Test Materials and Treatment

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1. Why is NDT applied to Electrical Arc Furnace graphite electrodes? A graphite electrode is normally moving into the arc furnace when the part of electrode tip was consumed or cracked during the operation. The electrodes must be periodically fed into the fur- nace, and additional material need to be added to the existing electrodes. 2. What NDT methods are used in the present publication? A sound pulse The pulse echo RTNR method 3. What are the specific objectives of each of these methods? Ultrasonic techniques have been used for thickness measurement of high porosity carbon brick from the outside of a blast furnace bosh area using the pulse-echo technique. A sound pulse was sent through the carbon brick to the brick-gas or brick-liquid metal interface and reflects proportional to the acoustic impedance between the two materials.The RTNR system examines each graphite rod and each mechanically bonded joint for large scale voids (less than 1 mm). 4. Why do the autors use different ultrasonic frequencies to inspect the electrodes? The optimum frequencies for ultrasonic propagation through graphite rods are 500.0 kHz and 1.0 MHz. Higher frequencies of 10.0 MHz and lower frequencies of 60.0 kHz do not produce good soundwave propagations. 5. How is porosity affected by rod diameter? And, consequently, how is ultrasonic wave attenuation affected by rod diameter? Porosity of a material usually contributes to the attenuation of ultrasonic waves. An attenuation effect is present even for low velocity waves. The porosity of several graphite rods is investigated to determine the ultrasonic soundwave transmission characteristics for each rod. The pulse echo method determines the compactness of the rods as the reflected signal strength is most important to the present application. 5.08 cm diameter graphite rods consistently have better soundwave

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