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Corrosion detection in welds and heat-affected zones using ultrasonic Lamb waves

机译:超声波Lamb波检测焊缝和热影响区的腐蚀

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Measurements are reported on the amplitude of ultrasonic Lamb waves reflected from a single 20 mm-diameter flat-bottomed hole located adjacent to the weld of a 6 mm-thick butt welded steel plate. The hole was introduced to simulate the presence of corrosion defects in the heat-affected zone, and served to assess the suitability of using the fundamental S_0 Lamb waves as a means for remote detection of corrosion in fluid-filled storage tanks. Measurements were made using a prototype, omnidirectional multi-element transducer developed at Imperial College, and also using a single edge-mounted transducer. Detection of a hole was only possible when using the plate tester at oblique incidence angles, because of the inability to discriminate weld echoes from those due to the hole at normal or near-normal incidence. Detection of holes was also limited to those with a minimum depth of approximately 3 mm by the presence of coherent background noise. Measurements using a single edge-mounted transducer demonstrated that preferential waveguide propagation of the S_0 mode occurred along the weld, in a manner coined 'weld-guided waves'. This permitted easy detection of a 2 mm deep-hole located adjacent to the weld at a distance of 1 m from the transducer. It is likely that a practical surface-mounted transducer based on the S_0 waveguide mode of operation could be developed for the inspection of corrosion defects within the heat-affected zone of fluid-filled tanks. It is probable that such a device would have a range of many metres, be simple in construction, and that the method would be relatively unaffected by the presence of fluid and inherently sensitive because of the suppression of other propagation modes.
机译:据报道,测量了从与20 mm厚的对接焊接钢板相邻的20 mm直径的平底孔反射的超声波Lamb波的幅度。引入该孔是为了模拟热影响区中腐蚀缺陷的存在,并用于评估使用基本S_0 Lamb波作为远程检测充满流体的储罐中腐蚀的方法的适用性。测量是使用帝国理工学院开发的原型全向多元素传感器进行的,还使用了单边安装的传感器。仅当以斜入射角使用平板测试仪时才可能检测到孔,因为无法将焊缝回波与法向或接近法向入射的回波区别开。由于存在相干背景噪声,对孔的检测也仅限于最小深度约为3 mm的孔。使用单个边缘安装式换能器进行的测量表明,S_0模式的优先波导传播沿焊缝发生,形成方式为“焊接导波”。这使得可以轻松检测到距换能器1 m处与焊缝相邻的2 mm深孔。可能会开发出一种基于S_0波导工作模式的实用表面安装式换能器,以检查充液罐热影响区内的腐蚀缺陷。这种装置很可能具有许多米的范围,构造简单,并且由于抑制了其他传播模式,该方法将相对不受流体的影响并且固有地敏感。

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