Stopping rust/ passivating stainless steel

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wilfh
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Stopping rust/ passivating stainless steel

Post by wilfh » Mon Nov 09, 2020 9:53 pm

I have recently got a four inch triclamp port welded to the top of a 50l beer keg. I understood that to stop rusting I should passivate the welds with a strong 1:1 paste of bar keepers friend for 30 minutes before washing and drying.

Unfortunately this hasn’t done the trick and Ive already got rust spots around the weld.

Does anyone have any suggestions about how I stop this?
Thanks
Wilf

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Hanglow
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Re: Stopping rust/ passivating stainless steel

Post by Hanglow » Tue Nov 10, 2020 11:13 am

Use citric acid instead as barkeepers friend is just a cleaner, it won't properly passivate SS

method and reasoning:

https://modernbrewhouse.com/wiki/Passivation

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PeeBee
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Re: Stopping rust/ passivating stainless steel

Post by PeeBee » Tue Nov 10, 2020 1:33 pm

Trouble is, it isn't stainless steel you are trying to "passivate". Welding stainless steel is tricky, and the weld might well contain inclusions of plain carbon steel. Passivation of stainless steel relies on the surface formation of chromium oxide. If there are areas of no chromium, there can be no chromium oxide and so you get iron oxide (rust) instead.

Apparently the worst thing you can do is remove the rust with wire-wool. The action forces more plain steel (from the wire-wool) into the surface which … rusts!

I believe there are specific preparation to improve the situation (I have no specific example) otherwise its polish off the rust from surfaces in contact with beer each time you use it (it wont rust while beer is in the fermenter because there wont be any oxygen).


This is a timely post. I'm about to get a four-inch tri-clamp port installed into my fermenter. Perhaps I should pay more attention to how it is done? The link from "Hanglow" is interesting, in particular it explains that acid treatment (phosphoric acid - starsan - and oxalic acid - barkeepers friend - are not effective whereas citric acid is, it claims) do not "passivate" but prepares the surface for more effective "passivation" which just requires oxygen.
Cask-conditioned style ale out of a keg/Cornie (the "treatise"): https://drive.google.com/file/d/0BwzEv5 ... rDKRMjcO1g
Water report demystified (the "Defuddler"; removes the nonsense!): https://drive.google.com/drive/folders/ ... sp=sharing

wilfh
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Re: Stopping rust/ passivating stainless steel

Post by wilfh » Tue Nov 10, 2020 2:55 pm

Thanks very much. Will have a go and report back. Have you tried it?
Wilf

Carnot
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Re: Stopping rust/ passivating stainless steel

Post by Carnot » Tue Nov 24, 2020 6:40 pm

Oh dear,

I wish I had spotted this earlier. Oxalic acid or Brewers Friend is not the right way. Likewise you must be very careful with abrasives. Never use wire wool or steel abraisives( wire brush- even stainless)

Please look here for passivating stainlees steel. This is a repost on citric acid passivation from the BSSA

https://bssa.org.uk/bssa_articles/passi ... ss-steels/

http://www.elmerwallace.co.uk/Passivati ... el/B13.htm

Both tell the same tale. Foloo this methology and you should be fine.

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