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Do Stainless Steel and CLO2 Mix?

 

I am currently developing a conveyor system that will be used for the USPS to decontaminate mail. The conveyors will be washed "vigorously" with 10ppm chlorine/water solution. They will also be decontaminated with chlorine dioxide gas. I have seen varying reports on whether CLO2 is corrosive, so I ask you this. Will Stainless Steel (316) stand up to Chlorine Dioxide without corroding? Or shall I use another product?

Jerry Mosier
- Rochester, New York

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Stainless steel does not like chlorine. Whether or not your conveyor system will be attacked depends on a number of factors.

It is my understanding that chlorine dioxide needs high humidity to be effective. This could increase the risk of attack.

Length of exposure and frequency of application are factors. Will the conveyor be dry during exposure to the chlorine dioxide? Any residual moisture could increase the risk of attack significantly.

Good passivation after fabrication is essential if you are to resist corrosive attack. Electropolish would be even better. Periodic re-passivation will help.

I have seen 316 stainless steel rust because it was left in a room with an open container of hydrochloric acid for a few days. I mention this only to highlight the sensitivity of stainless to chlorine.

Given the available information and the likely sterilization cycles I think you will most probably be alright. If the sterilization is going to be very frequent and or long or the chlorine dioxide gas will be very strong I would consider using another alloy such as AL6XN.

Good luck,

John Holroyd
- Elkhorn, Wisconsin

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At 100% dry chlorine dioxide you will be fine, with any moisture you will not be in a good situation. I would call Allegheny Ludlum, Carpenter or similar company they will have data to support a proper material choice. Also if you don't have a good rinse you will have problems with the 10ppm chlorine, especially if you apply welding or have mechanical joints on the conveyor.

All the best,

Bradford Maas
- Northfield, Minnesota

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I work for a paper mill and we create ClO2 to bleach our paper. I am sure the percentage of ClO2 to H2O is stronger in some of our system, but we use all titanium lines and valves for handling the chemical. Some of our system is stainless, but this is only used for low percentage ClO2 (mostly H2O). I hope this helps.

Nicholas MacDonald
- Portland, Maine, USA
June 10, 2008