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Why Is Dimineralized Water Corrosive?

why dm water is corrosive?

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#1 Araboni

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Posted 28 July 2012 - 03:41 AM

dear all
as most DM water tanks/drums that I have ever seen in different industries are made from SS , does anybody know exactly why DM water is Corrosive?

#2 Art Montemayor

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Posted 28 July 2012 - 04:02 AM

Araboni:

Dimineralized Water is NOT corrosive. Let's agree on that fact. However, contaminated DM water IS corrosive - especially if contaminated with dissolved oxygen or carbon dioxide.

If oxygen is present, you get one form of corrosion: rust (or iron oxidation). If carbon dioxide is present, you get acidic attack on the steel with resulting acid etching of the steel. Both types are corrosive.

If your DM is stripped of all dissolved gases and is truly pure H2O, then you should have no corrosion. It is the contaminants that give problems - not the water.

#3 Araboni

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Posted 28 July 2012 - 04:14 AM

Dear Art
Really thank you for prompt reply. The spec of DM water available at our company is given herein after, and this DM water is coming from an RO/polisher package. Could I consider the MOC of our new facilities (pipings, tanks, etc.) which may be in contact with DM water , Carbon Steel ?

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#4 ankur2061

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Posted 28 July 2012 - 08:04 AM

Araboni,

Another reason that DM water is more agressive in terms of corrosion to carbon steel is that it contains almost no calcium or magnesium. Presence of calcium or magnesium in water tends to form a passive film of calcium or magnesium salts on the metal surface which to some extent protects the metal surface from corrosion. DM water lacking these salts is thus more agressive to carbon steel

Also note that DM water is not acidic (pH 5.2) at all as shown in your specification. DM water is always supposed to be slightly basic with the pH value ranging from 7.2 to 7.8 for on-specification DM water. The range you have provided for pH (5.2 to 8.8) is not something that is normally observed in DM water produced from a well designed, operated and maintained DM water plant.

Regards,
Ankur.

#5 Steve Hall

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Posted 28 July 2012 - 12:36 PM

Recognize, too, that the ironcorrosion product (ferrous hydroxide and ferric hydroxide) may adversely impact the acceptance criteria for the DM water. In the pharmaceutical industry, where deionized water is often characterized by its conductivity, any electrochemical reaction increases conductivity. The deionized water is considered to be highly aggressive (probably due to oxygen content per Art's comment) and is generally piped in 316L stainless steel, PVDF, polypropylene, or PVC. Stainless steel components are monitored for the formation of rouge, which is itself a corrosion product that occurs even when the passivation layer is intact.

#6 S.Chittibabu

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Posted 31 July 2012 - 02:43 AM

DM water when strored is to be protected from atmospheric contact since CO2 dissolves in DM water and becomes acidic. Hence the DM water tank has CO2 trap in the vent line. Normally morpholine is used to make the pH neutral where CO2 trap is not provided.

Edited by S.Chittibabu, 31 July 2012 - 02:43 AM.





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