Cleaning and passivating stainless steel

[Simonh82]

I'm about to pull the trigger on a 55L SS Brewtech stainless steel kettle. There's lots of info on their website about cleaning and passivating the kettle before using it for the first time. Whenever I've got new bits of stainless before I've just given them a good clean with soapy water and maybe some PBW, but the info on SS Brewtech's site specifically says PBW isn't enough. It says to use Tri Sodium Phosphate for cleaning, which is very nasty stuff from what I understand, and then nitric acid or citric acid to passivate. I can get citric acid easily enough but the quantities are pretty crazy. They suggest 10% by weight so to fill a 55L pot I will need 5.5KG of citric acid.

This all seems pretty crazy when I've previously never had an issue with any of my other stainless items. Would it be awful if I just gave it a really good clean and dry and maybe a squirt with some starsan?

 

[LeeH]

I agree, I have 3 75L brewtech pots and a half barrel conical. I did passivate the pots after a while but only because some crappy brew builder probes went rusty.

The conical never got done and surprise surprise no rust.

If you do get a spot of rust just use bar keepers friend to clean it off and leave to dry.

Just remove any manufacturing grease with a cleaner of your choice e.g an all purpose cleaner, and leave to dry. Some sources say star san is the incorrect type of acid but for piece of mind I always finish by fully wetting inside and out with a trigger spray and leaving to to dry after every use. It stays shiny that way as my water is very hard.

No issues here.

 

[Honk]

Someone suggested a concentrated solution of starsan sprayed on on another thread which I thought was a good idea.

I soaked my brewbucket in starsan but not concentrated to proper levels for passivating when I first got it, no problems

 

[terrym]

Has the forum got a real qualified metallurgist who can provide an informed opinion on passivation of 'stainless steel'?
Corrosion is a complex subject and I suspect some of the stuff about passivation on our forum is wrong.
My understanding is that the 'passivation' layer of chromium oxide on the surface of good quality stainless steel will remain intact unless it is removed mechanically and/or chemically. And if it is removed it can be simply reinstated by exposing to air or water. Nitric acid is often used commercially since it is a strong oxidising agent.
So assuming brewing kit is fabricated from the correct type of SS for the service conditions, it shouldn't chemically corrode in use and release metal ions unless the surface is mechanically damaged say by cleaning. That said if really cheap SS that has been used and there are iron inclusions they will continue to corrode until they disappear.
So hopefully we have a metallurgist who can set me and everyone else straight rather than relying on the word of enthusiastic amateurs or a journo with a GCSE in chemistry.

 

[foxbat]

TSP for first-time washing (removes left over grease from manufacturing). It's not nasty stuff at all, in fact it's an EU-approved food additive. It's banned for use in many places because if it ends up in rivers then the phosphates can cause algae blooms.

Once washed, polish with Bar Keeper's Friend to passivate then rinse off. If your pot has laser etched markings, avoid going over those with BKF - it can remove them.

I do this simple procedure with every SS vessel that I buy.

 

[peebee]

TSP for first-time washing (removes left over grease from manufacturing). It's not nasty stuff at all, in fact it's an EU-approved food additive. It's banned for use in many places because if it ends up in rivers then the phosphates can cause algae blooms. ...

In strong concentration it can be nasty stuff! It's quite strongly caustic and eye-protection should be considered essential. Some people don't bother with rubber gloves, but it doesn't take much to put some on. Dust masks when mixing the powder is no bad idea either. But it is a league away from Caustic Soda which is awful stuff (and some say to use it hot - count me out).

"TSP" is somewhere between detergent and caustic soda, don't get it on bare wood or painted surfaces (it is used as a paint stripper). But it is a very effective grease cleaner, and to put it in context we are all happy using "Star San" and that stuff (neat) will strip epoxy based varnish no bother (as I know only too well).

I've got some "Bar-keeper's Friend" to try and remove the dark stains left on a stainless steel fermenter by VWP. But as its now just a cosmetic stain I probably wont bother. There are loads of ways to damage stainless steel - the best policy for cleaning is probably warm water and a non-abrasive cloth.

I discussed TSP earlier this month (https://www.thehomebrewforum.co.uk/threads/trisodium-phosphate-cleaning-concentration.80007/) to try and get the best concentration to use - I concluded 10-20g per litre to be right (I used 15g/l - you just need to swab or spray it on, carefully, and wash off a few minutes later; no need to soak). I used it to get machine oil off "Grainfather" stuff; the oil is probably left on because Chinese stainless steel ("Grainfathers" are made in China) is notorious for going rusty! I think a lot of American "stainless steel" is Chinese too. My guess is the amount of chromium in Chinese SS isn't as much as might be desirable, hence the instructions to also accelerate the natural process of "passivating" the steel (see @terrym 's post above).

 

[Simonh82]

Which version of bar keepers friend do I want, there seems to be a cleaner and polish, power spray, power cream and a stain remover cream?

 

[foxbat]

Which version of bar keepers friend do I want, there seems to be a cleaner and polish, power spray, power cream and a stain remover cream?

This is the one I use:

(contains Oxalic acid, Citric acid, Sodium carbonate)

 

[Simonh82]

Has the forum got a real qualified metallurgist who can provide an informed opinion on passivation of 'stainless steel'?
Corrosion is a complex subject and I suspect some of the stuff about passivation on our forum is wrong.
My understanding is that the 'passivation' layer of chromium oxide on the surface of good quality stainless steel will remain intact unless it is removed mechanically and/or chemically. And if it is removed it can be simply reinstated by exposing to air or water. Nitric acid is often used commercially since it is a strong oxidising agent.
So assuming brewing kit is fabricated from the correct type of SS for the service conditions, it shouldn't chemically corrode in use and release metal ions unless the surface is mechanically damaged say by cleaning. That said if really cheap SS that has been used and there are iron inclusions they will continue to corrode until they disappear.
So hopefully we have a metallurgist who can set me and everyone else straight rather than relying on the word of enthusiastic amateurs or a journo with a GCSE in chemistry.

I'm not sure if that would even help. I was reading some stuff on a forum for metallurgist called something like finishing.com and there was clearly still a lot of debate about the best way to passivate SS and whether citric acid was a viable option.