针对大直径厚壁管道对接焊缝根部缺陷的定性定量难点，提出了采用一纵一横双探头超声波衍射法进行检测的方法。该方法利用横波斜探头发射声束入射到管道根部，若根部存在缺陷，将产生衍射波。通过对置于管道焊缝表面的纵波直探头接收到的衍射波进行分析，可得到缺陷的深度。再结合斜探头测得的水平位置等数据以及衍射波形特征，可实现根部缺陷的定性和定量。试验总结出对裂纹、未焊透、未熔合、焊瘤、内凹以及错边六种缺陷的定性判据，并归纳出缺陷定性的分类流程。所介绍的检测方法对于大直径厚壁管道焊缝，尤其是只能进行单侧单面检测的管道焊缝具有实际检测应用价值。

Pointed to the difficulty of qualitative and quantitative testing for the welding testing of thick and great diameter pipe, a new method was put forward using the combination of a vertical and a shear wave probe. At first, the shear wave probe transmitted the ultrasonic wave to the welding root, and if there was a certain defect, it would produce the diffraction wave, and the wave would be received by the vertical probe located on the weld surface. Analyzing the depth of the greatest amplitude diffraction wave, combining the horizontal location of shear wave probe and the characteristics of diffraction wave, the qualitative and quantitative objection would realized. The qualitative judging methods for six kinds of defects such as crack, incomplete penetration, non-fusion, welding tumor, concave and wrong side, were concluded and the classification process was described. So introduced testing method has great application value for the welding testing of thick and great diameter pipe, especially for the welding testing which could be processed on single side and single surface tube.