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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 u,
Luke P [last name deleted for privacy by Editor]- Strasburg, Colorado, America
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Q. I want to know the uses and composition of Pickling Inhibitor used in the pre-galvanising process of cold rolled steel.
Ishaqtrading co - Jaipur, India
A. Hydrochloric acid is used to remove rust and scale from steel, Ishaq. 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. Good luck.
Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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. "Pickling" is not a trade name, Sam, 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'.
Ted Mooney, P.E.
finishing.com
Brick, New Jersey
Q. Sir, I am a student carrying out a project work on PERFORMANCE OF VARIOUS PICKLING SOLUTIONS ON RUSTY MILD STEEL. Pls, 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. Good luck.
Ted Mooney, P.E.
finishing.com
Brick, New Jersey
August 3, 2008
Q. Is there an easy environmentally friendly way to remove pickling from steel to achieve a shiny surface?
Thanks!
Chi
Artist - C Spgs., Colorado, USA
August 4, 2008A. 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 pickling 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.
Regards,
Ted Mooney, P.E.
finishing.com
Brick, New Jersey
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? Rgds
Ahmed Y Musa- Malaysia
September 14, 2008A. Hi, Ahmed. The sulfuric acid needs to be heated, of course, so the first question back to you if 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, P.E.
finishing.com
Brick, 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 MusaNational University of Malaysia - Bangi, Malaysia
September 25, 2008A. 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, P.E.
finishing.com
Brick, New Jersey
November 6, 2008
Q. What is the difference between passivation and pickling of steel?
Jerry JenkinsAerospace - Ogden, Utah, USA
November 6, 2008A. 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, P.E.
finishing.com
Brick, New Jersey
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 WeatherillSurveyor - Hull, Yorkshire, UK
January 24, 2009A. 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, P.E.
finishing.com
Brick, 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?
buyer - Liberty Lake Washington
S | Folks! 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 :-)
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July 7, 2011
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.
- Springboro, Ohio, USA
July 7, 2011
Thanks for the help, Amanda!
Regards,
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 Ted Mooney, P.E. finishing.com Brick, 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 VailStudent - Atlanta, Georgia
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
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. 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, P.E.
finishing.com
Brick, New Jersey