This discussion is a lit bit confusing, any way, this is my contribution: On CDU%B4s overhead distillation units, to avoid corrosion, first one has to act on operating windows and process key variables. If chemical corrosion mitigations processes don’t work, ok, you can go to others process such as installing tube inserts. Tube inserts are good for corrosion erosion problems in exchangers and air coolers but also present some disadvantages. If the problem is mainly erosion the disadvantage of tube inserts ferrules is that at the end of the ferrule you will get an erosion corrosion ring grove, and soon or later a rupture. When deciding to install tube ferrules, one has to be careful, the sustainable option is to install full-length tube liners inserts. Tube liners material is another discussion dear Mark Mor! On overhead CDU%B4s units you don’t have temperatures of 450ºC. Regards Luis Marques