I believe you have both an erosion and corrosion problem.
The chlorides will pull the chrome out of the 316 SS.
If you have the capabilities, try placing a clean and weighed 316 sample of your part in your HCl solution at some elevated temperature, say 180F. Heat and move the solution with a...
With the high temperature and oxygen content, the alloying
components of the stainless will probably be attacked as will the copper tube ID. I suspect intergranular and crevice
corrosion will present problems.
depending on the temps involved, a granular carbon bed may be used to trap a portion of the chlorine to keep levels in
check. The bed will have to be replaced or recharged at some point. I suggest you analyze for chlorine/chlorides
before and after the carbon bed and replace when effluent levels...