Passivate equipment...

[Bilsch]

CitriSurf might be capable of oxidizing the chromium because it contains other things as a proprietary mix but citric acid does not. No matter though since atmospheric O2 will finish the job.

Also I'm happy to see that we as a forum have moved away from the dogma that starsan passivates.

 

[CodeSection]

Is there consensus on how many days one must allow to air dry after using citric acid?

 

[day_trippr]

"Consensus is hard to come by in this territory, pardner"
I fried my IC yesterday, and I'll be brewing in the morning, so I'm gonna go with "at least 24 hours"...

Cheers!

 

[RPh_Guy]

Is there consensus on how many days one must allow to air dry after using citric acid?

I've seen opinions range from immediately to several weeks.

My opinion is that since there seems to be no official recommendations for a required timeframe (despite widespread use in various industries), that it's probably not hugely important.

 

[Vale71]

- The oxide layer will form passively with air exposure.

Yes, but unless your fermenter has just been forged or, more realistically, just underwent pickling the oxide layer will already be there having formed in the weeks or months since the part left the factory. Since citric acid passivation does not remove it but only improves its characteristics there is no need whatsoever to wait for it to form in the first place.

 

[CodeSection]

Well, I guess I have been waiting too long as it has been five days on my BK and MT, and four days with my bright tank. I guess I will transfer the beer from the fermenter to the bright tank tomorrow. Then passivate the fermenter after cleaning so as I can brew this weekend.

Thanks for the responses!

 

[RPh_Guy]

Since citric acid passivation does not remove it but only improves its characteristics there is no need whatsoever to wait for it to form in the first place.

The citric acid "improves its characteristics" by stripping a particular metal from the surface. It's know to remove both iron and iron oxide, so it does penetrate the oxide layer, at least in some sense.

Logically, the newly exposed chromium (where iron was removed) needs to oxidize. This is presumed to occur via air exposure. The question is how long does this take.

 

[Vale71]

This all happens at the atomic level so there is really no "penetration" in the mechanical sense and there is no exposed chromium that needs to oxidize. What happens is that the surface layer that is made of a chromium-oxide and iron/iron-oxide alloy becomes a pure chromium-oxide layer which is much more resistant to corrosion.
If there are macroscopic iron contaminations, such as residue from welding and/or mechanical polishing, then a simple citric acid treatment won't be effective. That's when you'd need a complete pickling followed by passivation or, better yet, some form of electropolishing which combines pickling and passivation is a single step.

 

[RPh_Guy]

This all happens at the atomic level

This just means you can't see it happening. When iron is removed, how could it not expose additional chromium? That's the whole point of the treatment -- increasing the amount of surface chromium which then needs to oxidize.