Tube-to-tube impact wear damage mechanism and nonlinear ultrasonic detection method of alloy 690 tubes

Abstract

Tube-to-tube impact wear is one of the prime reasons that cause the failure of alloy 690 tubes in nuclear steam generators. Therefore, it is of great importance to study the tube-to-tube impact wear damage mechanism and damage detection method of alloy 690 tubes. In this paper, the tube-to-tube impact wear experiments are conducted on alloy 690 tubes under different impact loads and cycle numbers. The impact wear damage mechanism of alloy 690 tubes is revealed by analyzing the macro and micro morphologies as well as metallographic structures of the wear scar. A nonlinear ultrasonic wave mixing (NUWM) method is proposed for damage detection of alloy 690 tubes. A detection device is developed to implement the NUWM method. A nonlinear modulation index is used to assess the damage degree of alloy 690 tubes. Experimental results indicate that, for an impact load lower than 100 N and a cycle number smaller than 2 × 105, the tube damage is mainly in forms of the surface plastic deformation and delamination. For a higher impact load or a larger cycle number, the fatigue cracking is the main tube damage mode. With increasing the impact load or cycle number, the tube damage degree increases, leading to an increase of the nonlinear modulation index. Therefore, the NUWM method is effective for detecting and assessing the damage of alloy 690 tubes.