Development of Welding Procedures for Critical Applications in Nuclear and Fossil Power Plants
I am involved in the several projects for development of materials, welding procedures and welding consumables for nuclear and Advanced Ultra Super Critical (AUSC) coal-fired power plants. As it is difficult to cover the entire work, I am presenting here some of the important and unique welding activities in this prestigious Prof. Placid Rodriguez Memorial lecture.
As a national mission program, research organizations and industries are working together for the development of new materials, fabrication technology, designing and construction of Indian Advanced Ultra Super Critical (AUSC) thermal power plant of 800 MWe capacity with steam parameters 710oC/720oC/310 bar. Indigenously developed Alloy 617M (a chemistry control variant of Alloy 617) and 304HCu SS are materials of choice for AUSC boiler tubes. Welding procedure has been developed and qualified for similar and dissimilar metal welding of Alloy 617M and 304HCu SS boiler tubes. Repair welding procedure for service exposed Alloy 617M has also been established. The dissimilar metal welding between 10Cr ferritic martensitic steel and nickel-base Alloy 617M rotor forgings for AUSC high pressure (HP) and intermediate pressure (IP) steam turbines is unique and first of its kind. For this, welding procedure, weld groove design and post weld heat treatment has been optimized using hot-wire narrow-gap TIG welding process, and mock-up weld joints are qualified as per ASME Section IX requirements. Root pass argon gas purging methodology in the localized cavity of solid welded rotor has also been established and qualified. Both NG-TIG welding procedure and root pass argon gas purging methodology has been successfully implemented in the fabrication of full-size welded rotor for AUSC project.
Similar and dissimilar welding of commercially pure titanium and 304L SS are required for the reprocessing of Fast Breeder Reactor nuclear spent fuel. The dissimilar metal joint between titanium and 304L stainless steel (SS) was carried out by explosive cladding process. The explosive cladded plates were qualified by ultrasonic examination, shear test, bend test and three phase (liquid, vapour, and condensate phase) corrosion test in 11.5M boiling nitric acid. The activated flux has been formulated in-house for autogenous TIG welding of titanium. The activated flux TIG weld joint fabricated using 6 mm thick titanium plate passed as per ASME section IX requirements and 11.5M boiling nitric acid test. This paper highlights some of the critical welding procedures developed for AUSC and nuclear power plants.
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