Underwater welding is used for repairing offshore structures like oil rigs and pipelines. There are two types: wet welding, where welding occurs directly in water; and dry welding, where a chamber is created to keep water out. Wet welding uses manual metal arc welding and is cheaper but results in poorer quality welds due to quenching from water. Dry welding produces higher quality welds using gas tungsten or metal arc welding inside a pressurized chamber, but is more expensive. Precautions must be taken to prevent electric shocks and gas explosions when welding underwater. Research continues on welding deeper underwater through robotic technologies.

1. UNDER-WATER
WELDING

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 (inside the water)
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 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. Fig –(1)

9.  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

10. Advantages
Cost is low.
Less costlier than dry welding.
Speed with which it is carried out
No enclosures so no time is lost for building.

11.  Good surface finishing

13. 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 dust.

14. 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.

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

16. 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

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

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

19. Limitation:-
 As depth increase pressure also increases, it affects both
for driver and welding process
 It is unsafe process as compare to other welding process.

20. 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

21. 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.

23. 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

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

25. THANK YOU