An Investigation on the Causes of a Rotor Bending and its Thermal Straightening (TECHNICAL NOTE)

Distortion or bend in a turbine rotor (especially HIP rotors) may be caused by a number of factors, either singularly or in combination. In general, the causes of rotor bend can be classified invariably in two categories: Rapidly forming permanent rotor bends and/or Slower forming rotor bends, which could trip the turbines’ emergency stop. One of the major modifying solutions for rapid repairing of bent rotors is hot spotting. For this purpose, after the initial tests (visual inspection, chemical analysis, nondestructive hardness), the hot spotting was performed seven consecutive times. The results of experimental investigations and experiences with different temperatures and times showed that, the 690 ± 20˚C and 210 S. are as an optimum temperature and time respectively, for hot spotting which can provide a noticeable straightening in bent areas, in addition to having no affects on mechanical properties. Also, this results were simulated by F.E.M in view of heat distribution in different temperatures in three states (without insulation, with moisture and dry insulation), in order to find out the optimum restraint effects around hot spot area.