finishing.com -- The Home Page of the Finishing Industry
Serious Education & the most FUN
you can have in metal finishing smiley

No popups, spam, registration or passwords
HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
current topics
topic 12028

What is "Pickling" of Steel?


A discussion started in 2001 but continuing through 2018

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.
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.
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.
finishing.com
Pine Beach, New Jersey



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



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.
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.
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.
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.
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.
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.
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.
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.
finishing.com
Pine Beach, New Jersey


< Prev. page       Next page >




If you have a question in mind which seems off topic, please Search the Site

ADD a Comment to THIS thread START a NEW threadView CURRENT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices


©1995-2018 finishing.com, Inc., Pine Beach, NJ   -   About finishing.com   -  Privacy Policy
How Google uses data when you visit this site.