焊接非破坏性测试 - 超声波测试 - 飞行时间衍射技术（Tofd）的使用

[中文适用范围]： 本文件规定了飞行时间衍射 (TOFD) 技术在最小厚度 6 毫米金属材料熔焊接头半自动或全自动超声波检测中的应用。 它适用于板材、管道和容器中简单几何形状的全熔透焊接接头，其中焊缝和母材均为低合金碳钢。 在指定且适当的情况下，TOFD 还可用于表现出低超声波衰减（尤其是由于散射而导致的）的其他类型的材料。 在本文件中指定与材料相关的超声波参数的情况下，它们基于纵波声速为（5920±50）m/s、横波声速为（3255±30）m/s的钢。 当以不同的速度测试材料时，有必要考虑这一事实。 本文件参考了 ISO 16828，并就 TOFD 在熔焊接头中的不连续性检测、定位、尺寸确定和表征方面的具体功能和限制提供了指导。 TOFD 可以作为独立方法使用，也可以与其他无损检测 (NDT) 方法或技术结合使用，用于制造检查和在役检查。 本文件根据 ISO 17635 指定了四个测试级别（A、B、C、D），并对应于不断提高的测试可靠性级别。 提供了有关测试级别选择的指南。 本文件允许评估 TOFD 指示以用于验收目的。 该评估基于对生成的 TOFD 图像中传输、反射和衍射超声波信号的评估。 本文件不包括不连续性的可接受水平。 [外文原描述]： This document specifies the application of the time-of-flight diffraction (TOFD) technique to the semi- or fully automated ultrasonic testing of fusion-welded joints in metallic materials of minimum thickness 6 mm. It applies to full penetration welded joints of simple geometry in plates, pipes, and vessels, where both the weld and the parent material are low-alloyed carbon steel. Where specified and appropriate, TOFD can also be used on other types of materials that exhibit low ultrasonic attenuation (especially that due to scatter). Where material-dependent ultrasonic parameters are specified in this document, they are based on steels having a sound velocity of (5 920 ± 50) m/s for longitudinal waves and (3 255 ± 30) m/s for transverse waves. It is necessary to take this fact into account when testing materials with a different velocity. This document makes reference to ISO 16828 and provides guidance on the specific capabilities and limitations of TOFD for the detection, location, sizing and characterization of discontinuities in fusion-welded joints. TOFD can be used as a stand-alone method or in combination with other non-destructive testing (NDT) methods or techniques, for manufacturing inspection, and for in-service inspection. This document specifies four testing levels (A, B, C, D) in accordance with ISO 17635 and corresponding to an increasing level of testing reliability. Guidance on the selection of testing levels is provided. This document permits assessment of TOFD indications for acceptance purposes. This assessment is based on the evaluation of transmitted, reflected and diffracted ultrasonic signals within a generated TOFD image. This document does not include acceptance levels for discontinuities.