A finite element approach to renew underwater shell plate of a dumb barge sans dry docking: an innovative and cost-effective model

摘要

Sagar Shakti, a million litre/day desalination dumb barge belonging to the National Institute of Ocean Technology (NIOT), was damaged on its underwater hull during deployment of a mooring buoy at 1000 m depth. The shell plate had several perceptible wide punctures leading to rapid seepage of sea water into void spaces. Shipyards on the east coast of India expressed inability to renew the shell plate and insisted on dry docking as the only possible way. Owing to financial and time constraints combined with severe monsoon conditions, the barge could not be towed. A suitable water-tight chamber was designed and fabricated to use it as a cofferdam with ceramic back strip welding. Finite element analysis on the water-tight chamber showed that the design was optimum. Welding was done inside the hull; molten metal fills the gap between two plates of butt joint, thereby eliminating external welding. Non-destructive tests including radiography showed the perfection of the weld joint. It was a successful work after which the barge was put into operation to demonstrate a desalination plant. This kind of underwater shell plate renewal without dry docking was done for the first time in India under class approval, thereby saving the huge cost of dry docking, and provided an innovative idea to the" industry.