Passivating stainless with citric acid

[Bensiff]

I want to passivate my new kettles with citric acid but can't find the information to do so. Anyone know a procedure for this?

 

[stevehaun]

A quick google search yielded the following:
10% solution of citric acid @150 F for 30 minutes.

I think this is very similar to what I did when I built my home brewery.

 

[heckels]

Why not use some Barkeepers Friend? It'll passivate for you.

 

[CRoth36]

Citric does the trick. All sorts of info out there about it. When I did it I made a 5% solution and heated it up to around 160ish and did tht for like an hour. Could have been more time that was needed but doesn't hurt. Pretty sure the idea is the stronger solution the less time. From my understanding you could do a very weak solution it would just take longer to do. Let us know what you did.

 

[Bensiff]

Son of a...I looked at a dozen pages and could not find how strong a solution was needed, just the temp. Well that is why I asked here. I have citric acid crystals on hand, any thoughts on using that to make the solution, such as can I use pH to determine what strength the solution is?

 

[Bensiff]

Why not use some Barkeepers Friend? It'll passivate for you.

The only thing I could really find on this is from John Palmer, seems like it is not a standard procedure for passivating like citric is. However hand scrubbing everything and then rinsing down with some BKF seems like it may be much faster, albeit messier.

 

[heckels]

The only thing I could really find on this is from John Palmer, seems like it is not a standard procedure for passivating like citric is. However hand scrubbing everything and then rinsing down with some BKF seems like it may be much faster, albeit messier.

When my Stout Kettles came that was their recommendation for passivating the new stainless. I don't recall what the key component was in there that they said would cause the reaction but I figured I'd trust em.

 

[stevehaun]

Nothing wrong with Bar Keepers Friend - Oxalic acid.
Back to Citric Acid:
5-10% solution will work. Heat and time are the other important variables.
I don't know if you are asking how to make a solution with your citric crystals??
10% solution = 10 grams/100 ml or 0.836 pounds/gallon
5% solution = 5 grams/100 ml or 0.418 pounds/gallon

 

[dmfa200]

Passivating stainless is overrated.
I could show you my keggles that are unpassivated, welded on, scrubbed with stainless scrubbies, ground with abrasives with no sign of corrosion after more than 2 years of brewing in them.
Don't believe the hype.
Passivation is for the removal of free iron on the surface of stainless so that when stainless steel forms it's protective oxide layer there will be no iron that gets trapped underneath.

bensiff, do you have reason to believe that the surface of your equipment has been contaminated with free iron particles?

I know I'm gonna catch some crap for what I'm saying, but if it makes you sleep better at night, knock yourself out and passivate to your hearts content.

 

[Bensiff]

Passivating stainless is overrated. I could show you my keggles that are unpassivated, welded on, scrubbed with stainless scrubbies, ground with abrasives with no sign of corrosion after more than 2 years of brewing in them. Don't believe the hype. Passivation is for the removal of free iron on the surface of stainless so that when stainless steel forms it's protective oxide layer there will be no iron that gets trapped underneath. bensiff, do you have reason to believe that the surface of your equipment has been contaminated with free iron particles? I know I'm gonna catch some crap for what I'm saying, but if it makes you sleep better at night, knock yourself out and passivate to your hearts content.

There are a few spots of minor surface rust on the inside of ports. Probably due to the heat from the welds combined with that area not getting polished afterwords. If your keggles are rust free you are benefitting from the oxide layer doing its thing, even if you didn't take the steps to aid in the development of it.

 

[kladue]

Here is the procedure from a 3+ year old post on passivisation:
"You can repassivate with citric and ascorbic acid in hot water like we do for SS repassivation after welding or grinding and breaking the surface passivation. A 50-50 mix of 1 Lb acid blend in 4gallons of water, heated to 180 degrees, and left to cool for about 6-8 hours will extract the soluble iron and rebuild the oxides to protect the stainless steel where it has been heat affected. This is slower than the nitric acid method but safely do able by the homebrewer, and is the method of choice in the food and beverage handling industry these days. You will only need to cover the weld area, not fill entire keg as only weld or grinding/ polishing area needs attention."

 

[dmfa200]

There are a few spots of minor surface rust on the inside of ports. Probably due to the heat from the welds combined with that area not getting polished afterwords. If your keggles are rust free you are benefitting from the oxide layer doing its thing, even if you didn't take the steps to aid in the development of it.

I am benefiting from my knowledge and experience I have in working with stainless steel.
I never use any consumables that have been in contact with other metals other than stainless steel.

When companies manufacture products made of stainless steel it is hard to insure with 100% certainty that stainless materials have not been exposed to contaminates. Passivation is a measure to insure that stainless is free of contaminates so that it's protective oxide layer can form undisturbed.
Being that I am the only one that has worked on my equipment I can feel confident that I took the necessary precautions to prevent contamination.

It's one thing to be cautious when producing equipment worth tens of thousands of dollars. You don't want to take any chances.
But a kegle or a pot? I'm sorry, I think people worry too much.
I mean how much stainless steel cookware do people have in their homes?
Do you think anybody worries about passivating their cookware?

I'm not saying everyone is foolish for wanting to do it. I just think people worry too much about it.

Stainless steel is not a ceramic doll. It's pretty effin tough! That's why it's so popular.

 

[mattd2]

I am benefiting from my knowledge and experience I have in working with stainless steel.
I never use any consumables that have been in contact with other metals other than stainless steel.

When companies manufacture products made of stainless steel it is hard to insure with 100% certainty that stainless materials have not been exposed to contaminates. Passivation is a measure to insure that stainless is free of contaminates so that it's protective oxide layer can form undisturbed.
Being that I am the only one that has worked on my equipment I can feel confident that I took the necessary precautions to prevent contamination.

It's one thing to be cautious when producing equipment worth tens of thousands of dollars. You don't want to take any chances.
But a kegle or a pot? I'm sorry, I think people worry too much.
I mean how much stainless steel cookware do people have in their homes?
Do you think anybody worries about passivating their cookware?

I'm not saying everyone is foolish for wanting to do it. I just think people worry too much about it.

Stainless steel is not a ceramic doll. It's pretty effin tough! That's why it's so popular.

And anyway doesn't SS saelf passivate over time, taking steps to passivate it just speeds it up. And anyway if we are really worrying shouldn't we be pickling any heat affected SS before passivating anyway - not something I think the weekend DIY should try without fully understanding the hazards.

 

[Bensiff]

I am benefiting from my knowledge and experience I have in working with stainless steel.
I never use any consumables that have been in contact with other metals other than stainless steel.

When companies manufacture products made of stainless steel it is hard to insure with 100% certainty that stainless materials have not been exposed to contaminates. Passivation is a measure to insure that stainless is free of contaminates so that it's protective oxide layer can form undisturbed.
Being that I am the only one that has worked on my equipment I can feel confident that I took the necessary precautions to prevent contamination.

It's one thing to be cautious when producing equipment worth tens of thousands of dollars. You don't want to take any chances.
But a kegle or a pot? I'm sorry, I think people worry too much.
I mean how much stainless steel cookware do people have in their homes?
Do you think anybody worries about passivating their cookware?

I'm not saying everyone is foolish for wanting to do it. I just think people worry too much about it.

Stainless steel is not a ceramic doll. It's pretty effin tough! That's why it's so popular.

I understand what you are saying, I haven't bothered with my other pots and equipment and never had an issue. However, when I have nearly $2k tied into custom pots and there are a few areas that have surface rust, I know they need a little more than a scrubby and PBW. So, my point isn't to debate the merits of passivation...just need to know how to do it.

 

[txjoe]

Some research done by Boeing shows a 15% by weight solution of citric acid used at ambient temperature with a two hour soak is as effective as nitric acid or better.

http://www.astropak.com/downloads/technical_papers/boeing_passivation.pdf

 

[orangehero]

If your homebrew store carries it, you can also use Five Star Acid #5 (phosphoric and nitric acid mix).

 

[seeGarzz]

These guys have some good information on using citric acid for passivating. We did an alkaline wash and then one of their citrisurf products for a new tank at a small brewery where I help out. You can passivate at lower temps but have to run the process a little longer.

 

[limulus]

Hey guys, I have never passivated any of my stainless. I just got one of the stainless conical brewbuckets from ssbrewtech. I have not used it yet and think I'll try this. I don't have citric acid but I do have a new can of Barkeeper's Friend. I'm going to do some more reading and find a method using Barkeeper's Friend.

 

[PaulyWallnuts]

And anyway doesn't SS saelf passivate over time, taking steps to passivate it just speeds it up. And anyway if we are really worrying shouldn't we be pickling any heat affected SS before passivating anyway - not something I think the weekend DIY should try without fully understanding the hazards.

I realize this post is old, but I stumbled upon it and wanted to set the record straight for anyone who stumbles upon it like I did.

Yes, stainless steel self passivates to a degree but if there is iron on the surface it must be removed so that that area of the surface can form a chrome-oxide layer. Removing that free iron is "passivation".

No, it is not necessary to pickle the heat affected zone. If you passivate the heat affected zone, it will still have weld tint on it but it will have the corrosion resistance that is imparted by the passivation. You are right that the weekend DIY person should not mess around with pickling chemistry.

There is a good line of citric acid based products for passivation of stainless steel brewing equipment called CitriSurf. Here's the link: http://citrisurf.com/brewery-passivation/