CP in Demineralized water

[Chadarchie]

Has anyone ever dealt with cathodic protection in demineralized water with resistivity up to 6.25 million! Can anyone direct me to any reference regarding the corrosivity of this environment. From what I have been told the water is so starved of Fe that it will be aggressive in dissolving steel. I would think that there should be a different CP criteria (e.g. CP levels/current requirements etc.) to prevent this from happening.

The tank is internally coated which means I have to watch CP gradient so I don't blow the coating off.

Any input is appreciated. Thanks.

 

[corrosionman]

chadarchie If the tank is coated why do you need a CP system ?
regards

 

[Chadarchie]

Because of holidays.

 

[unclesyd]

I would be leery of a CP system in this application because of the resistivity of the DI water. AS you state you easily cause coating failure. I can’t remember every having a discussion of such an application of CP.
All our pure water systems used either in SS or Al as the material of construction after the
deionizers .

This website list several sources of information on the protection of coatings.

Click on “cathodic protection”

http://www.corrpro.com/Products/Index.htm

http://www.corrpro.com/Products/prodcathod.htm

 

[Skogsgurra]

Chadarchie,

There was a discussion about corrosion in ultra pure water in thread338-93016.

"moltenmetal" (Chemical) Apr 22, 2004 says:

"Interesting problem. To my knowledge, SiC is not attacked by water, steam or condensate, to quite high temperatures. I know of no reason that removing the last few ppm of impurities from the water should matter. I can't comment on your induced current theory without knowing the particulars, though it's clear that you can dissolve many things if you provide enough electrochemical driving force.

Ultrapure water is also, to my knowledge, NOT corrosive toward stainless steels. There may be issues with minor quantities of metal ions released from stainless steels which may result in contamination of the ultrapure water, particularly soon after the material is brought into service, but that's not the same as saying that ultrapure water will aggressively corrode the stainless steel. It's this common misconception that your colleagues are probably repeating. Hot, oxygenated pure water IS aggressive toward copper and brasses (particularly in areas of high local velocity), but in closed deoxygenated systems both of these materials also stand up quite well- regardless of how pure the "pure" water is." (End of qoute)

I have also heard about ultra-pure water being "hungry" for iron, but I think that it is an engineering (or rather pipe-bender*) myth.

*Our word for plumber

 

[EdStainless]

You could use CP in DI water, but it would end up 'not DI', you would put so many metal ions into it.
Well cleaned and passivated SS holds up very well, thank you. Coated CS tanks are often used. You must just inspect them and if the rusting gets too serious then you clean and spot coat.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm