Abstract: In the conventional design of welding structures for header end caps, there are differences in welding seam detection between butt type and bottle cap type header end cap structures. This paper used phased array ultrasonic testing technology to inspect the welding seam of the header end cover containing artificially simulated defects, and compares it with radiographic testing and ultrasonic testing. The experimental results show that phased array ultrasonic testing technology has high reliability in identifying common defects such as porosity and lack of fusion in the welding seams of butt joint and bottle cap type header end caps and can be used as a complementary test method.