Abstract: According to the principle of director digital panel radiography (DR) technique and ultrasonic phased array (PA) technique, the difference between these two new techniques can be obtained by comparing the typical defects of several different sizes of small diameter pipe welds. It can be concluded that DR technique and PA technique can detect the relevant defects on the whole, whereas the defect length given by PA was slightly oversized. As the PA technique is characteristic of 3D imaging, so its image display of defect can give more information. In addition to the length of the defect, the PA image also shows the amplitude of the reference sensitivity, the height of the defect, and it can achieve 3D dynamic imaging through setting the weld groove parameters, thus resulting in more intuitive display of defect location. On the other hand, the DR technique is to form more intuitive defect shape, and is easier to qualify the defect.