Metal finishing Q&As since 1989

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How corrosion resistant is 304 for pond or lake water?

I'm thinking of purchasing a gravity-drained water filter where the housing is made out of 304 SS. The water filter will be used 1-3 times per day to filter lake or pond water into drinking water. How long can I expect the housing to last before corrosion becomes a problem?

Caroline Worsham
- Seattle, Washington, USA
May 21, 2008

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It all depends on the composition of your feedstock water. I would avoid 304 stainless if there is much chloride present, otherwise it should be OK

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
May 27, 2008

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May 29, 2008

Hi Caroline,

If you can drink the water, then the chloride content will be OK. It becomes a problem at higher concentrations, higher temperatures, and when the stainless steel is stressed by a mechanical load.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

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Bill, I'm not concerned about the water Caroline wants to drink, I'm concerned about the chloride level in the water she wants to process into drinking water. Chloride can be removed from the water by numerous "filtration" processes, but if the raw feedstock is high in chloride, once it gets in contact with the stainless steel, it will attack it.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
June 3, 2008

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June 4, 2008

Hi Trevor,

I guess it depends largely on interpretation of the word "filter". I see that as removing suspended solids, not as an ion-exchange or ion-removal (demineralising) process. So the water would have the same chemistry on the way in as it does on the way out. Maybe Caroline meant more by "filter" than my understanding of the term.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

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Bill,
I am going on the basis that Caroline wants to drink lake or pond water after removing any harmful contaminants. I am also using "filter" in the broadest sense, namely to remove these contaminants. Unless the lake or pond water is shown to be pretty pure and free of pollutants, I would be unhappy about drinking unprocessed water. I also note she lives in Seattle, which is a major city close to the ocean, so the chances of salt (sodium chloride)and other nasties being in the water will be pretty good. I have therefore extrapolated her term "filter" to include the removal of high levels of chloride to make the water drinkable; as you so correctly say, this could include (in my terms) ion exchange and ion removal. I agree that conventional terminology would limit "filter" to the removal of particulates, but this is not made clear here. Perhaps Caroline can enlighten us on exactly what she does want to do and what she is treating!

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
June 9, 2008