Q. I am getting the following error messages:
equivalent stress in the tubes exceeded
longitudinal stresses in the tubes exceeded.
How do I solve these issues?
Ans: Please see the following wiki page:
In fixed tubesheet heat exchangers the differential expansion due to differential pressure, differential temperature or combination thereof may lead to excessive stress in the tubes, shell, tubesheet or tube-tubesheet weld joint.
One of the solutions to the problem is inclusion of an expansion joint as detailed in the link above.
If addition of an expansion joint does not eliminate the excessive tube stress, then user may have to consider the option of increasing the tube thickness which would usually eliminate the issue. However, please note that increasing tube thickness may affect the heat transfer rate and hence it is a decision to be made from not only mechanical but also the thermal design point of view.
The above suggestion is just for reference and one of the ways to resolve the said problem, while designing heat exchanger the engineer must use individual judgement and experience to arrive at the appropriate solution.