利用超声波常规反射法斜探头检测自动弧焊厚壁联箱窄间隙对接焊缝时发现，在其周向区域、一定深度区间内均存在当量不等的断续反射波信号，反射波水平位置均处于焊缝中心。采用超声波衍射时差法(TOFD)检测，检测分析并确定了该反射波信号为对接焊缝中存在的密集裂纹缺陷。检测结果表明，利用超声波反射法检测结合超声波TOFD检测，能有效地检测出自动弧焊厚壁联箱窄间隙对接焊缝中的危险缺陷。

On using the conventional ultrasonic reflection angle probe to detect automatic arc welding thick-walled narrow gap butt weld, it was found that there were some intermittent wave signals in the circumferential region and in certain depth interval, and the reflected waves being in horizontal position in the weld center. Ultrasonic TOFD inspection methods were employed for the detection analysis and it was found that the reflected wave signals were due to the dense crack defects in butt weld. The test results show that, ultrasonic TOFD testing combined with detection by ultrasonic method, can effectively detect dangerous defects of automatic arc welding thick-walled narrow gap butt weld.