The paper highlights methods of nondestructive testing and their use to diagnose solid media of graphite electrodes applied in steel furnaces for identification of different defects. The main focus of the paper is to consider the methods of eddy-current testing of graphite electrodes. Besides, it presents the possibility of increasing the sensitivity of the method and localization of the place of potential damage. The practical importance of the paper includes simulation modelling of electromagnetic processes with further description of detailed results and conclusions.