Exchanger expansion joint material / tube material

[Nikk5]

Hi group,

I have a particular situation with an exchanger, described as follows:

It is an exchanger (shell tube type) with fixed tube sheets and expansion joint in the shell.

Original design included CS shell with an expansion joint, tubes and tube sheets of the same material (SS 316).
the CS thermal expansion coeff is < than the exp joint, tubes and tube sheets.

Situation: Due to internal corrosion of the 316 SS tubes, a material upgrade is needed.
The upgrade must be a Ni-Mo alloy.

The problem is that Ni-Mo alloys have lower thermal expansion coefficient than carbon steel (CS)

If the replacement of the tubes is performed without replacing the SS-316 tube sheets and expansion joints: could it be an issue in the future operation due to different thermal expansions in the original design ?. (In this case there is no need to replace the 316 tube sheets or expansion joint for corrosion, only the tubes are affected by localized pitting).

Thanks for your comments,
Nikk5

 

[SnTMan]

Nikk5 the proposed material combination will need to be evaluated per Part UHX or similar calculations for fixed-tubesheet exchangers to insure the stresses in the tubes, tube-ts joint, shell, and expansion joint are acceptable for each ooperating case.

Regards,

Mike