Underwater welding is an important technique for fabrication and repair of marine structures. It was developed in 1946 when special waterproof electrodes were created in Holland. There are two main types of underwater welding: welding performed directly in water and hyperbaric welding which is done inside a pressurized chamber. Manual metal arc welding is commonly used for repairs of offshore platforms due to its versatility and low cost. Research continues on techniques like hyperbaric welding to enable welding at depths of 500 to 1000 meters. Underwater welding is used for offshore construction, ship repair and maintenance, and construction of large ships.

2. S.SARAVANA KUMAR

6. INTRODUCTION
•Underwater welding is an important tool for
under fabrication work.
•In 1946,special water proof electrodes were
developed in HOLLAND by EVANDER WILLINGEN.

7. CLASSIFICATION
Under water welding can be classified as :

8. •This technology for repairing marine structure.
•welding is performed under water directly
exposed to the wet environment.
•MMA (manual metal arc) welding is commonly
used process in repair of offshore platform.

9. electrode
•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 gap and causes a
sustainable spark which melts the bare metal to
provide a shielding gas.
•Arc burns in the cavity formed inside the flux
covering , which designed to burn slower than the
metal barrel to the electrode.

10. •Less costlier than dry
welding.
•The versatility and low
cost.
Disadvantage
•Hydrogen embritt lement causes cracks.
•poor visibility due to water contaminance.

11. •A chamber is created near the area to be the
welded.
•The welder does the job by staying inside the
chamber.
•Gas metal arc welding is the best process
for this welding.

12. •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 is developed performs pipe fitting, installs
the track and orbital head on pipe and rest process
is automated.

13. •Offshore construction for taping sea
resources.
•Repair and maintenance of ship.
•Construction of large ship beyond
the capacity of existing docks.

14. Alternative which include clamped
and grouted repairs and the use of
bolted flanges for the tie-ins not
necessarily and are not always
satisfactory.