Under water welding.smnr

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  • 1. UNDERWATER WELDING Presented by Suresh Beera 12ETMM11 M.Tech/Ph.DMaterials Engineering1Wednesday, April 17, 2013SEST, UoH

2. OutlineImportance Of Underwater WeldingPrinciple Of OperationClassificationWet/Dry Underwater WeldingAdvantages& DisadvantagesRisk Involved & SafetyApplicationsFuture ScopeReferences2 Wednesday, April 17, 2013 3. 3 Wednesday, April 17, 2013 4. what is an Under water welding??? Many of us wont have heard of under water welding but its 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)4 Wednesday, April 17, 2013 5. Principle of Operation The 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.Waterproof ElectrodeHolderPower Supply_-+electrode work Knife switchFor wet welding AC is not used on account of electrical safety5and difficulty in maintaining an arc underwater April 17, 2013Wednesday, 6. 6 Wednesday, April 17, 2013 7. Underwater welding is classified into twocategories 1.Welding in-the-wet environment 2.Welding in-the-dry environment Dry weldingWet welding7 Wednesday, April 17, 2013 8. Welding in the wet environment As the name implies, underwater wet welding is donein an environment where the base metal and the arcare surrounded entirely by water. In wet welding MMA(manual metal arc welding) is used. A special electrode is used and welding is carried out manually justas one does in open air welding. The increased freedom of movement makes wet welding the most effective, efficient andeconomical method. Welding power supply is located on the surface with connection tothe diver/welder via cables8 Wednesday, April 17, 2013 9. Advantagescheapest and fastest methodtensile strength is higheasy of access the weld spotno habitat, no construction,no waste of time DisadvantagesRapid quenching decreases impact strength,ductilityHydrogen embrittlement,cracksPoor visibility in water9Wednesday, April 17, 2013 10. Hyperbaric(dry) welding Hyperbaric welding is a welding in which a chamber issealed around the structure to be welded and is filled withbreathable gas(commonly helium containing 0.5 bar ofoxygen) at the prevailing pressure. at which the weldingis to take place. This method produces high-quality weldjoints The gas tungsten arc welding process is employed forthis process. The area under the floor of the Habitat isopen to water. Thus the welding is done in the dry but atthe hydrostatic pressure of the sea water surrounding theHabitat10Wednesday, April 17, 2013 11. Dry welding11 Wednesday, April 17, 2013 12. 12 Wednesday, April 17, 2013 13. Advantages of Dry welding Welder/diver safety Good quality welds Surface monitoring Non destructive testing Disadvantages Higher cost of process,training,etc.,. Large quantity of costly and complex equipments. More deep,more energy is required Cant be weld,if weld spot is at unreachable places13Wednesday, April 17, 2013 14. Risk Involved & safety Electric 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 fromnitrogen introduced into the blood steam duringexposure to air at increased pressure. Precautions include the provision of an emergency air orgas supply, stand-by divers, and decompression chambersto avoid nitrogen Inspection of welds. 14 Wednesday, April 17, 2013 15. Application of Underwater WeldingOffshore construction for tapping sea resources, Temporary repair work caused byships collisions or unexpectedaccidents. Salvaging vessels sunk in the sea Repair and maintenance of ships Construction of large ships beyond the capacity of existing docks.15Wednesday, April 17, 2013 16. Scope for further developmentsWet MMA is still being used for underwaterrepairs, but the quality of wet welds is poor andare 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.Friction welding (FRW)Explosive and friction welding are also to be tested in deep waters. 16 Wednesday, April 17, 2013 17. REFERENCE Underwater Welding Present Status And FutureScope.Jyotsna Dutta Majumdar.Department OfMetallurgical And Materials Engineering, IndianInstitute Of Technology, Kharagpur, West Bengal,IndiaUnderwater Welding Amit Mukund Joshi (MechanicalEngineer) ,Junior Research Fellow MechanicalEngineering Department ,IndianInstituteOfTechnology ,I.I.T Bombay Annon, Recent Advances In Dry Underwater PipelineWelding, Welding Engineer, 1974. Lythall, Gibson, Dry Hyperbaric Underwater Welding,Welding Institute.17Wednesday, April 17, 2013 18. THANK YOU18 Wednesday, April 17, 2013