Abstract: When the TOFD (Time of Flight Diffraction) method is used to detect the spherical tank, the steel segregation can cause interference to the TOFD atlas assessment. In this article, UT, TOFD and metallographic analysis are used to detect welds of shell plate of 1 000 m³ oxygen spherical tank, the detection results can be used to determine whether the detected TOFD display is caused by welding defects or by steel segregation.