Additional assessment for the heat exchange tubes and tube sheet: if the material of the tube sheet base layer changes, is a re-assessment required?
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Conduct an additional process evaluation for the heat exchange tube and tube sheet, where the base material of the tube sheet is Q345R with a Ti coating, and the material of the heat exchange tube is Ti； Currently, we are facing a situation where the base material of the tube sheet is S304, the cladding layer is Ti, and the heat exchange tubes are also made of Ti. Should we conduct an additional process evaluation for heat exchange tubes and tube sheets with a S304 base material? Please advise!
Personally, I don’t think it’s necessary; welding is done on the titanium layer, while the base layer does not participate in the welding process. The base sheet has no connection whatsoever with the welding material.
In the additional process evaluation rules for heat exchange tubes and tube sheets specified in NB/T47014, item D.4 lists the factors that require re-evaluation, but materials are not included among them; therefore, no re-evaluation is necessary.