Passivate equipment...

[Hayden123982]

the link up a bit said otherwise.

It said you can't get citric acid on amazon?

 

[Qhrumphf]

The use of citric acid as a direct passivation agent is pretty recent research but there's evidence for it.

 

[Qhrumphf]

Also my LHBS stocks citric acid. Winemakers use it. I use it to make invert sugar. It's easier to come by than nitric acid for sure.

For passivation quantities probably Amazon is the best bet.

 

[Bilsch]

Actually, yeah it does



Yeah there clearly is. The blend of phosphoric acid and dodecylbenzenesulfonic acid in StarSan will passivate stainless steel

I'd like to see the data to back that up.

 

[SpikeBrewing]

Thought we'd chime in as there is a lot of back and forth going on...

We've seen a lot of questions and comments about passivating stainless. Our engineers helped us put together a FAQ regarding this topic. We highly doubt this will settle any arguments however our stance is based on our testing and experience, industry professionals we work with along with industry studies like the link below.

From our FAQ page regarding passivating equipment on first use:
"Passivization has become a buzz word as of recently and there's a lot of misinformation regarding it. Stainless steel naturally passivates with oxygen. There is no need to passivate your equipment at home. There are no professional standards that recommend Star-San (Phosphoric Acid) at room temperature to passivate stainless steel. If you do see a small surface rust spot hit it with Bar Keepers Friend and it'll be gone forever. We do recommend a good scrub with dish soap before use to remove any oils from manufacturing and to provide a clean surface for contact with something that will be ingested.

Please see attached for a study done by Outokumpu Stainless showing that stainless passivated in air was almost as effective as passivating with harsh chemicals."

Link to study

 

[Qhrumphf]

I'd like to see the data to back that up.

Some papers behind a paywall (that I can't see) might back it up. I reserve judgement.

I guess the ultimate point is "it's your gear".

Stainless WILL self passivate in oxygen when fully clean. It takes time. Potentially microscopic, even molecular level contamination can inhibit than passivation and become a seed for corrosion. These are scientific knowns.

If you're confident in your equipment supplier providing gear that, with a rudimentary cleaning to remove fabrication oil, will quickly and adequately self-passivate, then go for it. If you find rust specks and deal with them quickly to repassivate targeted areas, you will probably be ok. If you have pervasive rust hopefully whatever equipment supplier stands by their goods and just replaces it for you.

You're homebrewing. Not spending 5 or 6 figures on gear (with long runs of pipe you can't visually inspect) should corrosion compromise a vessel. And not dealing with 5 or 6 figures of lost revenue if corrosion compromises a batch.

 

[SoCal-Doug]

That's a pretty bold statement to say there is no reason to passivate. Are you absolutely sure about that ?

Yup! And what I actually said was "unless you see signs that it NEEDS repassivating, there is no reason to passivate it". Furthermore, anything that could be done at home, without serious equipment and health/injury risks, is temporary and a bit hokey, at best.

"Passivization has become a buzz word as of recently and there's a lot of misinformation regarding it. Stainless steel naturally passivates with oxygen. There is no need to passivate your equipment at home. There are no professional standards that recommend Star-San (Phosphoric Acid) at room temperature to passivate stainless steel. If you do see a small surface rust spot hit it with Bar Keepers Friend and it'll be gone forever. We do recommend a good scrub with dish soap before use to remove any oils from manufacturing and to provide a clean surface for contact with something that will be ingested.

 

[Bilsch]

There is another reason besides corrosion that brewers might want to passivate or more specifically remove free iron from the surface of the stainless. That is to reduce the possibility of Fe catalyzed oxidation reactions in the beer. This was apparently the reason Coors originally came up with using citric acid.

 

[Rev2010]

There is another reason besides corrosion that brewers might want to passivate or more specifically remove free iron from the surface of the stainless. That is to reduce the possibility of Fe catalyzed oxidation reactions in the beer. This was apparently the reason Coors originally came up with using citric acid.

Maybe Coors tasted better before making this change


Rev.

 

[NewJersey]

It said you can't get citric acid on amazon?

no, lol

The use of citric acid as a direct passivation agent is pretty recent research but there's evidence for it.

this

 

[CodeSection]

..... Citric acid is the least expensive method and it won't remove etchings (tried it on my SSB Brew Kettles).

I'm getting ready to assemble and clean my new SS Brewtech Brite Tank. When using citric acid for passivation, what dosage did you use and how long did you have it soak?

 

[day_trippr]

Good article on the process here: https://www.pfonline.com/articles/citric-acid-passivation-of-stainless-steel
Summary: CA concentration of 4-10%, can be left for "longer than necessary" (compared to nitric acid process, I presume)...

Cheers!

 

[CodeSection]

Good article on the process here: https://www.pfonline.com/articles/citric-acid-passivation-of-stainless-steel
Summary: CA concentration of 4-10%, can be left for "longer than necessary" (compared to nitric acid process, I presume)...

Cheers!

Thanks for the link. Hopefully, I'm understanding the 4-10% citric acid by weight mentioned in the article.

So, one gallon of water weighs approximately 8.34 pounds. A 20 gallon bright tank then would weigh 166.80 pounds. Critic acid at 4% of weight would be 166.8 x .04 = 6.672 pounds.`

So, one should use anywhere from 6.672-16.68 pounds of citric acid for passivation of a 20 gallon tank? Am I understanding this correctly?

 

[CodeSection]

Citric acid at 4% (4g per 100mL) at the right temperature for the right duration (60 minutes at 140°F or higher) will selectively remove iron from the surface, reducing the chance rust will form in the future. It's called passivation....

Reading this post in another thread confirms my previous calculations....

 

[RPh_Guy]

What is passivation?
Passivation is using an acid to selectively remove iron atoms from the surface of stainless steel. Oxygen can then react with the chromium to form an oxide layer.

Which acids can passivate?
Nitric acid and citric acid passivate stainless steel. Citric acid is much less hazardous.

NO OTHER ACIDS ARE KNOWN TO WORK -- this includes BKF (oxalic acid) and Star San (phosphoric acid). Stop spreading myths that these acids passivate.

AIR DOES NOT PASSIVATE -- air does not remove iron atoms from the surface of stainless steel, not even under high wind conditions.

PHYSICAL PROCESSES DO NOT PASSIVATE -- scrubbing, grinding, polishing, etc. does not selectively remove iron from the surface.

Nitric acid directly contributes to the oxide layer whereas citric acid does not. After using citric acid to passivate, the oxide layer forms over several days of air exposure.

Do I need to passivate my stainless?
Most likely passivation is unneeded if you're just worried about possible corrosion. 304 stainless steel and even lower grades of stainless are pretty resistant to corrosion in the environment of wort/beer production and the cleaning chemicals used by homebrewers.

However:
Some of us (low oxygen brewers) want to prevent iron from interacting with our beer & wort because it catalyzes staling reactions, so passivation is a practical way to prevent this.

Cheers.

 

[CodeSection]

....After using citric acid to passivate, the oxide layer forms over several days of air exposure.

Do I need to passivate my stainless?
Most likely passivation is unneeded if you're just worried about possible corrosion. 304 stainless steel and even lower grades of stainless are pretty resistant to corrosion in the environment of wort/beer production and the cleaning chemicals used by homebrewers....

Good info here. Since I have to order CA and now learning it will take several days of air exposure, I'm going to wait until after my next brew. The week delay will impact my current and future batch.

I have a current batch that I want to transfer from my CF10 to the bright tank so as I can brew another batch so that it is ready by St. Patrick's Day. I initially read about SS Brewtech's instructions to use 1 oz per gallon to passivate. I should have researched this topic earlier. Lesson learned.

After reading here on HBT, I now have a better understanding. So, after I empty the bright tank and bottle, I will clean and then passivate it with CA.

 

[Bilsch]

Thanks for the link. Hopefully, I'm understanding the 4-10% citric acid by weight mentioned in the article.

Yes 4% of the weight of the water in citric. And you only need to use the 4% solution at 170/180f for an hour. Don’t forget to put all your other stainless parts and fittings that will fit in there and passivate it all at the same time.

Ps it’s much easier to do these solution calculations in metric units.

 

[CodeSection]

....Don’t forget to put all your other stainless parts and fittings that will fit in there and passivate it all at the same time....

Would that include valves? Would the citric acid have any negative affect on the rubber component inside the valve?

 

[Bilsch]

Citric is safe with plastic and rubber so you are good there but it’s always best to disassemble valves so the citric can get contact to all SS nooks and crannies.

One more thing.. After about a half hour soaking you will see your solution go a nice bright yellow/green color. This is the free iron you removed from the surface that is now ferric citrate and an indication of a job well done.

 

[CodeSection]

Citric is safe with plastic and rubber so you are good there but it’s always best to disassemble valves so the citric can get contact to all SS nooks and crannies.

One more thing.. After about a half hour soaking you will see your solution go a nice bright yellow/green color. This is the free iron you removed from the surface that is now ferric citrate and an indication of a job well done.

So, once you soak everything at the desired CA amount, temp and time, do you just drain the solution and allow everything to dry? Or do you rinse everything with clean water and then allow to dry?

 

[day_trippr]

Rinse everything to be sure to get all the iron compounds out, wipe dry then air dry...

Cheers!

 

[day_trippr]

I should have noted "using RO or distilled water" for the first rinse cycle, as per a few of the processes I read, to avoid actually contaminating the acidified metal surface with water borne minerals that might inadvertently create localized deposits...

Cheers!

 

[CodeSection]

I should have noted "using RO or distilled water" for the first rinse cycle, as per a few of the processes I read, to avoid actually contaminating the acidified metal surface with water borne minerals that might inadvertently create localized deposits...

Cheers!

Too late....

 

[day_trippr]

Sorry, I've been "learning while doing", and only saw this recommendation this morning, just before I fried up my modified SS IC in 6% CA for an hour this afternoon. When I read the same thing at the third site I actually scooted right down to my RO controller and set it to run 6 gallons so it'd be ready to dunk when the frying was done.

Anyway, I have to believe the issue is actually minor given our usage - these were commercial processing companies that do extreme stuff, and we're not cranking out pharmaceutics after all

Cheers!

 

[Vale71]

Citric acid will not remove the existing passivation layer but will only remove the iron and iron oxide residual contamination which makes the layer less effective. The layer will also increase somewhat in thickness. This means you don't need air exposure to passivate as the passivation is actually done by the acid.

At the commercial level passivation is always preceded by "pickling" which actually removes the surface layer. The subsequent passivation step will build up the layer from scratch. This is a lot more effective but requires the use of dangerous chemicals and would be overkill for our equipment anyway.

 

[RPh_Guy]

Citric acid will not remove the existing passivation layer but will only remove the iron and iron oxide residual contamination which makes the layer less effective. The layer will also increase somewhat in thickness. This means you don't need air exposure to passivate as the passivation is actually done by the acid.

Got a source for this info? Citric acid isn't known as an "oxidizing acid", unlike nitric acid.

 

[Vale71]

Here you go:

https://www.besttechnologyinc.com/passivation-systems/citrisurf-citric-acid-passivation-solution/

Some useful information on contact times and temperatures as well.

 

[RPh_Guy]

Here you go:

https://www.besttechnologyinc.com/passivation-systems/citrisurf-citric-acid-passivation-solution/

Some useful information on contact times and temperatures as well.

If you click on the "what is passivation?" link from that page, it says the opposite of what you said. The acid removes free iron and air adds the oxide layer.

This means you don't need air exposure to passivate as the passivation is actually done by the acid.

So this is incorrect.

Citric acid will not remove the existing passivation layer but will only remove the iron and iron oxide residual contamination which makes the layer less effective. The layer will also increase somewhat in thickness.

And I'm still wondering where you got this info.

What do you mean by "less effective"? Citric acid passivation has always been shown to be equal or superior to nitric acid passivation.

There's also debate about whether even nitric acid actual directly adds the oxide layer because it is known that extended contact times can cause pitting/corrosion, which is arguably mutually exclusive of directly creating a surface oxide layer.

 

[Vale71]

If you click on the "what is passivation?" link from that page, it says the opposite of what you said. The acid removes free iron and air adds the oxide layer.

So this is incorrect.

And I'm still wondering where you got this info.

What do you mean by "less effective"? Citric acid passivation has always been shown to be equal or superior to nitric acid passivation.

There's also debate about whether even nitric acid actual directly adds the oxide layer because it is known that extended contact times can cause pitting/corrosion, which is arguably mutually exclusive of directly creating a surface oxide layer.

"Another benefit of citric acid passivation using CitriSurf® is that the treatment removes only the iron from the surface, and not other metals in the alloy. This affects the depth of the surface treatment and mitigates against changes in the overall size of the part, which can be an important factor in close tolerance and high-precision machining."

The existing passivation layer is not removed, only the iron and iron oxide impurities are removed. Pickling is the treatment that would completely remove the surface layer to a depth dependent on process parameters, leaving a blank, non-passivated surface that would then require passivation before being exposed to corrosive chemicals. This passivation can be achieved with simple air exposure (slow and less effective) or with chemical passivation (faster and more effective).

As for this sentence:

"Citric acid will not remove the existing passivation layer but will only remove the iron and iron oxide residual contamination which makes the layer less effective"

Subject is "iron and iron oxide residual contamination" verb "makes" object "the layer". Sorry if the sentence was too convoluted possibly leading to misunderstandings. Iron and iron oxide impurities can serve as initiator sites eventually leading to pitting corrosion. Their removal leaves an iron-free passivation layer which is much more effective.

 

[RPh_Guy]

"Another benefit of citric acid passivation using CitriSurf® is that the treatment removes only the iron from the surface, and not other metals in the alloy. This affects the depth of the surface treatment and mitigates against changes in the overall size of the part, which can be an important factor in close tolerance and high-precision machining."

The existing passivation layer is not removed, only the iron and iron oxide impurities are removed.

- Citric acid removes only the iron and not the chromium, nickel, or other metals.
- The size of the metallic part doesn't change because the citric acid doesn't remove a significant amount of the metal, only the iron.
- The oxide layer will form passively with air exposure.

I agree with these statements. This what you're saying, yes?

Pickling is the treatment that would completely remove the surface layer to a depth dependent on process parameters, leaving a blank, non-passivated surface that would then require passivation before being exposed to corrosive chemicals. This passivation can be achieved with simple air exposure (slow and less effective) or with chemical passivation (faster and more effective).

Yes, pickling removes more metals than just the iron.

Subject is "iron and iron oxide residual contamination" verb "makes" object "the layer". Sorry if the sentence was too convoluted possibly leading to misunderstandings. Iron and iron oxide impurities can serve as initiator sites eventually leading to pitting corrosion. Their removal leaves an iron-free passivation layer which is much more effective.

Yes, thanks for clarifying.

I think I just misunderstood your meaning of "passivation layer". You're meaning the outer layer of chromium-rich metal surface, and not the layer of oxygen.
We're on the same page now.