# Cathodic protection of tubes in Shell & Tube Heat Exchanger

Our $\ce{Cl2}$ liquifier is of the following type:

It is entirely made of mild steel (shell as well as tubes plus the connecting pipelines). At shell side there is Freon (R-12) with its refrigeration cycle (not shown here); at the tube side there is dried & compressed $\ce{Cl2}$ gas from compressor section (~2bar max). One must realise that drying of $\ce{Cl2}$ is done physically via passing it through packed glass wool columns & then washing it in $\ce{H2SO4}$ scrubbers & then again through glass wool columns...Compression is done via $\ce{H2SO4}$ liquid ring compressors.

Problem we face is excess corrosion of tubes which thus lose their thickness & may in time compromise...For instance every 2-3 weeks we open up this liquifier & wash the tubes (via high pressure demi/RO water) & we found quiet an amount of dark-green/brown sludge indicating ineffectiveness of our drying section. Lab test are yet to be done so that I can clearly say what this sludge is made of. From the WIKI what I understand the compounds of such colour can either be oxides or chlorides of Iron because sulphates of iron are yellow in colour...

In a nutshell what I can do is increase the number of drying towers or increase the number of glass wool columns, but the most active measure I am thinking of cathodic protection via impressed currents. Have any user here applied impressed currents to a S&T heat exchanger & how can it be done? I would love any literature on it.

As a side note our liquifier can be electrically isolated using gaskets & insulated teflon bolts on any flange fitting.