超声TOFD二次波检测技术在奥氏体不锈钢焊缝无损检测中的应用

由组织结构引起的声能衰减、散射、声束扭曲会使得奥氏体不锈钢焊缝的超声检测较为困难。分析了焊缝中超声波衰减及散射的各向异性特征及其影响因素,并提出了基于超声TOFD技术的二次波检测方法。通过调整探头间距改变焊缝目标区域的检测声束折射角,深入分析声束入射方向及晶粒生长方向对检测信号信噪比的影响。结果表明:检测波在奥氏体不锈钢焊缝中的传播呈现明显的各向异性特征;当检测声束与柱状晶生长方向成较小夹角时,可获得较高的检测信号信噪比。因此,当探头置于焊缝余高侧时,为获得较小的检测声束与柱状晶生长方向间的夹角,采用基于超声TOFD技术的二次波检测方法可提取焊缝中缺陷的衍射波特征信号。     

奥氏体不锈钢焊缝超声阵列检测方法

在焊接热循环作用下,奥氏体不锈钢焊缝内部呈粗大柱状晶组织,且其取向在焊缝不同区域呈各向异性.针对粗大柱状晶引起的超声波散射和晶粒取向不同导致的声束偏折等问题,进行奥氏体不锈钢焊缝超声阵列检测方法研究.针对超声阵列获得全矩阵数据,发展了一种基于时间反转算子分解的超声阵列信号去噪方法.利用射线追踪法,研究了各向异性介质中超声波传播路径确定方法,并将其应用于奥氏体不锈钢焊缝超声阵列全聚焦成像的声束偏折校正.开展了奥氏体不锈钢焊缝超声阵列检测试验研究.结果表明,基于时间反转算子分解方法可以很好剔除检测信号中的散射噪声,凸显特征回波信息,可将全聚焦成像的信噪比提高10 dB,而波束偏折校正则可以提高超声阵列全聚焦成像中缺陷定位的精度.     

基于超声波的升船机船厢现场组拼焊缝无损检测方法

为准确检测升船机船厢组拼焊缝的缺陷问题,提出基于超声波的升船机船厢现场组拼焊缝无损检测方法。选择CTS-20超声波探伤仪作为升船机船厢组拼焊缝的检测工具,在焊缝余高侧和根部侧均安装超声波探头,根据探头的信息采集结果,计算直通波、缺陷衍射波和底波的起波位置。通过分析检测声束方向及缺陷衍射波信噪比,描述声波传播特征。最后,分析超声波声束入射方向和柱状晶生长方向的夹角与探头中心距的关系,通过回波信号反馈回来的焊缝位置、深度、尺寸等信息,判断焊缝是否存在缺陷。试验结果表明,文中提出的检测方法能够凸显出不同缺陷类型回波信号在其对应频带上的分布差异,具有较高的焊缝缺陷检测率。     

奥氏体不锈钢厚板焊缝相控阵超声检测

枝状粗晶、各向异性引起声束偏移、强散射和高衰减,是奥氏体不锈钢焊缝UT难点。介绍用超声相控阵双矩阵探头检测厚板焊缝(50mm~120mm)的过程要领,包括实物试块的制作、人工靶体的设置、探头波型、频率、扫角的选定等。给出了检测配置和图像显示实例。可供此领域难题解析和信号评断借鉴。     

奥氏体不锈钢焊缝超声衍射时差法检测的有限元仿真及应用

基于有限元方法建立了奥氏体不锈钢焊缝超声衍射时差法(TOFD)检测过程的数值模型,结合试验方法分析了超声波与焊缝组织结构的相互作用机理,提出降低焊缝散射噪声干扰的探头布置方法。结果表明,有限元模型可模拟超声波在奥氏体不锈钢焊缝中出现的各向异性特征,包括声场扭曲、声能散射和衰减现象。结合检测试验证明,通过改变探头检测面,可降低焊缝组织结构对TOFD检测信号的不利影响。     

奥氏体不锈钢焊缝手工超声波TRL探头检测方法的探讨

奥氏体不锈钢焊缝因为具有粗大晶粒和各向异性,造成了超声波的散射和衰减严重,从而使超声波检测灵敏度和信噪比下降。文中选用单晶横波斜探头、单晶纵波斜探头和TRL探头(纵波一发一收斜探头)对奥氏体不锈钢焊缝的超声波检测进行了试验研究。试验结果表明, TRL探头的检测效果优于单晶纵波斜探头,单晶纵波斜探头优于单晶横波斜探头,为奥氏体不锈钢焊缝的超声波检测提供了一定的参考。     

各向异性焊缝相控阵超声检测楔块角度的优化设计

超声波在各向异性介质中传播时,超声衰减值和声速大小会随声波入射角度的变化而改变,因此针对各向异性焊缝相控阵超声检测的特点,提出了一种通过优化探头楔块角度来获得最佳入射角度的工艺方案。首先,利用电子背散射衍射法评价焊缝的显微结构,基于Silk模型建立了焊缝各向异性模型;其次,运用CIVA仿真软件计算不同楔块角度、不同检测距离对应的反射幅值;最后,对数据进行综合分析,确定最优化的楔块角度以获得最佳的反射信号幅值。运用优化设计方案对奥氏体不锈钢小径管对接焊缝试样进行数值仿真和检测试验,结果表明,通过使用角度优化后的探头楔块的相控阵检测仪,可以很好地实现奥氏体不锈钢的焊缝检测,使缺陷定位更加准确,为奥氏体不锈钢焊缝检测工艺优化提供了可行的技术方案。     

厚壁奥氏体焊缝超声波检测之探究

由于奥氏体焊缝中材料性能的各向异性和微观组织结构的不同,奥氏体焊缝的超声波检测是非常困难的。超声波在奥氏体焊缝中会沿金属结晶方向发生偏转,并在焊缝边界上发生散射。过去十年来,人们开发了多种模拟各向异性材料中声波传播的仿真工具。本文则以常规超声波检测方法为基础,将声线跟踪法和弹性动力学有限积分技术（EI、IT）相结合,应用于含晶间应力腐蚀裂纹的厚壁奥氏体焊缝中,其结果显示声线跟踪法和弹性动力学有限积分技术（肼）结合应用,有助于超声波检测参数的选取。     

激光-微束等离子弧复合焊接过程的结构负载声发射信号表征

采用脉冲YAG激光焊、微束等离子弧焊和激光-微束等离子弧复合焊对304不锈钢进行焊接试验,实时采集焊接过程中的结构负载声发射信号,研究声发射信号对焊接过程的表征. 结果表明,激光离焦量为-2 mm的激光-微束等离子弧复合焊接,热源复合效果更好,焊缝表现出更显著的复合热源焊接特征. 焊缝获得了更好的表面成形和熔深、熔宽. 热源复合效果更好的焊接过程,其声发射信号波形表现出更大振幅,且更为均匀,并与激光热源的周期性相符,呈现出明显的复合热源焊接周期性. 因此可以利用焊接过程检测到的结构负载声发射信号表征激光和微束等离子弧两种热源复合效果特征.     

奥氏体不锈钢点蚀缺陷的相控阵超声检测

奥氏体不锈钢母材晶粒粗大,焊缝组织为柱状晶,对超声波有强烈的散射衰减和扭曲作用。采用常规的超声检测技术难以对其进行有效检测,而相控阵超声检测技术具有检测效率高、精度高、实时成像的特点,为奥氏体不锈钢的检测提供了新的方法。利用相控阵超声检测技术对奥氏体不锈钢点蚀缺陷进行检测,验证了该技术的可行性。     

Ultrasonic array imaging through an anisotropic austenitic steel weld using an efficient ray-tracing algorithm

Ultrasonic inspection of austenitic welds is challenging due to their highly anisotropic and heterogeneous microstructure. The weld anisotropy causes a steering of the ultrasonic beam leading to a number of adverse effects upon ultrasonic array imagery, including defect mislocation and aberration of the defect response. A semi-analytical model to simulate degraded ultrasonic images due to propagation through an anisotropic austenitic weld is developed. Ray-tracing is performed using the A^⁎ path-finding algorithm and integrated into a semi-analytical beam-simulation and imaging routine to observe the impact of weld anisotropy on ultrasonic imaging. Representative anisotropy weld-maps are supplied by the MINA model of the welding process. A number of parametric studies are considered, including the magnitude and behaviour of defect mislocation and amplitude as the position of a fusion-face defect and the anisotropy distribution of a weld is varied, respectively. Furthermore, the use of the model to efficiently simulate and evaluate ultrasonic image degradation due to anisotropic austenitic welds during an inspection development process is discussed.     

Ultrasonic through-transmission characterization of thick fibre-reinforced composites

Thick composites pose a significant challenge to the ultrasonic nondestructive evaluation process due to the increased attenuation as well as the influence of material anisotropy. The physics of ultrasonic wave propagation in anisotropic material involves understanding such phenomena as beam skewing, material focusing/defocusing, unsymmetrical beam profiles, etc. This ultrasonic behaviour can be considered to be relatively insignificant in the nondestructive evaluation of thin anisotropic composite structures, but cannot be neglected in thick composites. In this paper, the ultrasonic characterization of thick glass-epoxy composites using an immersion through-transmission method employing a standard ultrasonic robot scanner system is discussed in detail. An inverse technique for computing material elastic constants from the acquired data is discussed. The experiment measures group velocity is a function of energy propagation angle (group angle), from which phase velocity is numerically computed as a function of phase angle. Then, the material constants are determined from phase velocity profiles using commercially available parameter identification software. Both uni-directional (five independent elastic constants) as well as cross-ply (nine independent elastic constants) were considered. Through-transmitted ultrasonic beam characteristics in thick composites are then analysed using feature extraction procedures and compared with the isotropic plexiglass structure.     

超声导波检测技术在电力系统的应用

介绍了超声导波激发的基本原理和导波的传播模式、分类以及导波在输电铁塔锚杆和角钢类型材检测、电站压力管道和小直径管子检测方面的应用。超声导波检测技术具有检验速度快、成本低等优点,能有效地提高检测效率,可广泛应用于电力系统的无损检测工作。     

基于视频定位的焊缝缺陷超声检测技术

研究了一种基于USB摄像头定位的焊缝缺陷手动超声检测系统,通过USB摄像头实时获得超声波探头相对于焊缝的平面二维位置,结合探头传感的焊缝缺陷深度信息,以三维投影成像方法表征缺陷三维信息,进而直观的对焊缝缺陷进行定位定性定量综合分析诊断,适用于在役焊接结构的现场检测.利用该系统对裂纹实际焊接缺陷进行了超声波无损检测.结果表明,采用该方法可以方便快捷,且较直观的给出焊缝缺陷的位置、大小、分布等特征,有助于对不同类焊接缺陷的定性识别.     

Ultrasonic and structural characterization of anisotropic austenitic stainless steel welds: Towards a higher reliability in ultrasonic non-destructive testing

The non-destructive testing of austenitic stainless steel welds of the primary coolant piping system is a significant problem for the nuclear industry. Ultrasonic techniques would be very helpful to detect, locate and size potential defects. Unfortunately, austenitic welds are coarse-grained, heterogeneous and anisotropic. This leads to aberration and scattering of the ultrasonic waves. In this paper, we present several experimental results of ultrasonic testing of two austenitic welds exhibiting high anisotropy. In order to explain the observed display of wave propagation phenomena such as beam deviation, we use finite element modeling. The modeling is associated with a complete characterization of the inspected welds. Two essential characteristics of the welds are determined: the average elastic constants of the weld and the grain orientations. The capability of the model is illustrated in different testing configurations. This work associating structural characterization and modeling shows that a better understanding of the phenomena of ultrasonic propagation should allow the interpretation and reliability of the industrial inspections of heterogeneous anisotropic welds to be improved.     

PE管超声检测试验

测量了PE管的纵横波声速及PE管热熔焊缝声衰减系数,确定了PE管材料的声学性能。采用小波域去噪理论去除噪声,提高了检测回波的信噪比。试验表明,超声检测方法适用于PE管热熔焊缝的焊接质量检测。     

A comparative evaluation of ultrasonic testing of AISI 316L welds made by shielded metal arc welding and gas tungsten arc welding processes

Ultrasonic testing of austenitic welds prepared by two different welding processes is studied in this paper. The two welding processes considered are shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) and the ultrasonic testing technique used is time-of-flight diffraction (ToFD). Identical artificial flaws were implanted in both welds during the welding process. Austenitic characteristics consisting of grain orientation distribution and anisotropy show that the GTAW specimen is more isotropic than the SMAW due to the orientation of its grains. Moreover, comparison of echo amplitudes shows higher attenuation for the weld prepared by the GTAW process. The specimens were examined by the ultrasonic ToFD technique under identical conditions. B-scan images obtained from ToFD measurements of the two welds indicate that inspection of the specimen prepared by the SMAW process is easier than the one made by the GTAW process due to higher scattering of waves in the latter. The measurements also showed that the probe positioning is very important in the detection of diffracted echoes when using the ToFD technique.     

基于空气耦合超声的激光焊缝质量评估

随着激光焊接技术在汽车及轨道交通上的广泛应用,对激光焊缝的无损检测技术要求越来越高. 针对3 mm以下的两层金属薄板激光焊缝为对象,探讨了空气耦合超声检测技术对激光焊缝检测的可能性. 利用数值解析和试验分析两种方法,在空气中对铝板激励兰姆(Lamb)波,通过Lamb波在激光焊缝试件中的传播模拟,分析了激光焊缝的宽度以及焊缝的良否对反射率及透射率的影响,解明了Lamb波在激光焊缝试件中的传播规律. 结果表明,可以利用Lamb波A0模式对激光焊缝的质量进行评估.     

3D ray tracing in austenite materials

In general, ultrasonic sound wave propagation through austerlitic (stainless steel) weld material cannot be predicted because of the anisotropic and inhomogeneous structure of the weld. To support NDT inspections, a ray tracing algorithm was developed to follow longitudinal, horizontal and vertical polarized shear wave propagation from the base material through the cladding in three dimensions. The algorithm was implemented in the ‘3D-Ray-SAFT' software package that allows experimental modelling, to visualize the rays in three-dimensions and to include reflections from arbitrarily placed flaws. The presented algorithm results that were experimentally validated are compared to similar, existing algorithms.