Abstract: This paper is about using phased array ultrasonic testing method with special Cobra scanner to inspect small diameter circumference welding. This method complies with ASME B31 code, and is a kind of complete substitute method of X-ray inspection. After the experiment and on field testing, this method can test small diameter pipe with diameter 21 mm to 114 mm, and can access limit space. Because of the characteristic of curved element probe, curved probe testing result is better than linear probe on accuracy. This method can test both carbon steel and stainless steel. This method can do simulation before testing and can analyze accurately after the testing.