Concentrations of citric and phosphoric acid

[ben@atlas]

I would like some advice on the types and concentrations of acids for CIP cycles and for passivation. I currently have phosphoric and citric acid at my disposal. How strong should I make my solutions for these two processes? I'd really appreciate any recommendations.

[dick murton]

I assume you are passivating stainless in a new installation. You really need to use an oxidising agent, the most effective in CIP style installations being nitric acid. H3PO4 is not oxidising and will not passivate. A few percent, ideally warm, and recirculate for 30 minutes or so. A bit crude I know, but this seems to work fairly well providing hte plant has been thoroughly degreased beforehand and the welds have been ground back OK. Stainless sheet as used for vessels and pipes should be OK as is, it is the welds that normally require the passivation.

I have no experience of citric acid. It doesn't sound like an oxidising agent, and if it isn't, will not passivate, so you will be wasting your time using this.

[yap]

a lot of suppliers these days seem to be recommending to passivate with citric due to safety concerns regarding nitric. does it work as well? not sure... i was recommended 10% by weight, 30 minutes at 150F or 40 minutes at 135F.

be sure to clean the tank well to remove machining grease etc before you do it..

[CraftBeerIndia]

Nitric

I agree. I used hot Nitric @ 70ºC about 2%v/v (2 litres in 100L water) to passivate new 10HL and 20HL unitanks. From the supplier, the package said Nitric Acid 88%. Be really careful with this stuff! We used a 20min recirc for each tank. I think we first did a caustic and a rinse cycle...and then brought out the nitric. That's probably overkill, but that's what we did and it worked fine.

[ben@atlas]

Thanks for the advice!

[gitchegumee]

A dozen threads on this topic already.

http://www.probrewer.com/vbulletin/showthread.php?t=24106