08-16-2017, 09:51 PM
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SUBMITTED BY:
Bhanu Pratap Singh
GUIDED BY:-
Mr. Brajesh Varshne
K A N P U R II N S T II T U T E O F T E C H N O L O G Y
INTRODUCTION
The fact that electric arc could operate was known for over a 100 years. The first ever underwater welding was carried out by British Admiralty Dockyard for sealing leaking ship rivets below the water line. 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, and platforms are being installed significantly. Some of these structures will experience failures of its elements during normal usage and during unpredicted occurrences like storms, collisions. Any repair method will require the use of underwater welding. Underwater welding provides a means to assemble or repair underwater. This is a highly useful technology available that allows repairs of ships damaged during hurricanes or wars. There are a couple of alternatives available, which include clamped and grouted repairs and bolted flanges. However, these alternatives do not always provide satisfactory results and also introduces high loading at offshore structures. Underwater welding is a highly specialized trade. Most are employed in the oil or shipping industry and the military.
CLASSIFICATION OF UNDERWATER WELDING
Underwater welding can be classified as 1) Wet Welding 2) Dry Welding In wet welding the welding is performed underwater, directly exposed to the wet environment. In dry welding, a dry chamber is created near the area to be welded and the welder does the job by staying inside the chamber.
WETWELDING
Wet Welding indicates that welding is performed underwater, directly exposed to the wet environment. A 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 and hoses. In wet welding MMA (manual metal arc welding) is used. It is carried out directly at ambient water pressure with the welder/diver in the water using water-proof stick electrode and without any physical barrier between water and welding arc [Oates, 1996]. Special precaution should be taken to produce underwater arc to protect it from surrounding water. Wet welding does not need any complicated experiment set up, it s economical and can be immediately applied in case of emergency and accident as it does not need water to be evacuated. However, difficulties in welding operation due to lack of visibility in water, presence of sea current, ground swells in shallow water and inferior weld qualities (increased porosities, reduced ductility, greater hardness in the heat affected zone, hydrogen pick up from the environment) are the notable disadvantages of wet welding technique.
Wet underwater welding commonly uses a variation of shielded metal arc welding, employing a waterproof electrode.[2] Other processes that are used include flux-cored arc welding and friction welding.[2] In each of these cases, the welding power supply is connected to the welding equipment through cables and hoses. The process is generally limited to low carbon equivalent steels, especially at greater depths, because of hydrogen-caused cracking.