If you think about which surfaces are wetted (assuming liquids on both sides), it quickly becomes apparent that the tubesheet is wetted by both the tubeside and shellside fluids. I would say that it is both.
When we relaced tube sheets they were always part of the shell and when we replaced the tubes, the sheets were still part of the shell but then maybe I don't understand your question??
The tubesheet is a pressure boundary. When considering the shell side pressure and/or operating conditions, it is part of the shell pressure boundary. When considering the tube side pressure it is part of the tubeside boundary.
I was working on brittle fracture analysis of the exchanges.The case was shell side was esxposed to severe negative temperature at worst condition and while tube side was experiencing normal(not very negative) temperature.And I was checking individual component of the exchanger using API 579 to see which component are prone to brittle fracture.
And that is when I came across above question wether to conside Tubesheet on Shell side or Tube side while evaluatiing for brittle fracture?
But then I ended up considering the TS on the side(Shell or Tube) where it will experience the most negative temperature.And it seems to agree with many of yours input.
So thanks a lot againg for taking time for answering my (may be stupid) question?