水利工程中金属焊缝缺陷的超声检测方法比较研究

Comparative study of ultrasonic detection methods for metal weld defects in hydraulic engineering

为研究基于超声的无损探伤方法在水利工程金属结构焊缝缺陷识别中的应用,利用常规超声检测技术、超声相控阵技术、衍射时差法(Time of Flight Diffraction, TOFD)超声检测技术对水利工程金属结构焊接试块缺陷进行识别,分析了各种缺陷在超声无损探伤技术中的特征显示。研究结果表明:常规超声检测技术、TOFD检测技术均能对各种缺陷实现信号显示,超声相控阵检测技术对气孔和横向裂纹的显示不够明显,但对其它缺陷的检出效果较为明显;常规超声检测技术对操作人员的要求较高,对缺陷的定性困难,精度不高;TOFD检测结果中气孔和横向裂纹的显示呈现出一种特殊的弧形,有一定高度的内部裂纹和未熔合的信号由上下尖端衍射波组成,根部未焊透上下尖端信号不够明显;相控阵检测结果直观,可以较精确地测量缺陷的埋藏深度、自身高度、长度等,但在扫查点状缺陷或者与超声声束平行的裂纹缺陷时,检出率极低。

In order to study the application of ultrasonic nondestructive(NDT) detection in weld defects identification of metal structures in hydraulic engineering, three methods: conventional ultrasonic inspection method, ultrasonic phased array technology and time of flight diffraction(TOFD) technique, are used to identify the defects in welded samples of metal structures. The characteristics of various defects detected by the three methods are analyzed. The results indicate that the conventional ultrasonic inspection method and TOFD technique can display a variety of defect signals;the ultrasonic phased array technology can effectively detect these defects except porosity and transverse cracks;the conventional ultrasonic inspection method is difficult to determine the shape of defect;in TOFD inspection, the porosity and transverse cracks show special arcs, the signals of the internal crack with a certain height and the incomplete fusion are composed of diffraction waves at the up and down ends, and the diffraction waves at the up and down ends of incomplete root penetration are not obvious. The detection results of ultrasonic phased array technology are intuitive and can be used to measure burial depth, self height and the length of defects, however, the detection rate is very low when scanning spot defects or crack defects parallel to ultrasonic beam.