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This study experimentally investigates the efficacy of TE11 mode microwaves in detecting bend-region cracks. Three types of bends with different dimensions were deployed in a 3 m piping system and then tested, with an axial or circumferential slit machined at different angular positions to simulate a crack. The TE11 mode microwaves were excited using self-designed TE11 mode microwave probes and utilised for crack detection. The experimental results show clear reflection peaks at the bend position, demonstrating the feasibility of applying TE11 mode microwaves in the detection of bend-region cracks. Furthermore, the peak location of reflection is in accordance with the angular position of the slit. The findings also indicate that the peak amplitude of reflection is affected by the factors of mode conversion of microwaves at a bend. In addition, the experimental results also manifest an excellent signal-to-noise ratio to both two types of slits, suggesting that the microwave NDT is a powerful tool for bend-region inspection. [ABSTRACT FROM AUTHOR]

This study investigated the effect of a bend on microwave NDT (non-destructive testing) applied for rapid pipe inspections. The factors affecting the mode conversion of microwaves due to a bend were deducted theoretically and verified through numerical simulation. Both theoretical and numerical results revealed that the mode conversion at a bend was actually determined by the frequency normalized by the cut-off frequency of an arbitrary mode (f / f c), the ratio of the curvature radius to the inner diameter of the pipe (r / D) and the bend angle (α). Subsequent experimental evaluations were performed using four groups of pipes with different inner diameters and five different bends. The effect of a bend was quantitatively evaluated by comparing the reflection signals from pipe wall thinning in a straight pipe with those in a bent pipe. The results showed that the presence of a bend led to a decrease in the reflection signal behind the bend, and the extent of decrease also depended on r / D and α of the bend. Furthermore, the length or the depth of the pipe wall thinning did not noticeably affect the decrease in reflection signal, when the bend's dimensions were certain. [ABSTRACT FROM AUTHOR]