
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13Disadvantages:-
The habitat welding requires large quantities of complex equipment and much support equipment on the surface
Cost is extremely high hence cannot be afforded by normal or small firms.
Large habitat for underwater hyperbaric welding
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14WET WELDING
Key technology for repairing marine structure
Welding is performed under water directly exposed to the wet environment
Increased freedom movement makes more effective, efficient and economical
Supply is connected to the welder/driver via cables
or hoses
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Complete insulation of the
cables and hoses are
essential in case to prevent
the chance for electric
shock
MMA (Manual Metal Arc)
welding is commonly used
process in the repair of
offshore platforms.
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PRINCIPLE OF OPERATION
The work-piece is connected to the positive side of dc source (Anode) and electrode to the negative side (Cathode).
The two parts of the circuit are brought together and then slightly separated.
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17 An electric current
occurs in the gap and causes a sustained spark which melts the bare metal forming a weld pool.
The flux covering the electrode melts to provide a shielding gas.
Arc burns in the cavity formed inside the flux covering, which is designed to burn slower than the metal barrel to the electrode.
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18Advantages
The versatility and low cost.
Less costlier than dry welding.
Speed with which it is carried out.
No enclosures so no time is lost for building.
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19Disadvantages
Rapid quenching of the weld metal by the surrounding water.
Welders working under water are restricted in manipulating arc.
Hydrogen embrittlement causes cracks.
Poor visibility due to water contaminance.
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20RISKS V/S PRECAUTIONS
Risk of electric shock so precaution is taken for checking the electrical insulation of electrical welding equipments.
Hydrogen and oxygen are produced by the arc in wet welding which are potentially explosive so precaution must be taken to avoid the build up of pockets of gas
The life or health of the welder will be in risk from nitrogen introduction into the blood stream, hence precautions include the provision of an emergency air cylinder for the welder.
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APPLICATIONS
Offshore construction for tapping sea resources.
Temporary repair work caused by ship’s collisions, or unexpected accidents.
Salvaging vessels sunk in the sea.
Construction of large ships beyond the capacity of existing docks.
Maintenance of oil rigs.
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Figure showing schematic diagram for underwater welding or cutting
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EFFECT OF WET ENVIRONMENTWater dissociates into Oxygen and Hydrogen which dissolves in the molten pool causing: Gas Inclusion Defects Porosity Water Inclusion as after some times hydrogen combines with
oxygen forming water vapor.
V-groove wet weld deposited at 100 m depth (a) and its radiographic image (b)
(a)
(b)
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Graph Between the Porosity and Water Pressure during welding
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• Most Underwater Structures are formed using this method as the
method is economical, flexible, versatile, Speedy.
• Combined additions of titanium, boron, and manganese increased
the tensile strength of the steel wet welds due to microstructural
refinement and increased hardenability thus providing new
dimensions to underwater structures
CONCLUSION
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26REFERENCES
www.Wikipedia.org
Paper on Underwater Welding-Jyotsana Dutta
Majumdar (IIT KGP 2006)
Manual for underwater welding, US Navy
www.howstuffworks.com
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THANK YOU