Old used equipment...passivation procedures

[Tash]

I'm very close to assembling a 10hl brewhouse. I know the stainless is going to need to be passivated. Though I understand the need to get the oxide layer back to the tank walls...I am not certain about a few things.

1. Can the Nitric/Phosphoric blends we see from various suppliers adequate?
What percentage of Nitric needs to be in this blend. What temperature is ideal? What is the appropriate length of circulation? Rinse?

2. Should I be concerned about running this solution through the heat exchanger? Is it going to harm the gaskets?

3. How can I tell that I have succeeded in repassivating?

Thanks!

Tash

[aswissbrewer]

Hi
I have had good experience with commercial nitric acid formulations. The reps will be able to recommend something. (I used "Pascal" from JohnsonDiversey)
The tanks etc. have to be cleaned and rinsed in advance of course. Mostly concentrations (of the formulation) of 1-3% are recommended. Contact time should be around an hour and the temp shouldn't go over 60 C (140F).

Under these conditions I never noticed any problems with seals and gaskets.

Some people recommend letting the tank dry off before rinsing it after the acid cycle. Others claim this isn't necessary. What seems to be important is ensuring that enough air resp. oxygen, gets to the surfaces - vent out all CO2 adequately.
Good luck

[gitchegumee]

The usual procedure is a manual cleaning to remove any construction debris, tape, films, etc followed by a thorough caustic (NaOH) cleaning. After a hot rinse, the passivation is achieved with a nitric acid wash of about 15% HNO3 at a temperature of about 110 F for a period of about 10 minutes. You MUST air dry the tank to assure the formation of a passivated, oxidized layer! This is not an option! Be careful with chemicals!

[gitchegumee]

Please see corrections to passivation technique I described above here:
http://www.probrewer.com/vbulletin/s...2611#post72611