Citric Acid Tek: gotta keep em passivated

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so, you want passivate your stainless, but don’t know where to start?

me too… I actually called every welding supply in town yesterday, and not one had any clue what passivation was…which made it much harder to purchase the supplies.

what IS passivation? and why do I care?

…and then?!?

yeah, no clue yet. need to track down supplies for flushing, washing, then passivating. Duratherm claims they have good success using isopropanol to flush systems of Duratherm S, so chances are I’ll start there…just not sure what I want to use for the “wash” step.

then on to the citric acid.

looking for advice/tips.

planning on documenting the voyage in case it’s useful to anyone else.

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Following this closely! I need to passivate my steel too. That’s why I was pestering the bizzybee rep about electro polishing

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I believe this may be similar to stainless weld cleanup systems/tooling. If so, I’m pretty sure I’ve got a couple of acceptable looking diy type resources on the topic hiding in my files. I’ll see what I can dig up for ya.

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You thinking of going the nitric/phosphoric acid route or the citric acid route?

I’ve got some 200L solvent tanks I need to do this to.

Nvm, I see the post title now. Lol

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Wouldn’t something like starsan and pbw help with washing @cyclopath?

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possibly. those are both aimed at removing brewery residues from tanks. PBW strikes me as similar to alconox, and starsan looks like a less aggressive version of the acids to be used for passivating.

I’m leaning towards flushing with iso, then washing with hot alconox, rinsing with water, then switching to hot citric acid. still have more reading to do. also hoping that if I give it a few more hrs, someone with actual experience will chime in and share with the rest of the class

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Can the citric acid be used again?

Are you going to make a bath or recirculate it through the system another way?

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hoping to recirculate.

No clue on reuse.

Iso, alconox, and water are all good to go in my circulator.

still dubious on 0.6M citric acid at ph 3.

Not sure I actually care enough about the pump to worry about it…so I might should wait till the boss is back in town before pushing go on the acid wash.

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This is the DIY version of a stainless weld cleaner, which would likely do the trick for what you’re looking to do, but would almost certainly be a fuckton of work relative to a pumpable liquid process.

Here is a pretty interesting article on liquid phase passivation for those following along at home. Comes with recipes and everything. Seems like it should be reasonably simple.

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Yeah, it’s been documented that I’m lazy. All this is going to be performed insitu, using the circulator.

Turns out the boss has the same opinion on the pump in question as I do, so I’ll be pushing go on this shortly.

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Passivation is simple. You apply an acid solution to your stainless, and use a current to transfer the chromium to the surface layer of the stainless.

Using phosphoric acid Is the safest and most common solution for passivation.

Passivation should ONLY be done by trained Welders whom have knowledge of the method of action, safety precautions, have appropriate PPE, tools, etc…

This is not something you can simply do in a shop and expect to come out well…

My shop has literally invested over $50k to be able to properly work stainless; welding, fume mitigation controls, PPE, Passivation equipment, etc…

Most welding shops will not bother to invest in passivation equipment. Not enough people weld stainless and need it done to sanitary spec.

Be safe if you’re going to DIY. Gloves, goggles, and a respirator if it’s a strong acid solution.

Always neutralize and clean your parts after.

Using DIY with common acids, your stainless final finish may not look as nice as electropassivation finishes look.

Residual chromium residue will be present and needs to be cleaned and disposed of properly.

We run a Cougartron at my shop, with phosphoric acid.

Most people stay away from nitric/pickling acids, they are nasty and fuck your system up quickly if you are not properly PPE’d up.

I would suggest trying to use vinegar/acetic acid, and a soft abrasive brush. If they does not take off your oxidized layer, move to CLR.
If that still doesn’t work, you may indeed need a passivation/polishing pass with acid and an electropolishing device.

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Issue in this case is presumably INSIDE my jackets. So whipping out the electrickery isn’t gonna get the job done.

Chances are this won’t accomplish a whole lot either, but it’s what I’ve got, and it shouldn’t hurt the equipment.

Appreciate the “don’t try this at home”, I’m working under the supervision/tutorledge of a welding INSTRUCTOR, one who is called in to do the sanitary welding at Ninkasi when their in-house guy is out of his depth.

He has also done work on the stills over at heritage

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I’m getting my citric acid and drain cleaner from Wally World, it’s not like I’m making D8 with it…

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I’ve heard of this from my welding buddies and appreciate the knowledge. What I don’t like is now The Offspring is stuck in my head this Friday afternoon.

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perhaps I can substitute Julie Andrews and Mick Jagger singing rounds?

I feel sticky, oh so sticky…

I know it’s only BHO, but I like it…

Which is a more tradition Friday afternoon refrain.

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Italics aside, commercial bakery supply vendors are a great source of bulk citric acid if one requires it.

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Did you get new stainless or are you repairing/creating new pieces? I saw where it was on the inside of a jacket and I assumed a repair.

Reason I ask. We have done some stainless welding, just nothing on parts that will touch solvents or oil. The shop that does our welding where solvent and oil touch the welds, were treated (passivized) by the shop.

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See:

Or just sing along with Julie…

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Breweries have to passivate their tanks, I’d suggest looking into that industry for guidance. CMG has a quick write up on it here.

https://countrymaltgroup.com/what-is-tank-passivation/

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@NicksPicks not trying to nitpick but afaik there’s no requirement that they passivate fluid paths for heating/cooling liquids or steam, just the surfaces that may come into contact with what they are brewing or distilling.

I really like the electrically accelerated passivation strategies I just wonder how realistic it is to do inside of a tank jacket that doesn’t have a clear path to stick an electrode brush in

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Process chemists and plating companies do this all the time. It can be pricey.

EDIT: Misread your comment. I think the most simple way to passivate a jacketed vessel is full-immersion into a bath.

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