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Pickling of Steel Q&A's




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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 17, 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


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 Heights, Ohio



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 15, 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
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




Stop flash rusting by neutralizing HCl on pickled steel?

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
February 3, 2014




Is the use of HCl in decline?

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 12, 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 be more willing to comment on it.

Thanks!

Regards,

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



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


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 rather limited, but I think that a couple of 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 3rd choice. 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
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




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

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 1, 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
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




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 8, 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
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



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

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 21, 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
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


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?

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 18, 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 [on eBay or Amazon], and a scrub brush [on eBay or Amazon].

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
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


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



thumbs up sign Hi Eric. On second thought, I'd agree 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
Striving to live Aloha
finishing.com - Pine Beach, New Jersey



sidebar

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



thumbs up sign 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 many hundreds of plating lines, and probably visited well 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
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




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

Parag Patil
engineering - Mumbai, Maharashtra, India
January 7, 2016




Is degreasing before pickling necessary?

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 10, 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
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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

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 Montañés
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina




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

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
August 29, 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

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

william embry
production manager - Marion Indiana usa
September 14, 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
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




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 8, 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
Striving to live Aloha
finishing.com - Pine Beach, New Jersey




Q. Hi,

I am working in foundry with supplying casting which go through pickling process.
We are facing some problem where after pickling process, there is lots of black dot appear on the casting surface.

May you advice what is the possible cause that cause such defect?

I also been through in internet saying some casting require to go through a cleaning process before proceed with pickling process. Is it really necessary?

Thank you.

Best regards,

James Chua
- Seremban, Malaysia
February 24, 2017


A. Hi James. Yes it is really necessary. Myself and Daniel already offered our answers to that question on this page. Please refer to them and expound on your question if your think our answers didn't quite cover your situation. Thanks.

Regards,

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



Q. Hi Ted,

Thank you for your guide.

Just to clarify, we are producing casting instead of Hot Steel Rolling which will have oil/grease, and our casting is going through a steel ball shot blasting before proceeding to the pickling.

After review to the related respond, may I know besides the oil/ grease which can cause the black spot; is there any other possible reason which will also causing similar situation?

Thank you.

Regards,

James Chua [returning]
- Seremban, Malaysia


A. Hi again James. Scrub a few with a pumice solution and a tampico brush (or toothbrush depending on size of the parts) and let us know what happens when you pickle them.

In general though, I don't think I'd be surprised to see carbon spots on cast iron after pickling.

Regards,

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


A. Hello James!

I think you can try the following:

- Take one or two already shot blasted parts.
- Degrease them with some solvent (acetone, MEK, or anything like that).
- Pickle them with the process you already are using for every part.
- Inspect them for black spots.

If the spots disappear, you have grease or oil in the pores of the material, I think you need some degreasing agent between shot peening and pickling... IF you NEED to do acid pickling (if you don't, don't pickle!)

If the spots don't disappear, grease is not the problem. Maybe, as Ted said, you have some carbon deposition in the surface (laminar or nodular graphite) and acid is making them appear, but they would be very very small, so I think the most possible cause is grease in the surface.

Sorry for repeating myself, but: If you don't need to do acid pickle, don't do it. Shot blasting does a very good job cleaning the surface, and pickling activates the surface so rust appears very fast.

Regards, and hope you can solve this issue!

Daniel Montañés
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina



Q. Hi again Ted.

Appreciate your support so far. However I would need to clarify that the casting that we currently go through the pickling process is a stainless steel casting.

I will discuss with my team to see whether we can do a test using the method as per described.

Hi Daniel,

Appreciated your support, we previously did try to use some solvent (methanol [affil links], Acetone, Sodium Hydroxide) to clean the surface. However the result still same. In such case is it mean that it could be a Heat Treatment/ Melting problem which had cause related issue?

The spot that appear are some in black and some is in brown color (rust/oxide color).

Thank you and I hope above information would sufficient for your further advice.

James Chua [returning]
- Seremban, Malaysia
May 6, 2017


A. Hello again James!

Please tell us which kind of stainless steel (AISI grade, or something like that) is the one with problems. And if you have the same problem with another steel parts.

How is the process made? Pickling, rinsed and dried? Or is another process made after the pickling?

Hope we can solve this!

Regards,

Daniel Montañés
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina



Q. Hi Daniel,

Thank you for your kind assist.

The stainless steel that having the black dot or rust mark problem is SUS304. Sorry to said that currently we only have this material that having such problem as only this material required to go through the pickling process.

Currently our process is as below:
1) Steel Ball Shot Blasting
2) Rinsed with water to remove dust before pickling
3) Acid Pickling (black dot /rust mark appear after completed)
4) Rinsed again with water to remove the remaining acid
5) Ready to send machining (if surface free from black dot / rust mark)

Kindly advice accordingly.

Appreciate your support and assist.

Thank you.

Best regards,

James Chua [returning]
- Seremban, Malaysia


A. Hi James,

When you say Acid Pickling, which formulation do you use? Acid pickling is, for most cases in carbon steel, just hydrochloric acid in water. But for SUS304, you must use other formulations, more aggressive and oxidizing than hydrochloric.

And, can you take a photograph and show the black spots?

Thank you! Regards,

Daniel Montañés
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina


A. James,
Steel shot blasting is bad for stainless. Use stainless shot or non-ferrous media like glass beads.

Daniel Montañés is right about not using hydrochloric, that is very bad for stainless. Stainless pickling is generally a nitric/hydrofluoric mix.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner



Q. Hi Daniel,

Yes indeed. We currently is using a mixture of 7% hydrofluoric acid and 20% Nitric acid in water.

I will provide the related picture for more clearer picture the defect type.

12028-2b   12028-2a   12028-2c  

Hi Ray,

Thank you for your advice. We do understand that steel shot blasting is not recommended for stainless however we been running this casting for more than 1 year and this situation only happened recently which we are struggling for the reason that cause it. But we will also moving toward your suggestion to prevent other possible causes.

Thank you.

Best regards,

James Chua [returning]
- Seremban, Malaysia


A. Hi James! Long time no see! I was in a trip with almost no time to check finishing.com Q&As as usual :P

I suppose you've read ASTM A380 [affil link] thoroughly, if not, I would.

I can relate some of this issues, and I would look for:

- Depleted acid bath (iron concentration in pickling bath?)
- The first image looks like smut, if it can't be removed by a pickling bath, it can be removed by hot alkaline potassium permanganate [on eBay or Amazon], it is risky and adds a step, but works wonderfully with smut.
- See if you have free iron in a part you have already rinsed before and after pickling (ferrocyanide or copper sulphate [on eBay or Amazon]method).

So, I'm sure you are squeezing your brains to solve this, I just hope I can help you from here!

Regards,

Daniel Montañés
TEL - N FERRARIS - Cañuelas, Buenos Aires, Argentina




Excessive amount of caustic to treat effluent from pickling plant

Q. I need economical solution other than caustic to neutralize or handle effluent from pickling bath containing HCl and other impurities.

Do I need to use pickling inhibitor if we have acid regeneration plant.

waqar

waqar haider
- karach/Pakistan
March 6, 2017

Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)




A. Hi wagar. There are more economical reagents to neutralize HCl, including lime or magnesium hydroxide; both are also safer than caustic, but each has limitations which must be worked around.

There are also ways to extend the life of the HCl bath, including better inhibitors (so less iron is consumed), and "acid extenders" (which precipitate the iron so the bath does not need to be dumped).

Regards,

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



Q. Thank you for the quick response. We are using pickling inhibitor from Rodine. Do I continue to need inhibitor if I go for acid life extenders?

waqar haider
chemical synergies - Karachi, Pakistan


A. Hi Wagar. Sorry, although I would expect that the Rodine continues to provide useful inhibition, so acid isn't wasted on raw steel, I don't really know.

In as much as both the Rodine and the acid life extender are secret proprietaries, it may be hard for anyone but the supplier to offer answers about their compatibility and symbiotic effects. I'd suggest that you ask the manufacturer of the acid extender. Good luck.

Regards,

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


A. There are several acid purification technology that can reduce the amount of caustic needed by 75-90%. You may want to investigate diffusion dialysis, acid retardation, and evaporation as a solution to this problem.

Lyle Kirman
Consultant - Cleveland Heights




Top surface of part stays rusty in pickle tank

Q. Hi,

We are having issues with one of our pickling solutions; It consists of HCl at 15% w/v. Iron is at 85 g/L and zinc at approx. 25 g/L.

When we try to pickle steel in this tank, the rust comes off on the sides and bottom of beams, but the top surface of the beams remains rusty (according to our operators)

This is the strongest and cleanest tank in the plant, and yet they say the other tanks work much better. I don't understand how that could happen.. What should I test my solution for? acid strength, iron and zinc concentrations seem to be good, and these are the only parameters we test for at our plant. Our operator has been working here for 30 years and he said this has never happened before.

Anna Terra
galvanising plant - Sydney, NSW, Australia
August 28, 2017


A. Hi Anna

Before asking for outside help you should always visit the tank and view the problem for yourself.
Even experienced operators can give a misleading description of a problem and you may spot some other factor that he did not think important.

For example...

Are you sure that the tank is thoroughly stirred before taking your sample for analysis? Witness it done or do it yourself.

geoff smith
Geoff Smith
Hampshire, England




Q. I've been selling pickle dry steel to a number of customers for several years without incident. I've advised all the pit falls to customers about using this material, which is mostly susceptibility to rust. Recently though we received a claim for this very thing. I'll talk thru it with them but I was hoping I can some help from you about the actual reasons why this is so susceptible to rust: time, surface, etc... Can you advise any literature or offer some insight?

Paul martin
metals - granite city, illinois
October 3, 2017




Q. I am an intern at a local steel company (from bioengineering) I have read this entire post several times, it's fascinating, thank you all for your wisdom.

I am trying to predict variables in coil pickling (% HCl, temp, time, speed, etc).

Does anyone have any good references? Is there a Bible of Pickling somewhere?

Thanks,

Shauna

Shauna Kocen
- South Bend Indiana USA
November 5, 2018


A. Thanks for the kind appraisal, Shauna. I don't know of such a bible although another reader might suggest one. But I will mention 4 points which I think people should not miss for a general understanding of the pickling of steel ...

1. In steel mills mechanical "scale breakers" are used before pickling to reduce the amount of scale/rust which must be dissolved in the acid and the time required. I've never seen such a device in a plating shop, but sand blasting is sometimes used for mechanical removal of rust.
2. Using inhibitors rather than straight HCl is vital. We want the acid to attack rust, but we don't want to waste it dissolving steel. I'm not a pickling chemist, but I understand that the principle is that these organic materials bind to bare steel surfaces helping shield them from acid attack.
3. There are products called "acid extenders" which can precipitate the iron or other metal out of the solution, reputedly greatly extending the life of the pickling solution.
4. The Kleingarn chart/principle which reveals that sometimes even just adding water can speed up pickling or extend the bath's life as it becomes saturated with metal. Barlow R. Campano has been generous enough to supply an excellent on-line article about it.

Happy studies, and thanks again.

Regards,

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




Q. Hi I would like to know what causes high iron content in hydrochloric acid bath used for pickling. There are 2 production lines and the one bath's iron content is low while the other bath's iron content is high.

Modibedi Mabotha
CWI - VANDEBIJLPARK South Africa
July 17, 2019


A. Hi Modibedi. The short answer is that iron readily dissolves in HCl, so you should expect a pretty quick buildup of iron. But if two baths have been operating for the same amount of time and the same amount of production, and one has a lot more iron than the other, its inhibitors or acid extenders are apparently not working as well.

If you're using lined steel tanks, maybe there's damage to the lining?

Regards,

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




Q. Hi there, I am new in push-pull pickling. And we using 4 rinsing tanks and what condition should be the water in each tank for treating the pickling coil? All finished product getting rusty after 3 or 4 days.

John patrick
November 20, 2019
- Bangkok thailand


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