Structural Safety of Rotor Discs for Steam Turbines
Rotor discs are key parts of COPT (Cargo Oil Pump Turbine) in large vessels. A rotor disc is composed of a lot of turbine blades, their covers, and a rotor shaft. Currently, rotor discs are fabricated by manual riveting of blades and covers. Riveting is a traditional manufacturing process, which entangles separate parts into one assembly. However, it consumes a lot of time for manufacturing and may cause damages on the surfaces of the assembly if hammering missing the mark. Once blades are riveted, then it is very hard to replace some damaged ones. Since the processing time for riveting is long, the manufacturing cost for a rotor disc is high. Because of these problems in producing rotor discs, the fabrication by riveting should be replaced with an assembly type. This paper redesigns a rotor disc for an assembly type. The main concept is the roots of blades are inserted into a rotor shaft securely. The heads of blades should sustain themselves by pushing each other without breakaway. These entanglement must be strong enough to sustain themselves. On order to assure their binding, this research proves it with the simulation for structural analysis and durability tests using commercial software. Working pressure on the blade is one M Pascal with 3,600 rpm at 374 degree Celsius. From the simulation, the maximum displacement is 0.0545mm and max 146.59 M Pascal of stress. The fatigue life is shown 2.7x10^7 cycles and the fatigue safety index 1.36 minimum. The max fatigue failure index is 0.736. From the simulations this research concludes that the assembly type rotor disc is safe in its operation in mechanical. The riveting type rotor disc should be replaced with the assembly type redesigned in this research.
Index Terms - Steam turbines, stress analysis, structural safety, COPT