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7862 |
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Wednesday, September 13, 2023, Brüssel 12:00 PM Application of underwater welding |
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Analysis of Structural integrity on Underwater wet welding in Maritime |
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Ramesh Babu Govindaraj* / DNV, Norway Per Lindström / Linnaeus University, Sweden Uwe Aschemeier/ Subsea Global Solutions, USA |
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Maritime ship and offshore structure require high maintenance and periodic check by ship classification society. Survey or inspection underwater is a challenge and it shall be done by a qualified and approved diving company for visual inspection and if there is any defect it shall be rectified before the voyage. Presently we have many cases increasing the ship owner and operator look for the repair in- water to save the time and to avoid docking the ship in dry dock which cost higher. DNV as classification society get query for acceptance of wet welding at different location which is below the draft line of vessel main on rudder, buildup of wasted seams at side shell, bottom plate, overboard pipe penetration, bilge keel etc. Wet underwater welding technique possesses a high cooling rate as the weld metal and welding arc are in straight contact with water. The high cooling rate of wet underwater welding drives the creation of a martensitic structure that impacts the weld metal's strength and HAZ properties which is a major concern for DNV. Besides the cooling rate, a drawback of underwater weld is the unsteady arc of electrodes while welding because of the hydrostatic pressure of water, and hence its penetration is not as good as the air. Proper qualified welding technique, experience welder can make a great difference to the welded joint achieved strength. In the underwater wet welding process, the temperature of the wire tip rises sharply as soon as contacting with the workpiece, so that the surrounding water is rapidly vaporized to form an arc bubble. As the arc burns in the bubble, the gas in the arc bubble increases sharply and periodically rises. When the arc bubble floats, the arc length changes drastically, and the welding process is in a metastable state. Scientific Oral presentation brief description: DNV had evaluated each case by case for allowing the wet welding with stringent requirement in addition the AWS D3.6 standard. DNV had made a repair guidance DNV-CG-0467 for the owner and operator by the author of this paper. In this presentation we will discuss about underwater welding procedure qualification studies which was carried out at 6mt water depth on low carbon VL D36 grade steel for accepting fit for purpose. |