Let me share my experience of Carbon Steel Fin Fan unit. The Unit was on Steam Turbine Condensing application. The client had corrosion problem within 16" from the outlet tube end.
We installed 20" long thin wall SS316 material sleeves to take care of the problem based on the...
I think Stainless Steel AL-6XN alloy which is a superaustenitic stainless steel is one of the best materials for Sodium Chloride (26%) and Sulfuric Acid (7%) contaminated environments.
Better check with Allegheny Ludium Corporation who developed AL6XN for further details