Nondestructive Evaluation of Degraded 2.25Cr-1Mo Steel and Estimation of Nonlinear Acoustic Effect Using Bispectral Analysis

The nonlinear acoustic effect has been considered as an effective tool for the evaluation of material degradation. In this paper, the applicability of the nonlinear acoustic effect using bispectrum analysis to the evaluation of degraded 2.25Cr-1Mo steel is investigated. First, artificial aging was performed to simulate the microstructural degradation in 2.25Cr-1Mo steel arising from long time exposure at 538°C. Second, ultrasonic nonlinear parameter was quantitatively measured by bispectrum and power spectrum. The nonlinear acoustic parameter using bispectrum analysis was found to be clearly sensitive to material degradation.