Automatic Ultransonic Test The large quantity of the high strength Q&T steel, SM570, was used in the Yongjong Grand Bridge to reduce dead load. The Q&T steel has lower fatigue strength so that lots of attention was paid to remove weld defects during fabrication and handling. To have high quality of the welding, the AUT system, which has been applied in Japan, was introduced to inspect of the corner weld of the lower chord. The weld defect and the level of penetration in the corner weld was inspected by the AUT system.