How are the weld types of ASME spherical tanks and those of conventionally designed tanks in China classified? What are the differences between welding joints of classes A, B, C, and D?

Basically the same, with differences in the labeling for Category C

Most are the same; the differences lie in the classification for Category C. The following are the requirements specified in the national standard GB-150: ① The longitudinal joints in the cylindrical part of the vessel (with the exception of those in multi-layer wrapped vessel shells), the circumferential joints where the spherical head is connected to the cylinder, all weld joints in various types of convex heads, and the joints where embedded nozzles are connected to the vessel shell—all of these belong to Category A weld joints. Generally, it is the compressed longitudinal seam of the shell. ②The circumferential weld joints in the shell section, the joints where the small end of the conical head is connected to the pipe, and the joints where the long-neck flange is connected to the pipe all belong to Class B weld joints, except for those that have been designated as Class A, C, or D weld joints. The circumferential joints of the pressure vessel shell, the butt joints with the flanges, ③ the joints where the flat cover and tube sheet are connected to the cylinder in a non-butted manner, the joints where flanges are connected to the vessel shell and nozzles, the lap joints between the inner head and the cylinder, as well as the longitudinal joints between the layers of a multi-layer wrapped container, all belong to Class C welding joints. The fillet welds to the flanges ④, as well as the joints that connect components such as nozzles, manholes, flanges, and reinforcement rings to the shell, all fall under Category D welding joints, except for those that have been designated as Category A or B welding joints. The takeover is inserted into the pressurized shell; it meets US standard Class C. Both the flange-to-shell connection and the corner joints are of Class C

The butt welds connecting the nozzles to the flanges are classified as Category B, while ASME classifies all types of welds connecting nozzles to flanges as Category C.