groags
Chemical
- Jul 28, 2003
- 6
Hi,
I will ask the Chemical Engineers the same question I asked the Materials Engineers and hopefully someone might have some knowledge.
I have a Grade 17 Titanium Autoclave that needs to be temporarily decommissioned for 3 months. It is currently in service for a high pressure sulphuric acid leach in the presence of chlorides. A fairly severe service which it handles well. However we do get chloride crevice corrosion.
We intend to mechanically descale the autoclave, the scale is a Iron/Sodium Oxide. After cleaning we are concerned about what to do next to limit corrosion for the 3 month period. You might say that at ambient conditions any corrosion would be negligible so why bother ? Given the value of the Autoclave however I dont believe we should take that risk. My question is does anybody have an opinion on how to leave valuable process equipment of this type so it can be safely recommissioned at a later date?
The one Materials Engineer that replied stated that in his experience cleaning titanium vessels with water and letting them sit is good enough. What about the Iron layer that will be left on the titanium after descaling. Surely that will continue to corrode the titanium, especially in the crevices, albeit at a slower rate?
My thinking is that Nitric acid should be used to pickle the titanium to remove any contaminants and allow the Titanium Dioxide layer to reform. Then the vessel should be cleaned with pure water to remove acid and then filled with an inert gas such as Nitrogen and left to sit. This seems like overkill but with such valuable equipment should it be the standard ?
I know that that other metals need to be pickled/passivated but even though titanium has excellent corrosion protection even it must need treatment of some kind to prevent any kind of corrosion ?
Hopefully the Chemical/Process people might be able to shed some light on this potential problem for me. I would be interested to know what people think.
Regards,
Ronan
I will ask the Chemical Engineers the same question I asked the Materials Engineers and hopefully someone might have some knowledge.
I have a Grade 17 Titanium Autoclave that needs to be temporarily decommissioned for 3 months. It is currently in service for a high pressure sulphuric acid leach in the presence of chlorides. A fairly severe service which it handles well. However we do get chloride crevice corrosion.
We intend to mechanically descale the autoclave, the scale is a Iron/Sodium Oxide. After cleaning we are concerned about what to do next to limit corrosion for the 3 month period. You might say that at ambient conditions any corrosion would be negligible so why bother ? Given the value of the Autoclave however I dont believe we should take that risk. My question is does anybody have an opinion on how to leave valuable process equipment of this type so it can be safely recommissioned at a later date?
The one Materials Engineer that replied stated that in his experience cleaning titanium vessels with water and letting them sit is good enough. What about the Iron layer that will be left on the titanium after descaling. Surely that will continue to corrode the titanium, especially in the crevices, albeit at a slower rate?
My thinking is that Nitric acid should be used to pickle the titanium to remove any contaminants and allow the Titanium Dioxide layer to reform. Then the vessel should be cleaned with pure water to remove acid and then filled with an inert gas such as Nitrogen and left to sit. This seems like overkill but with such valuable equipment should it be the standard ?
I know that that other metals need to be pickled/passivated but even though titanium has excellent corrosion protection even it must need treatment of some kind to prevent any kind of corrosion ?
Hopefully the Chemical/Process people might be able to shed some light on this potential problem for me. I would be interested to know what people think.
Regards,
Ronan
