Hi Ray
Thanks for your note, Ill check out your site.
I think we will be definitely looking to go with a citric acid based protocol, since it seems like the guys already have some of the material.
Im thinking something along the lines of the boeing tech paper might work:
http://www.astropak.com/downloads/technical_papers/boeing_passivation.pdf
Passivation of Aerospace
Stainless Steel Parts with Citric Acid Solutions
Stephen P. Gaydos, The Boeing Company, St. Louis, Missouri, USA
Optimization of Citric Acid Passivation Solution –
ASTM A 967 allows solutions containing 4 to 10 weight % citric acid at solution temperatures ranging from 70 to 160 oF. The combination of citric acid solutions available to test was too large to handle so a 3 factor - 2 level Design of Experiment5 (DoE) was conducted to determine the optimum citric acid concentration, solution temperature and immersion time. The citric acid was controlled at 3 and 15 weight %, solution temperature was controlled at 75 and 150 oF, and immersion time was controlled at 5 and 30 minutes. The DoE results showed that concentration was not significant, but temperature was important. 150 oF at short or long immersion times produced good passivation results, but long immersion time at room temperature was also good. In order to conserve energy, it was determined that the optimum citric acid passivation solution was 15 weight %, at ambient temperature, and an immersion time of 2 hours. The higher citric acid concentration level was selected because the passivation tank used for this evaluation was small in relation to the amount of test specimens that were passivated, and it was thought that the higher citric acid concentration would provide a more consistent passivation treatment for all of the test specimens processed.
I suppose since the brew vessels are of a considerable size, it wont be practical to fill the vessel entirely with passivating solution. Im thinking we ought to run a recirulating pump type set up for the duration of the treatment.
Do you know if the external surfaces of these types of brew vessels are typically treated too?
-C
