Assessment of creep damage in 2.25 Cr-1 Mo steel by electromagnetic acoustic resonance

摘要

A study was made on the performance of a novel EMAR (Electromagnetic Acoustic Resonance) technique for assessing creep damage in 2.25Cr-1Mo steel. The steel was exposed to a temperature of 923 K and put under various stress. The EMAR technique featured the use of two non-contacting electromagnetic acoustic transducers (EMAT) for test samples with different configurations. Ultrasonic velocity was obtained from resonant frequency and attenuation coefficient from ring down curves at resonance. One EMAT was a bulk wave type for measuring the frequency dependence of shear-wave attenuation of sample plates. The other was an axial-shear-wave type for detecting attenuation changes of shear waves traveling in the circumferential direction of cylindrical samples. It was found that attenuation was more sensitive to damage accumulation than was resonant frequency, reaching a ten-fold value (as compared to the initial attenuation value) when approaching a rupture. The frequency dependence of the attenuation also showed a remarkable increase with damage. All in all, research results indicated that the EMAR technique had a great potential of being used for practical nondestructive/non-contact damage monitoring. The EMAR technique was proven to be capable of sensing the evolution of attenuation, as well as providing diagnostic data on damage for predicting the creep life of 2.25Cr-1Mo steel.