For tubesheet integral with shell/channel, if the shell/channel stresses exceeds the allowable limit the code suggests to increase the tubesheet thickness(as one of the option) how does this helps?

You are looking at the stress at the junction of the tubesheet and the integral cylinder. So, if you increase the tubesheet thickness it reduces the stress at the junction.

But depending upon your case, a better option might be to try Elastic-plastic iteration.

Dear friends

I would like to add further add to Mr.Mandeep Singh's reply that increasing the tubesheet thickness result in decreased deformation (deflection or slope) at the junction and thus the resulting shear force / bending moment (arising out of compatibility consideration) decreases. That is why the shell stress in the junction decreases.

With regards

Thanks for the explanation.

Thank you sir for answering the query.