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Passivating Stainless Steel Help


Absinthe Pete

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So the still is finished and installed at my distillery. I'll be posting pics and so forth once everything is setup.

Anywho, the question is I need to passivate the stainless steel still but I have copper in the still that can't be removed. So what can I use to passivate the stainless without hurting the copper?

My rep from Zep Chemicals would normally recommend a blend of Nitric Acid and Phosphoric Acid to passivate the stainless but her lab says it'll turn the copper black and I won't be able to get it back to copper color.

Any help would be appreciated. Thanks.

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There are two highly respected persons in the food grade chemical production industry that can answer your question in seconds. Both of these gentlemen are chemical engineers, not simply salesmen. That being said, they each have their own chemical companies that have supplied the brewing, winemaking, distilling and food processing industries for quite a long time.

Birko Corporation (since 1953): Dana Johnson - 800.525.0476

Loeffler Chemical Corporation (since 1933): Dirk Loeffler -800-769-5020

I highly advise against using general chemical companies to source information from when concerning usage in breweries and distilleries, Zep is one of those. It is best to stick with firms that have significant experience with the special requirements and materials that exist in these environments. I do know of one more brewery specialized chemical provider, but there is nothing in their line that should be used on copper distillation equipment so they were not worth mentioning, particularly to directly answer your question posed here.

Hope this was helpful!

Eric Watson

AlBevCon

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Your post made me google "passivated stainless steel" to learn just exactly what you were asking. I use stainless for the "kettle" component of my process and copper for the "still" component of my process. The equipment was fabricated from a local shop, without mention of passivization. We've used this equipment for 2 years now and have scored 6 awards for our vodka. So I'm tempted to ask, "is passivization really necessary"? The couple articles I skimmed through talked of stainless steel as not stainless until it's passivated. I'm kinda confused myself now with this new info, except for the fact that that our equipment works, the stainless has never corroded anywhere, and the results have been award winning...

-Scott

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Before passivization, first determine if it really is necessary.

Check out : ASTM A380, “Standard Practice for Cleaning, Descaling and Passivation of Stainless Steel Parts" for different passivation AND testing methods.

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Scot, how long do you plan on being in business?

If the answer is more than another year, you'd be well advised to heed MadMacaw's advice and give Loeffler or Birko a call. They'll explain passivation far better than we can, and your tanks will thank you. Pitting and other issues can be invisible to the naked eye until it's too late.

Loeffler is who we use for copper cleaning (Lerapure). Five Star for stainless.

Edit to add--- when I have sold tanks to buy new ones the first question I've been asked is "did you passivate them" ? Food thought, but as always, you have to decide what's right for your shop.

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Your post made me google "passivated stainless steel" to learn just exactly what you were asking. I use stainless for the "kettle" component of my process and copper for the "still" component of my process. The equipment was fabricated from a local shop, without mention of passivization. We've used this equipment for 2 years now and have scored 6 awards for our vodka. So I'm tempted to ask, "is passivization really necessary"? The couple articles I skimmed through talked of stainless steel as not stainless until it's passivated. I'm kinda confused myself now with this new info, except for the fact that that our equipment works, the stainless has never corroded anywhere, and the results have been award winning...

-Scott

Hi Scott,

Stainless Steel (SS) is stainless until some free iron is fused onto the stainless. This happens when SS is machined - During the machining of Stainless Steel (SS) some free iron (from the cutting tools) "clings" to the SS in very thin layers as well as some machining fluids. These prevent the SS from aquiring a thin oxidised layer (which protects the SS and make it "rust-resistant"). With passivization the SS is first cleaned (to remove ALL free iron and grease) and then very thinly "coated"(oxidised) to provide the SS with a stainless surface as it originally was.

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So if I put an award in my still, I'll never have to clean it??? Scott, I hope you consider learning a little more about long term maintenance soon. I use acid no. 5 from Star San with very good results. It can be used as a rinse, cleaner and passivation.

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So if I put an award in my still, I'll never have to clean it??? Scott, I hope you consider learning a little more about long term maintenance soon. I use acid no. 5 from Star San with very good results. It can be used as a rinse, cleaner and passivization.

Ummmm, I didn't "put an award in my still". I was making the point that what comes out the still has been awarded, and more than once for that matter. If that doesn't carry weight for you, then perhaps you are more interested in how I'm considering abandoning my oil-fired steam supply for a mule and waterwheel. But I'll save that discussion for a different thread.

And I 'clean' my stills, thanks. I will refer you to my awards again as proof. You may refer me to your awards too as proof to your process being superior. No need to generalize with a snarky one liner and call it input. If cleaning is now equal to passivization, and passivization is the key to preventing my equipment from turning to dust, then I'm learning something, mission accomplished.

So those that passivize their SS, how do you know you need it, and how do you know the passivization process was successful?

Thanks,

-Scott

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Scott, you'll need to clean first. When you have a clean surface, then you can passivate.

Give one of the two companies mentioned a call. Grab a pad of paper, and take good notes, their advice is free. Your equipment will last much longer, and will hold its resale value should you need larger tanks.

Just trying to help.

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Can of worms meet ADI? LOL Anyway, I'm a welder and have a machine shop so my still was entirely constructed by me which means the areas which were welded have gone through a metallurgical change because of the heat applied. This means that those areas are subject to surface rust if not passivated.

If your tanks are fine and have not rust then they might have been passivated or doesn't need it. Passivation is really only necessary on newly welded items, although any stainless part will benefit from passivation. If the tanks are polished then that helps as a smooth surface is less likely to develop surface rust.

Madmacaw, thanks for the info I'll give them a call tomorrow.

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Could be wrong but I seem to remember from a food engineering course that every time you clean your stainless with caustic and phosphoric (or other acid), you rebuild the passivation layer on stainless. I've sent an email to our local stainless expert.

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Quite funny!! I have many more snarky comments but will try to remain civil!!

Phosphoric can passivate stainless, however you need an elevated temperature and to air dry the metal to achieve passivation.

I've only had one materials engineering class years ago and learned from experience on my equip, I would definitely contact the experts as Eric recommends.

Thanks for the contact info Eric. I will definitely consult with them in the future. I'm going to be building more

equipment soon and have some questions about cleaning up some of my welding mess chemically rather than physically!

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Pete,

There is a machine called a surefox it uses a phosphoric acid solution combined with a small current to passivate welds. We use it in our stainless shop. Its sort of like a brush so you can spot passivate with it. New ones run about $3,000 but I imagine you could find one on ebay or probably build something for cheap. Surefox 203

Passivation is pretty straight forward. Its just a fancy word for creating a uniform oxide layer on metals which protects the bare metal beneath. There are a number of commercial products out there like CIP 100, 200, by Steris, and various other listed in this post. They are all generally made up of some type of sodium hydroxide solution for the first wash and a phosphoric acid solution for the second wash.... inexpensive to make. Wiki has a good article about it http://en.wikipedia.org/wiki/Passivation.

Be care full having bare copper touching bare stainless. In the presence of wash or moisture the stainless will rust over time if its connected to the raw copper in a way that electrons can flow. This is a redux reaction and I have had issues with it in the past - stainless packed copper column = rust. again wiki has a good article on it. http://en.wikipedia.org/wiki/Electrochemistry

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Our cleaning process:

To clean our mash tanks and fermenters we only do two processes after our initial passivation. We clean the grain off with caustic, rinse with fresh, and then sanitize with PAA. We seal the door to the fermenter but leave the drain at the bottom open to drain any residual PAA/water mixture then we pump into that tank within 24-48 hours. Only occasionally do we use acid on our stainless.

For our still we use a caustic solution to remove grain, rinse, then use a citric solution that we strengthen until it cleans it up, then rinse again.

At the top of our mash tank, we do get some haze above the grain line. So anywhere above the mash being mixed, we get some haze which we clean off with acid on an occasional basis, but not everytime.

Denver, how often do you use acid and how often do you passivate?

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We have open top stainless fermenters. We use acid every 3 turns, and passivate a little more than once a year. We're pretty aggressive (relative to distilling rather than SOP for breweries) in our cleaning regime because we're in the process of moving to wooden fermenters, and we know we're going to be unloading almost all the stainless on the used market within the next year.

Cheers

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John, one thing you may want to consider is a period mega-clean where you alternate your hot caustic with a hot acid. The reason being that caustic primarily removes fats and oils, deposited heavily during fermentation, but it's not effective for removing minerals and that's were the acid comes in. Over time you can develop a layered soil deposit in your tanks that won't wash out with caustic because is covered with a layer of minerals. It's built up over time layer by layer so needs to be removed layer by layer (fats, minerals, fats, minerals). You could probably get it done in 3-4 cycles but if you already have a deposit that doesn't wash off it may take more than that for the initial clean.

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Nice advice, Ned.

The one thing that should be remembered is that every plant should come up with a definition of clean, and a definition of sanitized, and a definition of rinsed. We'll all have different choices, and you need to have

a complete understanding of the consequences of our choices. Things like chemical costs, energy consumption, impact on environment, labor costs, metal stress, safety of your workers, etc., all come into play. And again, a phone call to the above number will really help guide your choices. Send them a copy of your cleaning procedures--- they'll be happy to go over it with you.

That said, we're not brewers or vintners. We don't have to come anywhere near the level of sanitation that they do because we're vaporizing what's coming out of those tanks. That doesn't mean that we can't clean that

much, or that we shouldn't. We just have a wider highway to drive on than they do. There are tradeoffs with all ofyour choices.

Hope everyone has a great weekend....

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  • 2 weeks later...

Here's a quote from a Food Engineering prof:

What Is Stainless Steel and Why Is it Stainless?

In 1913, English metallurgist Harry Brearly, working on a project to improve rifle barrels, accidentally discovered that adding chromium to low carbon steel gives it stain resistance. In addition to iron, carbon, and chromium, modern stainless steel may also contain other elements, such as nickel, niobium, molybdenum, and titanium. Nickel, molybdenum, niobium, and chromium enhance the corrosion resistance of stainless steel. It is the addition of a minimum of 12% chromium to the steel that makes it resist rust, or stain 'less' than other types of steel. The chromium in the steel combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide, called the passive film. The sizes of chromium atoms and their oxides are similar, so they pack neatly together on the surface of the metal, forming a stable layer only a few atoms thick.

If the metal is cut or scratched and the passive film is disrupted, more oxide will quickly form and recover the exposed surface, protecting it from oxidative corrosion. (Iron, on the other hand, rusts quickly because atomic iron is much smaller than its oxide, so the oxide forms a loose rather than tightly-packed layer and flakes away.) The passive film requires oxygen to self-repair, so stainless steels have poor corrosion resistance in low-oxygen and poor circulation environments. In seawater, chlorides from the salt will attack and destroy the passive film more quickly than it can be repaired in a low oxygen environment.

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  • 8 months later...

All,

There is some great info in this thread and some unfortunate assumptions and practices I would like to address:

1) You ARE brewers if you are mashing grains, using a wort/wash produced by others or using grain based extracts. All of the same standards including cleaning and sanitization apply. Remember, in the case of washes, garbage in truly results in garbage out. The only possible situation where this can be less important is in vodka production, but then your effort and time swings into distillation where you have to carefully distill the wash to eliminate the bad effects of bacterially contaminated washes. In this case, it is still better to follow the same standards... it will produce a better outcome that is easier to distill from..

2) From my training at Siebel Institute of Technology in Chicago, Weihenstephan TUM in Freising, Germany and VLB in Berlin, Germany as well as experientially:

A. Passivation:

Prior to use all stainless steel vessels should be passivated. Even if the equipment was supposedly passivated at the factory, it is still in your best interest to passivate the equipment anyway. The equipment should be rinsed at ambient temperatures and then cleaned first with sodium hydroxide or potassium hydroxide. Even better results can be obtained using either of the latter which have a chlorinated additive. An additional benefit of the latter is you can clean at ambient temperatures which saves energy inputs and time. After the first step and another rinse (ambient if you did not heat your cleaning solution, the same as the heated temperature if you heated the solution) you can use nitric acid (what the factories use) or a nitric/phosphoric blend. Make sure to look up the proper ration of dilution because it is a stronger concentration for passivation vs. cleaning. After the chemical manufacturer's specified CIP contact time, the equipment should be drained and then allowed to air dry in an acidic state. The last step is to rinse the vessel after it dries (within 24 hours). Your vessel(s) will now be passivated as long as you followed the chemical manufacturer's directions. If there are deviations in instructions from what I outlined above, follow those directions.

B. A Little Bit About Cleaner Types and Effectiveness/Cost

1. Caustic/Percarbonate Cleaners: These cleaners are designed to remove organic soils. They have very little sanitizing powers. There are many standard formulations

available for these cleaners. Most were developed for the poultry and dairy industries. There is a disadvantage to percarbonate cleaners (Five Star's PBW/TST/One

Step and various other trad names). Unfortunately they are hydrophillic (draw water readily). From the moment you open the container, the effectiveness decreases

because of this. This characteristic is readily apparent because the product clumps over time. I had a study from the MBAA (can't find it at this point or I would post it)

that revealed that these cleaners had a steep drop in effectiveness after 6 months. This means as time elapses, you have to use more of it for it to be effective. This is

particularly an issue with PBW because it is one of the most costly cleaners in the industry despite it's formulation being similar to most of the percarbonate cleaners on

the market. Sodium and potassium hydroxide is considerably cheaper and does not have these issues.

Some resources for cleaners: Birko Inc. (National), Loeffler Inc. (National), Brenntag (many regional locations), Rochester Midland (many regional locations), ADM

(some locations) and many independant providers in the dairy and food processing industries. Try to source within your region as the shipping costs can be high due

to the weight.

2) Acid Cleaners: It is best to use formulations that contain both nitric and phosphoric acid. They allow the maintenace of passivation as well as the removal of inorganic

soils. Phosphoric acid alone is a fairly weak cleaner but with nitric acid in the blend, it becomes very effective.

3) Some Temperature Guidelines: Follow the manufacturer's directions in all cases, but the general rules are:

1) Sodium/Potassium Hydroxide: Clean between 140 and 180 degrees F.

2) Sodium/Potassium Hydroxide WITH Chlorine Additives: Clean at ambient temperatures. You can also clean at heated temperatures, but the solution becomes more

agressive and experientially, I and others have found it unnecessary to heat the solution. Chlorinated caustic is inexpensive and is more than 50% more effective

than cleaners without the additive. Some may react to this suggestion with puzzlement. Brewers for many years have been told repeatedly not to allow chlorine to

contact stainless steel. Although this is true, that edict refers to using sodium hypochlorite in a solution alone. If not rinsed really well, this practice can cause de-

passivation, pitting and rusting, particularly at weld lines. Once entrained with sodium or potassium hydroxide and then rinsed per directions followed by an acid

wash, this is not an issue as any residual chemicals are neutralized. NEVER use a chlorinated or non-copper inhibited percarbonate or sodium/postassium

hydroxide cleaner on ANYTHING copper! The results otherwise will cause pitting and degradation of the copper equipment.

3) Cleaning Cycles Should Be Undertaken in Cycles:

The appropriate practices after passivation and first use (Stainless steel equipment only):

1. Rinse all matter from vessels with an ambient water rinse. NEVER rinse during this step with hot water as it may cause the soils to be bound to the vessel's surfaces

making cleaning and sanitization more difficult or ineffective.

2. Perform a percarbonate or sodium/potassium hydroxide cleaning (w/without chlorination) as per manufacturer's directions.

3. Rinse with clean water as per manufacurer's directions. (temperature should be the same as the wash in step 2.

4. Perform an acid wash with a nitric/phosphoric blend at ambient temperature. (see #7 as well)

5. Rinse with clean water at ambient temperature.

6. Leave all valves and manways open to completely air dry until the next sanitization cycle.

Note: If you have interconnected equipment such as that in professionally produced wash production systems which usually have pumps, valves, piping and heat

exchanger(s) all piped together, allow all cleaning solutions to cycle through all of the wash pathways. Heat exchangers must be cleaned in reverse flow to eliminate

the soils accumulated where eddies were created by the wash knockout in the opposite direction. This is achieved by using hose "jumpers" or if included in your

system, a revese flow pathway controlled by valves.

7. The acid wash cycle usually only needs to be employed every 4th cleaning or if inorganic soiling becomes evident. (Stainless steel equipment only)

8. After 4 acid wash cycles, reverse the cleaning regimen, in other words acid wash after the soils rinse, then apply the percarbonate or sodium/potassium hydroxide

cleaning proceedures followed by a rinse. This practice ensures that soil binding potential is reduced. After this application, return to sodium/potassium hydroxide

followed by the phosphoric/nitric blend wash (if in rotation or as needed).

NOTE: For still cleaning:

a. After Low Wine Runs: Rinse with water at ambient temperature. Continue low wine runs until equipment will be dormant for a period or will next be used for

a spirit run. Clean with citric acid until the copper surface areas are restored followed by a rinse. Leave all valves and manways open to allow to air dry.

b. If you notice streaking, soil accumulations or a black/brown film that does not go away after proper citric acid washes, a inhibited caustic or percarbonate

cleaning cycle is necessary. NEVER use un-inhibited or chlorinated cleaners in copper fabricated or containing vessels! Follow this

proceedure with a clean water rinse at ambient temperatures and a citric acid cycle followed by another rinse at ambient temperatures. Leave all valves

and manways open to allow to air dry.

c. For Spirit Runs: You should renew the copper surfaces of the distillation system before every spirit run. This will ensure that the maximum catalylictic

action of copper will be available which will produce the best spirit results.

d. If you experience foaming during a distillation run (applies to mostly to protein containing washes, particularly if conduction on grain distillations): Use an

anti-foam product at the proper dosage. The use of these can also result in higher fill levels in your still. If this proves ineffective (very rare with proper

product selection and usage), you can investigate using enzymes in your wash production that reduce proteinaceous compounds.

e. Most washes tend to foam initially due to entrained carbon dioxide being released as the wash is heated. This cause disappears relatively quickly though

as most washes don't exceed 2% carbon dioxide by volume. Again, the proper use and selection of an antifoam agent will eliminate this issues.

If you are not following any of the above and believe that you are achieving the best possible results from your systems, by all means continue. What has been outlined are industry standard practices that have been in place for a long time and have proven to be effective long term.

Additional notes:

NEVER use anything more abrasive than a sponge (w/o a scrubbing surface) to clean equipment! Doing so will produce swirls and scratches on the equipment surfaces making cleaning less effective (due to soil deposition/bacterial organism trapping). The above listed cleaner are more than adequate to clean the equipment properly with out the need for agressive scrubbing by hand if used at the proper ratios, temperatures and cycle durations.

If you have equipment not equipped with CIP provisions or utilizing open fermenters that require manual cleaning: It is best to use acid anionic sanitizers. These sanitizers are the only group that will sanitized in the presence of proteins. They are best used at ambient temperatures and sprayed onto surfaces with a garden sprayer or spray bottle to all wort/wash contact surfaces. These sanitizers foam and therfore will "stick" to the surfaces of the vessels and enter any irregular surfaces. When using these sanitizers, a rinse is not required. The agents are neutralized upon filling and have no residual effect on the product.

I hope the above information is useful!

Eric Watson

President

AlBevCon LLC, USA

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Folks: Sorry about the odd spacing in the post above, evidently this forum does not react to standard formatting attempts!

Eric Watson

President

AlBevCon, LLC

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  • 3 years later...

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