Power plants need to carry out more expeditious and efficient operations by shortening the period of mechanical inspection. Tightening and loosening large-diameter bolts for steam and gas turbine casings is not only time-consuming but also typically dirty, dangerous, and difficult work for which improvement has been called for.
In the case of typical resistance wire bolt heater, the heating efficiency is low due to indirect heating by radiation and heat conduction, meaning it takes a long time for the temperature to rise. And because long hours of heating raise the temperature on the flange side as well, excessive elongation of bolts offer results. It also takes a long time for temperature on the flange side to decrease. In order to solve these problems, we developed our “Induction bolt heater” that can highly efficiently heat bolts using high frequency induction heating system and directly applying induction current to the bolt.
The technology used in this equipment was co-developed with Mitsubishi Hitachi Power Systems, Ltd. and commercialized to realize the safe, secure, and easy work of tightening and loosing hollow bolts in turbine casings and elsewhere. The technology helps shorten the construction period at each power plant, where it is used.
The induction bolt heater controls the input power to prevent bolts from weakening from rapid heating which is a specific character of induction heating, and controls the heating time to maintain the temperature range in which the yielding of bolt materials never occurs. Although input power and heating time are set according to the specifications of bolts, with our induction bolt heater, heating conditions are based on theoretical analysis backed by testing which ensures sufficient credibility.
Furthermore, our machine can be widely used for applications that include the assembly and disassembly of steam turbines (for power generation, ships, and as driving units, etc.),gas turbines, hydraulic turbines, diesel engines, pressure vessels, high pressure flanges, main stop valves, and other applications.