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UNDERWATER WELDINGPresented byRAVINDHER GAJA CBITThursday, March 13, 20141Outline Importance Of Underwater WeldingPrinciple Of OperationClassificationWet/Dry Underwater WeldingAdvantages& DisadvantagesRisk Involved & Safety ApplicationsFuture ScopeReferences

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13-Mar-143Thursday, March 13, 20144 what is an Under water welding???Many of us won't have heard of under water welding but it's actually a very important thing in many industries. Underwater welding includes a lot of different processes that join steel on offshore oil platforms, pipelines & ships etc. under water. At present, underwater welding becomes more sophisticated and can be done deeper. GTAW has been used to weld pipes at depths of 200 ft (61 m)

13-Mar-144At present, underwater welding becomes more sophisticated and can be done deeper. GTAW has been used to weld pipes at depths of 200 ft (61 m) and has produced an X-ray quality welds meeting the requirements of API 1104 Standard. Offshore oil explorations have increased the interest in underwater welding.Thursday, March 13, 20145Principle of Operation

_Power Supply - +workKnife switchelectrodeWaterproof ElectrodeHolderThe welding circuit must include a positive type of switch, usually a knife switch operated on the surface and commanded by the welder and is used for safety reasons. When DC is used with +ve polarity, electrolysis will take place and cause rapid deterioration of any metallic components in the electrode holder.

For wet welding AC is not used on account of electrical safety and difficulty in maintaining an arc underwater

13-Mar-145Wet Underwater Welding method uses a waterproof welding electrodes. The power of the arc generates a bubble of a mixture of gasses which lets metal melting and joining occur more or less normal.Thursday, March 13, 20146

Thursday, March 13, 20147Underwater welding is classified into two categories1.Welding in-the-wet environment 2.Welding in-the-dry environmentDry weldingWet welding

Thursday, March 13, 20148As the name implies, underwater wet welding is done in an environment where the base metal and the arc are surrounded entirely by water. In wet welding MMA (manual metal arc welding) is used.

Welding in the wet environmentA special electrode is used and welding is carried out manually just as one does in open air welding.The increased freedom of movement makes wet welding the most effective, efficient and economical method. Welding power supply is located on the surface with connection to the diver/welder via cables 13-Mar-148The power of the arc generates a bubble of a mixture of gasses which lets metal melting and joining occur more or less normal.

Thursday, March 13, 20149Advantagescheapest and fastest methodtensile strength is higheasy of access the weld spotno habitat, no construction, no waste of time

Disadvantages Rapid quenching decreases impact strength, ductilityHydrogen embrittlement,cracksPoor visibility in water

Hyperbaric(dry) weldingHyperbaric welding is a welding in which a chamber is sealed around the structure to be welded and is filled with breathable gas(commonly helium containing 0.5 bar of oxygen) at the prevailing pressure. at which the welding is to take place. This method produces high-quality weld jointsThe gas tungsten arc welding process is employed for this process. The area under the floor of the Habitat is open to water. Thus the welding is done in the dry but at the hydrostatic pressure of the sea water surrounding the Habitat

Thursday, March 13, 20141013-Mar-1410The bottom portion of the chamber is exposed to open water and is covered by a grating. This is done to equalize the chamber pressure to the outside water pressure at certain depth. The chamber provides the welder/diver with all necessary welding equipment for welding in a dry environment.Dry weldingThursday, March 13, 201411

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Thursday, March 13, 201413Advantages of Dry weldingWelder/diver safetyGood quality weldsSurface monitoringNon destructive testingDisadvantagesHigher cost of process,training,etc.,.Large quantity of costly and complex equipments.More deep,more energy is requiredCant be weld,if weld spot is at unreachable places

Risk Involved & safety Thursday, March 13, 201414Electric shock Explosion.Precautions include achieving adequate electrical insulation of the welding equipment, shutting off the electricity supply immediately the arc is extinguished, and limiting the open-circuit voltage of MMA (SMA) welding sets

Hydrogen and Oxygen are produced during welding.Precautions must be taken to avoid the build-up of pockets of gas, which are potentially explosive

risk is to the life or health of the welder/diver from nitrogen introduced into the blood steam during exposure to air at increased pressure. Precautions include the provision of an emergency air or gas supply, stand-by divers, and decompression chambers to avoid nitrogen

Inspection of welds.

Thursday, March 13, 201415Application of Underwater Welding

Offshore construction for tapping sea resources, Temporary repair work caused by ships collisions or unexpected accidents. Salvaging vessels sunk in the seaRepair and maintenance of ships Construction of large ships beyond the capacity of existing docks.

Thursday, March 13, 201416Scope for further developments Wet MMA is still being used for underwater repairs, but the quality of wet welds is poor and are prone to hydrogen cracking. Dry Hyperbaric welds are better in quality than wet welds. Present trend is towards automation. THOR 1 (TIG Hyperbaric Orbital Robot) is developed where diver performs pipefitting,. Developments of driverless Hyperbaric welding system is an even greater challenge in developments like pipe preparation and aligning, automatic electrode. This is in testing stage in deep waters. Explosive and friction welding are also to be tested in deep waters.

Friction welding (FRW)Thursday, March 13, 201417REFERENCE

Underwater Welding Present Status And Future Scope.Jyotsna Dutta Majumdar.Department Of Metallurgical And Materials Engineering, Indian Institute Of Technology, Kharagpur, West Bengal, India Underwater Welding Amit Mukund Joshi (Mechanical Engineer) ,Junior Research Fellow Mechanical Engineering Department ,Indian Institute Of Technology ,I.I.T Bombay Annon, Recent Advances In Dry Underwater Pipeline Welding, Welding Engineer, 1974. Lythall, Gibson, Dry Hyperbaric Underwater Welding, Welding Institute.

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