Advanced Welding Technique

1. UNDER-WATER
WELDING
Soumyabrata
Basak

2. INTRODUCTION
 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.

3. CLASSIFICATION
• Under water welding can be classified as :
i. Wet welding
ii. Dry welding

4. WET 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

5. 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.

6. PRINCIPLE OF OPERATION
 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

7.  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

8. 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.

9. 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.

10. DRY 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.

11. CLASSIFICATION OF DRY WELDING
There are two basic types of dry welding :
i. Hyperbaric welding
ii. Cavity welding

12. 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”

13. Limitation:-
 As depth increase pressure also increases, it affects both
for driver and welding process

14. 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

15. Advantages:-
Welder/diver safety
Good quality weld
Surface monitoring
Non destructive testing

16. Disadvantages:-
The habitat welding requires large quantities of complex
equipment and much support equipment on the surface
Cost is extremely high

17. RISKS V/S 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

18. 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.

19. 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

21. CONCLUSION
Alternatives which include clamped and grouted
repairs (which may introduce unacceptably high
loading on offshore structures) and the use of bolted
flanges for the tie-ins are not necessarily and are not
always satisfactory

22. REFERENCES
 www.twi.com
 www.aws.com
 Production Technology- O.P.Khanna
 www.howstuffworks.com

23. THANK YOU