Abstract: Aiming at the failure mechanism and crack defect characteristics of austenitic stainless steel small diameter pipe welds, a special ultrasonic phased array detection technology was developed, and the acceptance criteria and crack judgment method were determined. The field test was verified by 35 welds. The test results show that the ultrasonic phased array unqualified weld is basically consistent with the liquid surface penetration test on the inner surface.Ultrasonic phased array and ray detection are consistent with about 50% weld results, and ultrasonic phased array and ray detection have crack miss detection. Through theoretical analysis, experimental results analysis and statistical analysis of experimental data, it is concluded that ultrasonic phased array technology can effectively detect cracks caused by service; ultrasonic phased array technology detects crack defects in the opposite side of the probe during one-side scanning. Low rate is easy to miss detection. Ultrasonic phased array technology is easy to misjudge the defect properties for small cracks; the detection rate of ray-induced cracks is low. From the statistical analysis of the test results, the detection rate is lower than the ultrasonic phased array technology.