Nondestructive Evaluation of Multiply Connected Electrical Arc Furnace Graphite Rod Electrodes

The low quality of graphite electrodes in a small electrical arc furnace causes many problems on furnace operation. High temperature and erosion at the remote electrode tip, and defects in the electrode increase the probability of electrode failure due to ageing phenomena such as thermal stress cracking. Most measurement techniques cannot determine the electrode quality under such conditions as the high temperature is highly destructive to the device. Nondestructive sensing techniques such as ultrasonics can possibly be used. Experimental studies on the feasibility of using mechanically connected and chemically bonded graphite rod electrodes as a sensing medium for an ultrasonic signal are performed. Graphite rod porosity and defects are inspected using ultrasonic, infrared, and Real-Time Neutron Radiography nondestructive inspection techniques. The acoustic characteristics of the graphite rods are determined, and the soundwave velocity of the graphite rods is measured to be 2529.4 m/s. Ultrasonic frequencies from 60.0 kHz to 10.0 MHz are studied. The optimum ultrasonic frequency for propagation through graphite rods, hence quality inspection, are 500.0 kHz and 1.0 MHz. The effect of electrode length and the number of mechanical joints on the operating ultrasonic frequency are discussed in detail.