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topic 12028p2

What is "Pickling" of Steel? p2



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A discussion started in 2001 & continuing through 2017

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
Teds signature
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
Teds signature
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
Teds signature
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
Teds signature
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
supporting advertiser 
Pittsburgh, Pennsylvania
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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
Teds signature
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
Teds signature
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
Teds signature
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,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


October 20, 2015

thumbs up signI 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


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
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


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
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


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

thumbs up sign 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,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


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,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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



Is degreasing before pickling necessary?

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
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"

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



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
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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 actual situation. Thanks!

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


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