tom_hampton said:
I am not a chemist. However, my understanding is that the silicate can be easily removed with a weak acid solution such as vinegar or....Star-San. I have left PBW sitting in my stainless for a week without any visible silicate deposits. Quite the opposite, actually. It was nice and squeaky and clean.
It is also my understanding that the loss of passivation, and resultant exposure to corrosion is a chlorite (eg. sodium hypochlorite, aka bleach) problem. Rather than a metasilicate problem. Palmer recommends percarbonate/metasilicate based cleansers, as the clensers-of-choice for stainless.
At pH of 10 and up, chlorine does not react with stainless. However, time, temperature and chelation can change the buffering strength of the solution. Most commercial breweries do or have used chlorinated caustic for cleaning tanks and kettles. In addition, chlorine dioxide is a sanitizer used in many breweries and food production plants. As long as the steel is properly passivated, no issues arise.
In your case, Tom, I don't think that you have any steel long enough to lose passivation.
Repeated dry heating of stainless and other sorts of "abuse" over time can remove chromium from stainless. As I understand it, Sodium Metasilicate can form a coating on unpassivated parts of the steel, through a redox reaction with the unprotected steel as it cools and dries. The resulting matrix with the silica is not easy to dissolve in acids. Dirk Loeffler (who is a chemist) repeatedly warns that long term use of metasilicates can lead to an unremovable residue that has to be sanded off.
In my brewery, I use both PBW and a Caustic for cleaning. PBW has the advantage of working in a CO2 environment, where caustic soda will cause a rapid pressure collapse as it reacts with the CO2 to form a harmless salt. Since my tanks have to be filtered, cleaned and refilled in a matter of 1 to 2 shifts, PBW lets me skip the air purge and (with bright tanks) refilling with CO2.
All things considered, ...
It also works much quicker hot.
Ouch. ...I try to follow the "proper procedures are assumed" when talking to another experienced brewer.
The truth is that I participate in this forum for fun. It's a forum that talks about actually making beer, through the lens of specific brewing software. A lot less noise than other forums.
I'm not looking to razzle dazzle every nuance or detail, just inform. I wasn't gifted with a great memory. I have to work hard for every scrap of information I know. I compensate by having a very good reference library (of real books!).