Thanks Dorin for that detailed explanation. Nowadays, the Elastic Plastic analysis is becoming common to overcome this requirement in ASME VIII Div.2 to consider restrain free end displacements (thermal piping loads) as primary membrane stress in case the shell/nozzle fails with this criteria, if I remember right there is a 2.4 factor on load for this EP Analysis. But I think from piping, the factor of safety is still sufficient provided good engineering design practice is followed. As stated above if potential vibration is an issue and an axial restraint is really required while allowing for thermal expansion then snubber might be a good solution.

Any other opinion is greatly appreciated and just correct me in case I have made wrong statement.

Cheers!!!