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What is "Pickling" of Steel?



Q. I am a student from Strasburg high in Colorado and I was wondering what is pickling steel? I have been looking all over the internet and you are the closest I have gotten.

Thank you,

Luke P [last name deleted for privacy by Editor]
- Strasburg, Colorado, America


 

A. Hi Luke. If you picture the making of steel, you have a red-hot metal that you are forming, rolling, forging, or whatever. The surface of the hot steel is going to react with the oxygen and water vapor in the air, forming something similar to a very heavy rust. This is called 'scale'. The scale needs to be removed, and 'pickling' is usually the name given to the chemical (acid) removal of scale.

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Uses and Composition of Pickling Inhibitor

 

Q. I want to know the uses and composition of Pickling Inhibitor used in the pre-galvanising process of cold rolled steel.

Ishaq [last name deleted for privacy by Editor]
trading co - Jaipur, India


 

A. Hello, Ishaq. Hydrochloric acid is used to remove rust and scale from steel. But hydrochloric acid will also attack and dissolve the steel itself. Pickling inhibitors are interfacially active compounds which bind to the steel as monomolecular layers, and shield it, reducing the attack on the steel. This saves steel, and lengthens the life of the acid.

One way of answering your question about their composition is to say they may contain both organic and inorganic ingredients (according to Surtec, they commonly contain alkenes, alcohols, amines, polymerized aromatics, and heteroaromatics), but they are not a generic chemical formulation; they are proprietary products available under such trade names as Rodine, Akzo and Stannine LTP. Rodine alone has about a dozen different formulations for different situations. Good luck.

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Can pickling be done in the field?

 

Q. I work for a general contractor and I am reviewing the specifications for metal fabrications. The specs call out pickling before galvanization. I understand a little that pickling is a trade name for a chemical used to remove rust. How exactly is this process done in the factory? Can pickling be done in the field (i.e. on a job site)?

Sam Johnson
- Cotapaxi, Colorado, USA


 

A. Hi Sam. "Pickling" is not actually a "trade name" (which I consider to be like a trademark but without discussing the legality of the claim to ownership of the word), it is the name for the generic industrial process of removing mill scale. Often there is a mechanical 'scale breaking' step first, which passes the product through rollers designed to fracture the brittle scale to mechanically flake off what you can, and to offer more surface area for quicker chemical reaction. Then hydrochloric or sulfuric acid dissolves and removes the heavy mill scale before the steel mill ships the material to you.

People adopt shortcuts in their speech, so galvanizers and electroplaters sometimes call the rust removal or activating acid dip before their process "pickling", but it's a semantics issue; it's different and milder than what steel mill personnel would call 'pickling'.

It is possible to do field application of metal cleaning and processing chemicals and there are companies like Astropak and ATP Results, that specialize in it. Good luck.

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Regeneration of pickling liquor (HCl)

(2002)

Q. Hello!

Although I am working in aluminum foundry, I just finished my degree in material science, and I have to make a work about pickling of steel and regeneration of hydrochloric acid. Can somebody help me on telling me where can I find information about this, I found something but is not enough. Also, the uses of the iron oxide that is obtained form the regeneration of pickling liquor.

Thank you in advance.

Carlos E. Ortiz Hernandez
- Ramos Arizpe, Coahuila, Mexico


(2002)

A. We have been regenerating "all" of our acids and rinses chemically for the last two years. You can see the article that describes this in "Products Finishing" magazine (November 2002) page 82.

David C. French
- Charlotte, North Carolina, US


 

Q. Sir, I am a student carrying out a project work on PERFORMANCE OF VARIOUS PICKLING SOLUTIONS ON RUSTY MILD STEEL. Please assist me with the various types of pickling solutions for removing rust on mild steel including their compositions. I will be grateful.thank you

Chris M.
student - California, USA


(2007)

A. Phosphoric acid is sold commercially as Rust Converter [linked by editor to product info at Amazon] or Naval Jelly [linked by editor to product info at Amazon], Chris. This is best for deterring future rust. The more powerful acid for quickly dissolving rust is hydrochloric acid, sold commercially as Muriatic Acid [linked by editor to product info at Amazon], but this leaves the surface extremely active and prone to flash rusting. Sulfuric acid is also widely used; but at room temperature it is only a mild activator -- it needs to be very hot to actually function for pickling. Good luck.

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Environmentally friendly pickling

August 3, 2008

Q. Is there an easy environmentally friendly way to remove pickling from steel to achieve a shiny surface?

Thanks!

Chi

Chi Leary
Artist - C Spgs., Colorado, USA


August 4, 2008

A. Hi, Chi. Pickling is the removal of scale. It's a process, it's not a surface coating, so I don't know what you mean by "remove pickling" -- maybe "remove scale"?

You can get to raw steel via mechanical methods like sandblasting or polishing if you want to avoid acids. But steel is a reactive surface; you can get it shiny momentarily but it is going to rust fairly quickly if not protected. Good luck.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Best sulfuric acid concentration?

September 14, 2008

Q. Dear Sir, I am willing to use H2SO4 as pickling solution for mild steel, what is the best concentration of H2SO4?
Regards

Ahmed Y Musa
- Malaysia


September 14, 2008

A. Hi, Ahmed. The sulfuric acid needs to be heated, of course, so the first question back to you is what temperature are you trying to operate this pickling process at? Some people believe the best economy is achieved by pickling at a relatively high concentration and as the metal builds up, dilute it. It is claimed that the reduction in dissolved metal by dilution overcomes the dilution effect of the acid, so some aggressiveness is restored simply by adding water. Hopefully we can steer you to appropriate books about pickling if you can tell us a little more about your situation.

Good luck.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


September 20, 2008

Q. Thanks a lot for quick reply, what I tried to do is to use a novel inhibitor in pickling process. Different temperatures and different inhibitor concentrations will be carried out in the test. I choose H2SO4 because it's very common in industry. If I use high concentration of H2SO4 then the more O2 dissolved, while low concentration means little effect of H2SO4 in pickling process, Please advice which concentration of H2SO4 I should use? Regards,

Ahmed Y Musa [returning]
National University of Malaysia - Bangi, Malaysia


September 25, 2008

A. Hi. I have heard that everything from 5 percent to 40 percent has been used. But most typical would probably be about 25 percent. Again, some people start out at higher concentration, then add water to get additional life.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Pickling vs. passivation

November 6, 2008

Q. What is the difference between passivation and pickling of steel?

Jerry Jenkins
Aerospace - Ogden, Utah, USA


November 6, 2008

A. Hi, Jerry. The page explains what pickling is, so I won't repeat that part. Passivation is never to my knowledge employed on steel --but you may be thinking of stainless steel? In that case passivation is the removal via acid of any remnants of plain steel that may have contaminated the stainless surface during fabrication operations. Passivation also supposedly chromium enriches the surface of the stainless. The purpose is to prevent rusting and improve corrosion resistance. It's most commonly done by immersion in nitric acid or citric acid.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


Dimension reduction from pickling

January 16, 2009

Q. Hi. When hot rolled steel is pickled to remove rust, how much of the surface is removed? Is it a measurable amount or even noticeable? Many thanks

Albert Weatherill
Surveyor - Hull, Yorkshire, UK


January 24, 2009

A. Hi, Albert. Again we have semantics issues that may lead to misunderstanding. The steel mill removes the scale before they stock or ship the steel to you. So the user is not involved with scale removal, and some will say the user is not involved with pickling.

But during shipping, and during storage before and after shipping, rust will start to build up on the steel and you wish to remove this. Generally an acid dip to remove rust will involve the use of inhibitors to limit the attack on steel, and timing the immersion proportionally to the amount of rust. I can't give you a dimension of how much steel is removed, but it isn't much -- plating shops do rust removal from fasteners before plating them, and it rarely causes any dimensional problems even on fine-threaded small diameter fasteners.

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 10, 2010

Q. I am in the rollforming industry although we typically rollform painted or galvanized steel coil sometimes we roll uncoated steel. When we rollform uncoated steel the progressive bending process produces a fine dust we call mill scale. Does that mean all the mill scale is not completely removed during the Hydrochloric acid removal process or should I seek a new supplier?

Gary Jensen
buyer - Liberty Lake, Washington


December 10, 2009

Q. We want to reduce the iron content in the HCl acid used as a pickling solution in galvanizing plant.Since our sludge generation is more, by neutralising pickling waste with lime solution in Effluent Treatment Plant. Is there any simple / cost effective method available TO REDUCE THE IRON CONTENT IN THE HCl ACID by adding any chemical to precipitate / to settling down.

K . LENIN nadar
engineer - galvanizing - Madhya Pradesh - INDIA


sidebar

thumbsup2Folks! Although it's human nature for more people to ask for help that to offer it, this is a public forum where people help each other out, not a place where I pose as an expert on every situation. I've been the sole responder on 9 questions on this page. If you found this page, you know at least something about the subject -- please try to help the other people out. Thanks!

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


Ah, but Ted, you are responding so well to the questions. What more could I add? You are indeed a good expert!
The only comment I would add is around the topic of acid types & concentrations. HCl/muriatic or H2SO4 could both be used to pickle carbon/mild steel. The concentration ranges are usually kept low (mostly for fuming and health reasons), possibly between 5 - 25% (wt/vol).
As metals build (and discolor the solution), the reaction rate will begin to slow. Raising the temperature for any of these acids will increase the reaction rate (think basic chemistry). These parameters, plus the time in solution, can yield a good, clean, and bright surface. If the parameters are out of control, you might get a non-uniform appearance, etching, or even a dark/smut layer that is unappealing.
Asking for a specific concentration range, temperature, etc., is only helpful if you supply the type of steel (and shape/form) and more info. You might be better off to try a few conditions in a lab first.

Amanda Glass
- Springboro, Ohio, USA


thumbsup2Thanks for the help, Amanda! Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



July 16, 2011

Q. We have thick walled MS pipes (ID 4, 6, 8 inch & length 20 ft) which have mill scale that must be removed. I would like to know what would be the best concentration of either H2SO4 or HCl (whichever is the best suitable for the application) to get the job done with minimum fumes (even after using the pickling inhibitors & wetting agents). Thanks.

Sachin Kanse
- Belgaum, Karnataka, India


August 10, 2011

Q. Does anyone know how large the market for pickling might be for the US?

Doug Vail
Student - Atlanta, Georgia


A. Hi Doug. A guideline for trial lawyers is "never ask a question you don't know the answer to". A guideline for students is, or should be, "never post a question you don't understand".

Are you sure that you understand exactly what you are asking? Do you mean in steel mills only, or do you also mean at galvanizing shops and plating shops, and for field application of pickling solutions to tanks, boilers, and piping in-situ? Are you including pickling of stainless steels, titanium, and refractory metals or just steel? Do you expect it to be expressed in gallons of HCl & H2SO4, or dollars spent in purchases of pickling solutions, or in square feet of product? I'm not really trying to give you a hard time, just emphasizing that if you don't understand the teacher's question exactly, you must get your teacher to clarify it, not ask people to guess what the teacher might have meant. Good luck.

Regards,

pic of Ted Mooney
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Ted Mooney, P.E. RET
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Pine Beach, New Jersey


January 10, 2012

Q. I do have a question about the potential downsides of pickling. We've recently changed our suppliers of P&O A1011 hot rolled steel that we use exclusively for manufacturing purposes. However in doing so we've run into a problem in which the surface inclusions (craters) of the steel seem to resist the painting process we use, which has never been a problem in the past. We've had substantial rejection of product due to the steel rusting underneath the paint. Would it be a waste of time to investigate the possibility of the pickling process of this new manufacturer somehow chemically attacking our paint? Thanks for any help.

Kevin Salenski
- Sacramento, California, USA


A. Hi Kevin. I find that quite unlikely. However, I think it is very possible that your in-house pretreatment system is not able to deal with steel which has been less adequately prepared at the mill. For example, if you are using only a 3-stage iron phosphate before painting, it is possible that the process was adequate for the previously supplied steel but not the presently supplied steel.

Regards,

pic of Ted Mooney
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Ted Mooney, P.E. RET
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Pine Beach, New Jersey


January 18, 2012

Q. Hello, my question is if I'm pickling STEEL with a cathodic process with H2SO4 70% - 80% to high temperature like (80 °C) (30 - 60 seconds) is it possible to change physical properties of material, basically TENACITY? Thank you!

Carolina A
- Colombia


January 19, 2012

A. Hi, Carolina.

Unfortunately, the word "tenacity" did not translate well, so I'm not understanding your question. Might you mean "ductility"? Pickling is basically a surface phenomena which should not have too much effect on the underlying steel, with one exception that I can think of: Pickling, especially cathodic pickling, will introduce lots of hydrogen, and can cause hydrogen embrittlement of high strength steels -- even catastrophic hydrogen embrittlement.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



February 15, 2012

Q. Hi, I am currently doing project of scale flakes on hot rolled coils. The scale normal appeared after some few days after temper mill or when the coils are store at the stockyard. Does the chemistry have an influence in the formation of this scale flake?

Godfrey Matshili
- South Africa



May 17, 2012

Q. Related topic, but a unique situation.
We use ~35% HCL heated to 135 °F with Enthone Actane 32 Inhibitor to remove a burn mark left after heat sealing a glass to to a Nickel/Iron alloy wire (electronic device)
We typically need 45-60 min with agitation to achieve a bright finish on the base metal. We keep the pickle for about 10 days and then decant and refresh, trying to keep some metal ions in solution rather than start from scratch. Recently we have had poor removal rates. We possibly have seen some re-rusting, which I am trying to sort out (maybe rinse water too acidic). Looking to evaluate the HCl concentration of the pickle. It starts at about 1.16 s.g. cold. Can't use this method after the dissolution of metals, right? Also, I have read that titrating for acid concentration is not so simple due to the Ferric Chloride. Would an ISE be the right tool for quick and accurate monitoring? Etch rate test maybe? This process is used prior to Tin plating.
Thanks for your thoughts.

Mike Russo
- Lake Mills, Wisconsin, USA


August 11, 2012

Q. Dear Sir,
We have steel pickling plant using HCl. We have water carry-over problem on both edges of the sheet. We have replaced squeeze rolls many times but failed to remove water contents. Please guide me how can I resolve this problem (the hardness of squeeze roll rubber is between 65 to 70 shore).
Regards

Zafar Majeed
- Karachi, pakistan


12028
August 17, 2012

A. Dear Forum persons, regarding the post asking for help in removing water from the plate after pickling with HCl, we got some problems with this and was solved by reducing the concentration of HCl to 35% and adding some small amount (less then 1% volume of the tank) of a product that the market here calls "Lauril" its kind of a chemical used in soap and shampoo making. it helps in flowing the water but it was in our small metal shaping shop. really don't know if it will help in a steel mill.
Congratulations! for me this one is the best resources in finishing on the web !
Regards from Brazil!

Celio Santos
Arte Na Lata - Aruja, São Paulo, Brazil



November 7, 2012

Q. HI. I AM TRYING TO FIND OUT WHAT HRPA STANDS FOR. I KNOW HRPO IS HOT ROLLED PICKLED AND OIL BUT I DON'T SEEM TO FIND WHAT KIND OF FINISH IS HRPA.

LUIS MONTESDEOCA
IMPORT/EXPORT - laredo, Texas


November 7, 2012

Hi, Luis. It could be anything -- including a simple typo. Slang and acronyms are not specifications, and if they don't have a general meaning that is instantly and widely understood, and saves us time, then they have no meaning at all. If a couple of minutes of googling gets you nowhere (and it got me nowhere), the acronym is meaningless and must be spelled out. Good luck.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


April 23, 2013

A. Luis, I can't swear to it but likely HRPA = Hot Rolled Pickled Aluminum Killed.

Kevin Carroll
- Long Beach, California



November 15, 2012

Q. Hi,

I learnt that chelating agents like EDTA and oxalic acid are able to dissolve iron (III) oxide. Using this concept, I intentionally create a dark layer of oxide scale on the surface of a low alloy steel specimen by cooking it in an oven at 650 °F for 2 hours. Thereafter, I carried out several pickling tests by dipping the scaled surface with aqueous solutions of EDTA and also with aqueous solutions of oxalic acid, but the iron oxide scale still remained and do not seem to be dissolved in the same way as when dipped by a hydrochloric acid solution.

I had tried several concentrations of oxalic acid and EDTA until the saturation point, but to no avail. Do I need to modify the test such as by heating up the aqueous solution or by adding some form of catalyst which may help to lower down the activation energy before the iron oxide can be dissolved?

Many Thanks for your advice.

Regards

Lim Ronnie
- Singapore



November 23, 2012

Q. I wanted to know the composition of waste pickle solution. Is it mostly comprised of Fe2+ or Fe3+?

Prabath Gunasekara
- Colombo, Sapugaskanda, Sri Lanka


November 26, 2012

A. Iron dissolves as Fe 2+, but can be slowly oxidized by atmospheric oxygen to Fe 3+. However, as long as the bath is still being used for pickling, any Fe 3+ will be converted back to Fe 2+ in a reaction that dissolves more iron.

Lyle Kirman
consultant - Cleveland, Ohio



December 11, 2012

Q. Dear sir,
I am doing a project to find out the retention time for pickling with HCl. I am considering concentration, weight and section in this.
Do I have to consider any other parameters?
Is there any instrument or method to find out surface cleanliness?
Is there any instrument or method to find out quantity of rust on a material?
Is there any projects , paper or any kind of literature about retention time for pickling which would help?
Please help.
Thanks in advance.

Sharath Bhat
- Jaipur, Rajasthan, India


January 19, 2013

Q. Suppose 23t (avg.) hot rolled coils are pickled in a push pull type continuous pickling line. The coils are mainly for auto industries. When should the acid be changed for good surface finish and better quality? I want to know what should be the frequency to change or top up acid or fresh addition of acid should take place in the acid tank of pickling line. e.g. after 8 coils or 10 coils or 12 coils, etc. Is there any thumb rule? Please help me.

Siddhartha Mukherjee
- Kolkata, West Bengal, India


January 22, 2013

Q. I want to know when should we change the pickling liquor? Is there any clear way to check the quality of pickling liquor?

Regards

Anuj Roperia
student - Chandigarh, India


January 1, 2013

Regeneration of HCl Pickling Liquor

A. Hi Anuj. I could say "don't ever change your pickling liquor". But then you would say "but it gradually loses effectiveness". Then I could say "okay, then change it when it loses too much effectiveness". Then you would say "how much loss of effectiveness is too much?" Then I could say "how much is too much for you?" ...

There are books that try to help you answer the question. It's a difficult question! Short of ordering an automated acid management system or studying books about the topic, I think the only other answer is that you have to start acquiring data comparing pickling time to rejects to costs of regeneration or replacement of acid and adopt a hypothesis and strategy, and refine it over time. Sorry that there is probably no quick answer.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



January 20, 2013

Q. Hi,
in MS pickling process, will we have any change in the hardness of the surface?

DIPAK PRAJAPATI
- Ahmedabad, Gujarat, India


January 21, 2013

A. Hi Dipak. To my knowledge mild steel is not hardened or hardenable, and hardened steel is not pickled, so I don't quite understand. Certainly, the mill scale and garbage on an non-pickled surface would lead to unreliable hardness readings. But please try your best to explain your actual situation rather than posing your question in the abstract, with the countless "ifs ands & buts" that result :-)

Thanks.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


January 26, 2013

Q. In mild steel pickling, we use hot rolled coil. I want to know is there any change of hardness of coil before & after pickling?

In our process, when sheet is passed through concentrated HCl tank, it shines; but after passing through water tank, sheet is yellowish. How can we handle this problem?

DIPAK PRAJAPATI [returning]
- ahmedabad,gujarat,India



A. Hi Dipak. I already tried to answer your first question, and I'm still not quite understanding. Why don't you simply measure the hardness before and after pickling and you'll know the answer for your situation for sure rather than asking for continuing guessing. Further we still haven't been told "why" you ask this question, which limits people's ability to read between the lines to help you out.

I suspect that your pickling acid leads to very rapid flash rusting, accounting for the yellowish appearance. I believe you should have inhibitors in the pickling acid, and then almost instantly get the steel to an alkaline state. Good luck!

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


May 11, 2013

Q. Thanks for your answers. It is refreshing to find real answers, so many sites just have half baked opinions.

I have a small project, steel weldments about 1 ft x 1 ft x 2 in, 20 pieces. Thin material is 0.065 in. These will be used in a wet environment, so I want to pickle before applying a good coating.

I plan to dip in HCl solution, followed with a tri-sodium phosphate neutralizing dip. Are there any readily available inhibitors available to protect the steel? Do I need to use inhibitor? Any suggestions would be useful.

Thanks for your help. I am no chemist, but an established Mechanical Engineer, so if you ever need anything in that arena please ask.

Fred Rosse
steam engineering - Princeton, New Jersey, USA


May 13, 2013

A. Thanks Fred. You are sort of on the right track but not precisely. If you were doing this commercially, you would want to apply an iron phosphate or zinc phosphate coating before painting. It is the phosphating, not the acid dip portion of it, that affords the corrosion protection.

For a simple small-volume one-time operation, I'd use the tri-sodium phosphate first, as a cleaning solution. If you can scrub with a tampico brush rather than just dipping, that would be better. Then rinse and apply a consumerized iron phosphate coating like Ospho [linked by editor to product info at Amazon].

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


May 15, 2013

Q. After pickling mild carbon steel, it has a red tint to it. It doesn't affect any further processing operations, but some customers don't like the fact that it looks different. Any idea what could be causing it?
We use HCl pickling solutions as well as H2SO4. It happens more on the HCl line. We try to re-clean and it usually helps but would want to eliminate this problem. On rare occasions if HCl doesn't clean it the sulfuric would do it.
Also one grade in particular (52100) almost all of the time turns out to have a greenish surface.
Thanks for your help.

Jake Zervas
- Chicago Illinois


July 2, 2013

Q. I am an Electrical Engineer at a Steel Mill and I was given a project pertaining to pickling with HCl. What are the causes of flash rust/stain directly after the strip exits the acid tanks.

Thank you,

John Dockson
- Joliet, Illinois, United States


July 4, 2013

A. Jake, John,

The discoloration (red spots) appear because the HCl is an active etcher (etching goes in active phase). That is why not only oxides are removed from the surface, but the iron from the steel is impacted, and the red iron oxides are formed. It is not good for the steel part, because besides local formation of the rust, hydrogen (from the reaction) penetrates inside the steel surface, and cause local weak points for the metal strength.

"Passive" etching means that only oxides on the surface are impacted, and the actual metal does not react to the etching solution. And the hardness is not changed.

adv.
Contact us for suggestions on how to clean/etch carbon steel.

anna_berkovich
Anna Berkovich
Russamer Labs
 
Pittsburgh, Pennsylvania



July 4, 2013

A. Hi John. Flash rusting is the natural state of affairs . . .
First, the acid and rinse water has iron dissolved in it which cannot remain dissolved as the solution evaporates, but must become rust. Second, the surface is extremely active, in acid condition, and activated by corrosive chlorides. As a minimum you must immediately rinse well and get the material into rust preservative or, at the least, into an alkaline condition. Good luck.

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


August 17, 2013

Q. Hi,
After pickling of Hot Rolled Coils with HCl and rinsing, we want to dry the HRC before re-coiling. What should be the max. temperature of the air that we will use to dry the surface of the Hot Rolled Coils?
Regards,
Hakan

Hakan TURKMEN
- Bucharest, Romania


August 31, 2013

A. Hi Haken
If you use heat you will have to heat up the whole of the metal strip. This is very expensive and slow.
You should consider passing the strip through an air knife to blow off the water.
However you dry the steel it will be very susceptible to surface rust. You may wish to consider a light coating of a rust inhibiting oil if the coils are to be stored for even a short time

geoff smith
Geoff Smith
Hampshire,
       England



September 4, 2013

A. In order to dry the steel, it is usually easier to heat the final rinse and then dry it with unheated air, than it is to dry it with hot air. The high heat capacity of the metal and low heat capacity of air makes drying with hot air difficult.

In order to avoid "flash" rusting, the final rinse must have a very low chloride concentration. Some companies specify <5 mg/L of chlorides. Others add a corrosion inhibitor to the final rinse.

Lyle Kirman
consultant - Cleveland, Ohio



January 15, 2014

Q. Hi,

We are using HCl in pickling and have problem of the bath getting ineffective quickly over time, as the iron content increases. Usually our practice is to get fresh bath done with 30% HCl, added with water in 60:40(acid) proportion .
Also problems faced are heavy fumes (we have avoided inhibitors as we are told that it slows pickling). Our product is 12 to 20 mm thick. Initial pickling time is 10 minutes which goes up to 90 minutes - which is unacceptable to our cycle time

How can we achieve fastest pickling by avoiding iron content generation which spoils bath?

Sameer Nayak
- Belgaum, INDIA


January 17, 2014

A. Hi Sameer. I think you may be misunderstanding the word "inhibitor". This is not a fume suppressant, but a material that helps prevent the acid from being wasted in dissolving steel instead of rust. Using an inhibitor is how you deter the iron content from rapidly building up. Good luck.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Stop flash rusting by neutralizing HCl on pickled steel?

February 3, 2014

Q. After pickling steel with hydrochloric acid, would a solution of methylated spirits and lime be suitable for removing any unspent pickling solution from the steel and stopping flash rust?

Ilk Fish
- brisbane, queensland, australia



Is the use of HCl in decline?

June 12, 2014

Q. Hello Sir,

As per my understanding and research, the use of HCl in steel pickling is witnessing a decline and is expected to continue in this trajectory in the coming years. Could you please comment on that or let me know any possible reasons for the same? It would be much appreciated.

Regards

Abhay Chawla
- New Delhi, India


June 2014

A. Hi Abbay. Do you feel that this decline is due to less steel production, less pickling of the steel, or a switch to substitute pickling agents? Please share what you believe you know on this subject.

My experience on this site is that if you tell people what you think you learned and where you learned it, they will usually comment on it. But if a question is posed in a fashion which seems to show an unwillingness to share, or which implies hidden trump cards you might play to make them look stupid after their reply, it usually attracts less participation:-)

Thanks!

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


June 16, 2014

I believe it is due to greater regeneration and use of spent acid. Do you think it is causing a decline in the use of virgin HCl for steel pickling? Also, are there any new/recent alternatives to HCl that are gaining significance in steel pickling?

Abhay Chawla [returning]
- New Delhi, Delhi, India


June 2014

A. Hi again. I (and most of our readers) am from the metal finishing industry rather than the steel industry. My direct experience in steel pickling is very limited, but I think that decades ago a strong movement from hot sulfuric acid to cold hydrochloric acid took place and that people are not going back ... and I know of no other substitutes. I suppose it's possible that scale-breaking machines have improved, allowing better mechanical removal, which reduces the need for chemical removal though.

I also believe your hypothesis that regeneration and better acid management science has reduced the need for virgin material, and suggest that you contact companies like Scanacon for the perspective they may be able to offer on this factor. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Testing the pickling procedure on sample pipe spools before committing to the procedure for the plant?

October 1, 2014

Q. I am working on epc company. Our client commented that there shall be testing first of pickling procedure on a sample weld of stainless spool pipe. This is to check the performance of pickling acid solution proposed and ensure that it was working well with no issues on weld joints. This is to avoid any problems on the equipment during the pickling and passivation.
However, in normal practice, do we need to perform testing first? What will be the bad effect of over pickling due to high concentration of acid, and what shall be do if that will happened? thanks.

Gee Dec
- Manila, Philippines


October 2014

A. Hi Gee. "EPC" = Engineering, procurement and construction? It sounds like there is or will be a plant with a lot of stainless steel piping that must be pickled, passivated, or in some way cleaned & prepared for service? Your client is certainly wise to want to see the effect of the procedure on a sample of the pipe before exposing all of the pipe in the plant to an untested procedure :-)

But there are specialist firms which travel from plant to plant to undertake this cleaning/pickling/passivation before commissioning and it might be a good idea to retain one rather than hazarding the plant to inexperienced hands. I don't personally know the procedures though.

Regards,

Ted Mooney, finishing.com
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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



September 8, 2015

Q. Hi, we purchase wire for cold-heading production. We sometimes see the low carbon wire (1006-1010) look dark colored on the surface. The wire is pickled in phosphoric acid and then a coating of lubricant is applied. Can these solutions penetrate the steel and change the surface color?

Dan Watson
- Tyrone Pennsylvania


September 2015

A. Hi Dan. Certainly acids and lubricants can change the surface color, but no, they do not penetrate the steel (I'm not sure if I understood the question).

Regards,

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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


October 20, 2015

thumbsup2I run a pickle line that uses hydrochloric acid to pickle. I would be happy to answer any questions on the process as I understand it. Our line was manufactured in the 60's or 70's but we do have some modern upgrades. I would like to compare our process with other HCl pickle lines that are more modern.

Matt barnes
- Warsaw, Kentucky, usa



Acid Pickling Process to remove HR scale

October 21, 2015

Q. Hi,
We have MS HR sheet of 5 & 6 mm thickness; before further process we want to remove its HR scale. For which we require detail acid picking process with all chemicals, temperatures, and process.

Harshal Adep
Manufacturers - Ahmednagar, MH, India
  ^- Privately contact this inquirer -^


October 2015

A. Hi Harshal. I think you should buy pickled and oiled steel rather than trying to start with steel which has hot rolling scale on it. Steel mills usually include mechanical scale-breaking operations before pickling, and it may not be practical to remove such scale by chemical means alone regardless of which acid you use :-(

Good luck.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


October 25, 2015

A. Harshal, on the pickle line at my plant we use a flattener to break mill scale and correct poor shape. If the guage is under .170, we also use a tension leveler. The HCl alone will not remove all mill scale. Our flattener fractures it so the acid can get underneath. The main purpose of the HCl is rust and carbon removal.

Matt barnes
- Warsaw, Kentucky, usa



Is "pickled and oiled" safe to eat off of?

December 18, 2015

Q. I am looking to acquire a piece of steel plate to use as a platform for baking pizza. I came across a source for "pickled and oiled" steel sheets. Is there any problem with using pickled and oiled steel for that purpose? Or does that process embed the steel with anything that would make it unusable for cooking purposes?

Steve Altschuler
- Yorba Linda, California, USA


December 2015

A. Hi Steve. The "oil" would most likely be a hydrocarbon oil, and oil is poisonous. But I don't see any reason you couldn't patiently remove the oil with hot water, detergent, pumice, and a scrub brush.

When it is free of oil it will be "waterbreak-free", i.e., you'll see a smooth layer of water over the whole piece, with no beading or dry areas. After cleaning and testing for a waterbreak-free surface, you can oil it with mineral oil.

Of course, going to a plating shop and getting the piece nickel plated or tin plated would be even better^possible as well :-)

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


December 21, 2015

A. Good day Steve.

Ted has given very good advice on cleaning the steel, but I disagree with the nickel plate, as I think it will eventually wear/flake off based on the baking/temperature/use cycling. Why not "season" the steel as you would a cast iron frying pan?
Buon appetito!

Regards,

Eric Bogner, Lab. Tech
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada


December 2015

thumbsup2 Hi Eric. On second thought, you're right that seasoned steel would probably be all around nicer than nickel plating.

But nickel plating will never flake off in an oven if done properly. Continuous casting molds for red-hot steel are nickel plated, and flaking of the plating would cause a seizing failure that can be a dangerous calamity costing hundreds of thousands of dollars, so they make sure it doesn't happen :-)

Regards,

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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


sidebar December 22, 2015

Good day Ted.

It pleases me to know that I have my head screwed on!
Yes, you are correct regarding adhesion, if done correctly.
I have processed SS automotive bulb shields with Wood's Ni, Semi Ni, bright Ni, microporous Ni, and chrome. Adhesion was always an issue with 55 ft2 work load, loose contacts, etc. We baked 100% @ 650 °F for three hours to check for blisters/ adhesion, chrome show, etc.
It is of my opinion that Ni for oven racks is suitable, because the food for baking is not in direct contact with the grill. But the pizza would be. Good idea?

Happy Holidays and best wishes for the New Year!

Regards,

Eric Bogner, Lab. Tech
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada


December 2015

Hi Eric. Merry Christmas.

It's harder to get good adhesion on stainless than on steel, but Dini's "Electrodeposition" shows some fabulous adhesion even on stainless.

Although I designed & started up hundreds of plating lines, and probably visited over a thousand plating shops over the decades, I never personally plated anything beyond pennies & keys for kids' science classes :-)
I'm pretty much limited to book knowledge on plating processes :-)

Regards,

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Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



January 7, 2016

Q. Hello sir,
Please suggest a good book on Fumes/Gas scrubbing system design for steel pickling plants.

Parag Patil
engineering - mumbai, maharashtra, india



February 10, 2016

Q. How does degreasing before HCl acid pickling help to get better pickling performance, and is it mandatory for say Hot Rolled sheet freshly coming from steel plant?

What should be the optimum relation between HCl acid concentration vs. dip time? Say we are getting same appearance at two combination- dip time 40 min in 5% HCl and 20 min in 10% HCl, both are accepted from our productivity aspect, but is there any other issue with more dip time?

ARIJIT DAS
- JAMSHEDPUR, JHARKHAND, INDIA


February 2016

A. Hi Arijit. In a metal finishing shop, degreasing always precedes acid activation (assuming sandblasting is not done as a substitute for both). The reason is simply that the parts can be expected to be dirty and oily, and acid immersion does not clean them properly.

When you speak of 20 to 40 minutes pickling time, it sounds like you are talking about scale removal at the steel mill (which I'm not very familiar with) rather than removal of light rust, and acid activation in a plating, galvanizing, or metal finishing shop because your immersion times are 10 to 50X as long as I'm accustomed to.

But if you are free to vary your pickling time, it seems that starting with a short immersion time in strong acid, then lengthening the immersion time as you dilute the acid through use would make the most sense. I'm not aware of subtle deleterious effects from too short or too long immersion times as long as the pickling is sufficient and there is no etching/pitting.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

Thought for the day: Rule #7, Give Back to Society -- Ratan Tata


March 29, 2016

A. Hello Mr Arijit,

Why degreasing? Because acid does not dissolve grease or oils, and they (oils and greases) BLOCK the acid chemical process in the parts we put in there. They act as masking agents, so we could get some black spots in the next process because the pickling process was not rightly done, the metal was not activated, etc.

We do not know which process you do to the metal sheets, but I assume it is phosphatizing or galvanizing/electrodeposition. All need pickling to remove scales from the first rolling, and if the rollers were lubricated, you need to remove the oils and greases.

Hope I answered your question!

Best regards,

Daniel

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina


August 17, 2016

I do not comprehend why in this day and age companies dump acid because of metals and organics saturation.
1. Put 1% PRO-pHx [acid extender] into the acid tank that you wish to eliminate the disposal of.
2. Filter your acid with any type of filter you chose. Small tanks often use a FloKing style pump with a 20 Micron cartridge to capture the organics and metals.
3. Check your acid strength at least weekly. Add new acid to keep the bath strength at optimum. Add 1% PRO-pHx based on the volume of acid added.

David French
- Charlotte, North Carolina



Continuous bands of "water stain" like discoloration from HCl pickling line

August 29, 2016

Q. Hello,
We have a turbulent HCl pickling line in our process and the final product of this process is cold rolled automotive high surface quality end-use coil and sheet.
For some mechanical properties improvement, we increased the finishing and coiling temperature; and after this change we have two bands on strip that are unregulated wave shape with yellow color (like continuous water stain) -- the shape of bands is exactly like entrance scale to pickling line.
These bands are detectable in entrance of tandem mill and is strong enough that we can see it after mill, batch annealing, skin pass and finally in finishing line.
Please share any idea or experience about above matter. (Before, I believed that we shall do some main action in pickling line.)
Thanks so much.

ehsan nv
- isfahan, iran


September 6, 2016

A. We always use DI water in the final rinse. It is important that the chloride concentration is less than 5 mg/L to prevent flash rusting.

Lyle Kirman
Consultant - Cleveland Heights



Storing pickled steel

September 14, 2016

Q. Can pickled and oil steel re-scale after a period of shelf life?

william embry
production manager - Marion Indiana usa


September 2016

A. Hi William. Pickled & oiled steel can certainly rust and corrode. Whether it can "re-scale" is a semantics question -- I would not call it scale no matter how corroded it got, because I personally reserve that term for what happens when red hot steel is exposed to the atmosphere -- although I suppose that others might use the word in other senses. But please don't keep it an abstract question -- tell us your situation and what happened or what are actually concerned about. Thanks.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



November 8, 2016

Q. Hi,
How many times a steel can be immersed in pickling bath? And what are the benefits & demerits of it?

Durai Karthikeyan
- Doha, Qatar


November 2016

A. Hi Durai. 7.3 times :-)

Please take a minute to read my request, immediately above, about abstract questions being unanswerable, and tell us your own exact situation. Thanks!

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

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