Letter 8077

Tin plating out on Titanium heat exchanger plates

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I recently replaced 316L SS heat exchanger plates with Titanium to over come pitting corrosion problems experienced with the 316L plates. The heat exchanger is actually functioning as an evaporator under vacuum. The solution being heated is a Tin electrolyte solution (methyl sulphonic acid), containing 20-25g/l of Sn2+ (stannous tin). After 1 week operation the exchanger was opened for inspection and we found a spongey tin deposit in between the first 60 plates.

We suspect that the reactions Ti-->Ti2+ + 2e- and Sn2+ + 2e---> Sn are occuring.

What I don't understand is if the Titanium plates are covered with an oxide layer how could this be occurring. Under the tin deposit the surafce of the titanium was a very colorful combo of blues and purples. Is this a result of a very thick layer of titanium oxide being deposited?

We recently discovered that the plates now have holes and we suspect it is due to the loss of titanium metal?

Can anyone out there enlight us on this problem??

Thanks,

Steve Van Smaalen
BHP Steel - Port Kembla, NSW Australia

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