What to do to avoid the error in the floating head design
27 Tubesheet loading conditions, longitudinal membrane stress
There is failure due to tube axial membrane stress, the tubes would buckle:
Increasing tube thickness (ex. 5.156 mm) helps remove all of the tube membrane stress errors but that might not be a solution from process/thermal design perspective as tube becomes too thick:
Another solution could be to reduce baffle spacing (example - reducing the spacing to 300 mm)
Overall it really depends on what approach the designer wants to adopt.