小口径薄壁管中纵向缺陷的周向超声导波检测

对于小口径薄壁管的检测，通常采用超声水浸聚焦法。该方法灵敏度高、可靠性好，但不适于原位探伤，且检测速度慢、设备昂贵。为此提出了基于周向导波技术的检测方法。在实际检测过程中，观测到一组特殊回波序列，查明了这种回波是由侧向耦合剂液面反射产生，其对保证检测可靠性具有重要价值。通过数值计算，得到管材中周向导波的频散曲线，确定了导波模态，并计算了该导波的位移分布。试验及计算结果表明，该周向导波的能量主要集中在管材的外表面附近，可有效地进行小口径薄壁管的原位探伤，弥补了水浸聚焦法的不足。

Circumferential Guided Waves Testing for Longitudinal Defects in Small Tubes

The common method for detecting small tubes is the focused beam immersion method. This method is highly sensitive and reliable, but not fit for in-situ inspection, due to low speed and high cost. To solve these problems, the method based on circumferential guided waves technique was proposed. In actual testing process, a series of special echoes, which were valuable for guaranteeing the reliability of the tests. It verified that these echoes were reflected waves by the lateral surface of couplant. The velocity dispersion curves for the guided waves in tube walls were calculated numerically and then the modes of the guided waves were determined, and the displacement profiles across the wall thickness were obtained similarly. The experiment and caculation results showed that large percent energy of the guided wave was concentrated near the outer surface of the tube, and it was useful for in-situ inspection of small tubes as a compliment to the focused beam immersion method.