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topic 12028

What is "Pickling" of Steel?



A discussion started in 2001 & continuing through 2017

(2001)

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


(2001)

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



Uses and Composition of Pickling Inhibitor

(2002)

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


(2002)

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



Can pickling be done in the field?

(2004)

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


(2004)

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



To minimize searching and offer multiple viewpoints, we combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition.



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


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



(2005)

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


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
Teds signature
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
Teds signature
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
Teds signature
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
Teds signature
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
Teds signature
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
Teds signature
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

thumbs up signFolks! 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 try to 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
Teds signature
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


thumbs up signThanks for the help, Amanda! Regards,

Ted Mooney, finishing.com
Teds signature
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. We've all heard the guideline for trial lawyers: "Never ask a question you don't know the answer to". A guideline for students is "Never post a question you don't completely understand".

Do you understand exactly what you are seek? Do you mean in steel mills only, or do you also mean at galvanizing shops and plating shops; how about for field application of pickling solutions to tanks, boilers, and piping in-situ? Pickling paste for weld areas? Are you including pickling of stainless steels, titanium, refractory metals, cast iron and aluminum castings, 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 really not trying to give you a hard time, Doug, just trying to emphasize a lesson for students that if you don't understand the teacher's question exactly, you simply must get your teacher to clarify it ... hoping that people's answers will clarify your question never works, it just embroils you in Chinese Whispers. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
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 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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
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
Teds signature
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
Teds signature
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


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