presented by:- swapnil s. chille te-mechanical exam no:-
TRANSCRIPT
UNDER-WATER
WELDING
Presented by:-SWAPNIL S. CHILLETE-MechanicalExam no:-
Very High Pressure
Very Low Temperature
Wet Gas Dissolved in Water
In this condition normal welding is impossible
Under water welding method enables us to weld properly under this condition.
Under water welding is an important tool for under water fabrication work.
What is under water welding?
Under water welding is the process of welding at elevated pressures, normally underwater.
A number of different welding techniques can be used underwater.
HISTORY
The first ever under water welding was carried out by British Admiralty for sealing leaking ship rivets below the water line.
In 1946 special waterproof electrodes were developed in Holland by Van Der Willingen.
UNDER WATER WELDING
WET WELDING DRY/HYPERBARIC WELDING
TYPES OF UNDER WATER WELDING
WET WELDING
Wet Welding indicates that welding is performed underwater, 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.
Supply is connected to the welder/driver via cables or hoses
MMA (Manual Metal Arc) welding is commonly
used process in the repair of offshore platforms.
Complete insulation of the cables and hoses are
essential in case to prevent the chance for electric
shock
The work is connected to the positive side of dc source and electrode to the negative
The two parts of the circuit are brought together and then slightly separated
An electric current occurs in the gap and causes a sustained spark which melts the bare metal forming a weld pool
PRINCIPLE OF OPERATION
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
Advantages
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.
Disadvantages
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.
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.
DRY WELDING
CLASSIFICATION OF DRY WELDING
There are two basic types of dry welding :
i. Hyperbaric welding
ii. Cavity welding
Hyper baric welding:-
It is carried out in chamber sealed around the structure to be welded
The chamber is filled with a gas at the prevailing pressure, to push water back
The welder fitted with breathing mask and other protective devices on the pipe line
Mask filled with a breathable mixture of helium and oxygen in the habitat
The area under the floor of the habitat is open to water, so hyper baric welding is termed as “HABITATWELDING”
Limitation:-
As depth increase pressure also increases, it affects
both for driver and welding process
Cavity 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
Advantages:-
Welder/diver safety
Good quality weld
Surface monitoring
Non destructive testing
Disadvantages:-
The habitat welding requires large quantities of
complex equipment and much support equipment on
the surface
Cost is extremely high
RISKS & PRECAUTIONS
Risk of electric shock so achieving electrical insulation of electrical welding equipments
Hydrogen and oxygen are produced by the arc in wet welding are potentially explosion 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 introduce into the blood stream, precautions include the provision of an emergency air or gas applied
Scope of further developments Hyper baric welding is well established and generally
well researched. Research being carried out for welding at a range of
500 to 1000m deep. THOR-1 (Tig Hyperbaric Orbital Robot) is developed
where diver performs pipe fitting, installs the tracks and orbital head on the pipe and rest process is automated.
APPLICATIONS
Offshore construction for tapping sea resources Temporary repair work caused by ship’s collisions,
unexpected accidents Salvaging vessels sunk in the sea Repair and maintenance of ships Construction of large ships beyond the capacity of
existing docks
APPLICATIONS
Thank You