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Nondestructive Evaluation of Remanent Life of Turbine Rotor Steel by Measuring Reversible Magnetic Permeability  

Ryu, Kwon-Sang (Division of Electromagnetic Metrology, Korea Research Institute of Standards and Science)
Nahm, Seung-Hoon (Division of Electromagnetic Metrology, Korea Research Institute of Standards and Science)
Kim, Yong-Il (Division of Electromagnetic Metrology, Korea Research Institute of Standards and Science)
Publication Information
Journal of the Korean Society for Nondestructive Testing / v.23, no.4, 2003 , pp. 315-321 More about this Journal
Abstract
The integrity of the turbine rotors can be assessed by measuring the material properties at service temperature. In order to evaluate the remanent life of turbine rotor steel nondestructively, a measurement system of reversible magnetic permeability using an alternating perturbing magnetic field was constructed. We present a new non-destructive method to evaluate the remanent life of 1Cr-1Mo-0.25V steel using the value of reversible magnetic permeability. This method is based on the existence of reversible magnetic permeability in the differential magnetization around the coercive field strength. We measured the first harmonics voltage induced in a coil using a lock-in amplifier tuned to an exciting frequency. The Results of reversible magnetic Permeability and Wickers hardness on the aged samples show that the peak interval of reversible magnetic permeability (PIRMP) and Vickers hardness decreases as aging time increases. A softening curve is obtained from the correlation between Vickers hardness and the PIRMP. This curve can be used as a non-destructive method to evaluate the remanent life of turbine rotor steel.
Keywords
alternating perturbing magnetic field; reversible magnetic permeability; PIRMP; turbine rotor steel; remanent life;
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