Are the weld joints between the heat exchange tubes and the tube sheet considered Class C welds?
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In 4.6.1 of GB151, as shown in the figure, there is a mark indicating a Class C weld joint at the connection between the floating head and the heat exchange tubes. Does this mark mean that the weld joint between the heat exchange tubes and the head is a Class C weld?
This C is the weld between the floating head flange and the spherical shell head
Then, since both the heat exchange tubes and the tube sheet are pressure-bearing components, can their connection welds be considered Class C welds?
Well, yes, generally this connector can only be inspected on the surface
The welding joint that connects this type of heat exchange tube to the tube sheet is an angled joint, classified as a Type C welding joint. Generally, only surface testing or interlayer testing is carried out on such joints; however, for some special heat exchangers, radiographic testing is also required for these angled joints. Radiographic testing can be performed by placing a radiation source inside the tube and attaching film to the surface of the tube sheet weld, using a hole pattern quality meter. The weld joints between tubes and tube sheets, as well as the internal hole welding configurations, are all of the butt-joint type; they cannot be subjected to non-destructive testing, and only surface inspection using an endoscope is possible. Generally, these joints cannot be repaired either. Therefore, very strict requirements exist regarding the structural design of such weld joints and the evaluation of welding processes.
The connection between the heat exchange tube and the tube sheet is not necessarily by welding; the standards provide no specific details on this.