Abstract: For inspection of high thickness welds greater than 100 mm in pressure equipment, using advanced ultrasonic TOFD(time-of-flight diffraction) technique accepted by ASME Code, the achieved flaw sensitivity and probability of detection are substantially better than the one by linear accelerator and manual ultrasonic methods. Comparison of flaw evaluation between the new technique and the traditional methods was drawn. The characteristics of the new technique in acceptance of the inspection results were illustrated with some practical examples.