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"Tank material for chrome plating and chromic acid"



Current question:

June 30, 2021

Q. We do hard chroming in our shop and we noticed a small crack in our tank. We are trying to get a new tank but we don't know what direction to take.

Manuel Perez
Consumables/In-direct supervisor - Englewood Colorado
^

  ^- Privately respond to this RFQ -^


July 2021

A. Hi Manuel. Although there are alternative possibilities as discussed on this page, Koroseal (PVC) lined steel tanks are still a fine answer: they are economical, there will be no bad surprises, and steel is very strong in the event of any sort of material handling accident with heavy rolls or whatever.

What is your current tank made of which has developed a small crack?

Luck & Regards,

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

simultaneous
July 8, 2021

A. Hi Manuel,
I would go for a stainless steel tank with Koroseal liner. There are options to make a Koroseal liner with a Teflon-based upper part (skirt). It is a recommended improvement as a liquid level is probably the most aggressive area of the bath.
Good luck.

Leon Gusak
- Winnipeg, Canada
^


July 9, 2021

A. A rigid Kynar (PVDF) Copolymer as a box liner inside of a steel tank can be a "forever-tank" option for hard chrome plating when fabricated by a reputable supplier who will guarantee no weld failures. It is relatively expensive, but it pays in the long term since it would not require periodic replacement. A steel tank with a bonded Koroseal liner with a teflon skirt at the solution level is the next best thing. Replaceable bag liners are still very commonly used because of the lower up-front cost, but they have a relatively short useful life.

Jon Barrows
Jon Barrows, MSF, EHSSC
Independence, Missouri
^


July 2021

A. A final option, because it may have occurred to you, would be a self-supporting tank made of rigid Kynar. I designed a few for a chromate manufacturing facility but they cost more than 10X what similarly sized rigid polypropylene tanks cost. And even ignoring the cost I don't think they would be appropriate for a hard chrome plating line where mechanical damage is a possibility :-)

Both Leon's and John's suggestions sound better to me.

Luck & Regards,

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




Flexible PVC (Koroseal) and lead lined tanks have long been the standard, but Kynar and titanium are additional possibilities. Read on...

Closely related historical postings, oldest first:

2006

Q. What would be the best tank material for 16% chromic acid at 200 °F? I am planning to line a 316SS tank. It looks like even Kynar (PVDF) has trouble with chromic acid above 180. I could go with Teflon, but it is extremely expensive. One tank manufacturer has suggested having the tank coated in Halar. This too is pricey, but less than teflon. It does appear that this would do the trick, but I am curious if anyone else has a better idea.

Jon Barrows
Jon Barrows, MSF, EHSSC
Independence, Missouri
^


2006

A. Hi Jon,

You've seemed to have done your research but why a liner?

Why not make the tank from a good dual laminate material such as CPVC/FRP ... (going by memory, PVC/FRP is only good for 180 °F, and therefore perhaps not suitable).

You may not want to buy this from Canada but for a first class opinion, go to DUALAM in Vancouver, their top design engineer is Enrique Ginocchio.

After all, dual laminates were INVENTED by Canada.

An afterthought ...normally these fluorocarbon liners, due to their cost, are very thin ... 0.06" thick but are available to 0.90" which allows for a far better weld ... and you must consider 'scratching and scraping' whereas the CPVC material would probably lend itself to a good dual laminate thickness of 1/4".

Heavier thicknesses are easier available but would not, I feel, be advantageous for a good dual laminate construction.

freeman newton portrait
Freeman Newton [dec]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

^


2006

thumbs up signThanks Freeman. Most people are telling me that while CPVC will take the temperature in general cases, it does not like chromic acid above 180 °F. Above that, the welds will be attacked over time. I understand that is true even of the dual laminates since the weld is still CPVC.

I am starting to learn about some newer modified versions of CPVC that may work. I'll let you know what I come up with.

Jon Barrows
Jon Barrows, MSF, EHSSC
Independence, Missouri
^


2006

A. Hi Jon,

Your comment about CPVC not being suitable, weld-wise, above 180 °F may well be very true .

Having run, in Ye Olden Days, weld tests on 1/2" PVC, it was interesting to note that our highly trained thermoplastic welders hit all well over 85%, one guy hitting the incredible figure of 100%... but a union, who wanted in on the game, said that WE CAN WELD and why use a non-union shop, only hit, guess... 30%! I am an incredible welder and hit 27% hence maybe I should be unionized ?

Therefore maybe the weld integrity is highly important, certainly is with 3l6L s.s. in a marine environment! The weld rod MUST be very compatible with the original material, i.e., easy to use.

Re your comment about other dual laminates using CPVC weld rod ... that ain't true. The only two interweldable plastics are uPVC and Acrylic.

freeman newton portrait
Freeman Newton [dec]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

^


2006

A. How about a lead liner? Lead is used to contain plastic etching solutions (normally mixtures of sulfuric and chromic acids at high temp) and it's not so expensive.

Guillermo Marrufo
Monterrey, NL, Mexico
^


2006

A. Jon,
You might want to look into a solid titanium tank without a liner. Titanium is used for Chrome Plating tanks in the rotogravure printing industry. Their operating temps are much lower than 130-140 °F, but the concentrations are similar. Many have been in service for years without any pitting or weldment failure problems at all. As a tank fabricator, I know 316SS Flat Sheet Prices have gone through the roof, due to high nickel demand, but I haven't priced Titanium lately. I hear there were some good prospects in East St. Louis back during Surfin...

Kyle Hankinson
- Forest City, North Carolina, USA
^



2002 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I have a client who wishes to use a titanium tank for a small to medium size hard chrome plating facility using HEEF 25N. Does anybody have any experience with titanium as a tank liner material in this solution, and what grade/alloy of titanium did you use?

Peter Robbie
- Australia
^


"Chromium Plating"
by Weiner & Walmsley
from Abe Books
or

(affil. link)
or
see our Review

April 9, 2010

A. Hi, Peter. Titanium has been used for hard chromium plating tanks as you read above, and I don't think the non-fluoride catalyst in HEEF-25 would be a problem for it. Still, we see a lot of periodic reports of titanium reacting strangely in the plating industry, perhaps due to the many different alloys.

I guess I would suggest that end users get a guarantee from their tank supplier, whereas suppliers should acquire some experience from jar-testing welded samples and building small tanks before committing to big ones :-)

Sorry that this answer probably isn't much help! But I've seen a fair number of spectacular failures of titanium (like failure of all titanium heating and cooling coils on a whole plating line) that were never satisfactorily explained, so I don't claim a full understanding of the electrochemistry in plating applications. Good luck!

Regards,

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



2004

Q. Has anyone had experience of using epoxy type coatings on chrome plating vessels at 25% concentration and 50 °C? I believe that there are coatings available but I have no idea how they perform.

Graham Hall
Hard Chrome plating - Port St Mary, Isle of Man, Great Britain
^


2004

A. Hi Graham. My vote is to let someone else try it because I don't know for sure, but strongly doubt that epoxy coatings would work. Chromic acid is nasty, highly oxidizing stuff, and I would only trust soft vinyl (Koroseal or equal, or a drop-in PVC liner), or an exotic material like PVDF (Kynar)

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


2004

Hi Graham,

A. What Ted says makes sense ... but PVDF is damned expensive and if you used a solid liner, that takes EXPERTISE ... in ye Olden Days we used to make solid PVC liners ... but the flexible PVC liners make more sense due to no worries about expansion and contraction of rigid liners.

Epoxy? Well, some people have used fibreglass liners but they don't last long and they are not homogenous like thermoplastics... and probably some of the special FRP resins might be better than epoxy such as Hetron l97. The advantage of epoxy is that it can glue itself to steel very well ... on the other hand it is expensive and not so easy to work.

If this is a short term usage, consider a swimming pool liner. Now the Koroseal people will shudder at the thought BUT those liners can be had in different thicknesses, maybe not as heavy as the 'professional' ones ... so opt for the heaviest PVC swimming pool liner you can (maybe two of them) ... and they'd cost far less.

I wish you success!

freeman newton portrait
Freeman Newton [dec]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

^



November 30, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. What should hard chrome plating tanks be made from?
How many for the complete hard chroming process?
What would be in each of them?

Abdulla Abuhadhood
Buyer (looking to start new shop) - Jeddah, Saudi Arabia
^


"Hard Chromium Plating"
by Robert K. Guffie
from Abe Books
or

(affil. link)
or
see our Review

December 1, 2011

A. Hi, Abdulla.

There are 3 different hard chroming formulations: the Sergeant (or conventional 100:1 chrome to sulfuric) bath, the fluoride catalyzed bath, and the HEEF bath. Materials of constructions could be different, depending on your choice, but the most common material is hot rolled steel with PVC lining. Freeman Newton's on-line article "Hard Chrome Plating - Materials to Consider" may be helpful to you.

The fluoride bath cannot be used for etching, so you need a separate etching bath if you go that route. You need cleaning, rinse, etch, rinse, hard chrome plating, and multiple rinse tanks. Depending on what substrates you intend to chrome plate, you may need others. But, really, the equipment is not nearly as important as chrome plating knowledge.

If you cannot retain a consultant, or experienced hard chrome plater, or tech service person from the local supplier to guide you, please see if you can get access to a copy of Guffie's book =>
It's a small book of about 180 pages so it doesn't cover everything, but it does address a lot of very important points. Good luck!

Regards,

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



Is titanium liner satisfactory for non-fluoride hard chrome plating?

March 11, 2014

Q. I am considering a titanium liner for one of our hard chrome plating tanks. We are using HEEF 25 chromic acid that is not fluoride based. How long would you expect the life expectancy of a titanium sheet liner of .078" thick to last with a daily plating load? Would there be any issues with conductivity or plating performance with the titanium having a low electrical conductivity? Does anyone have experience or feedback on titanium liners in general?

George Lesher
- Springfield, Ohio, USA
^



July 9, 2014

Q. I am wondering if this conversation is based more on the chrome solution as a whole or just the chrome component?
I am building a tank for my type 2 passivation and was told that I need to use CPVC because of compatibility concerns for the sodium dichromate. Is this the best way to go?
My current tank just failed and it looks like it has a CPVC liner.

Michael Silva
- Carson, California USA
^


July 2014

A. Hi Michael. A standard soft PVC liner like Koroseal, or a PVC drop-in liner should be satisfactory since the temperature would be under 140 °F -- although most passivation tanks are probably built of stainless steel.

Regards,

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


July 11, 2014

Q. Thanks Ted
One last question, since temperature controllers can fail and my solution would rise to the 180 °F temp of the boiler water. would there be a benefit to CPVC over stainless or visa versa? Also, what grade of stainless would be best for the type 2 passivation?

Michael Silva [returning]
- Carso, California USA
^


July 2014

A. Hi again. Sorry, I don't accept the argument that CPVC is necessary because of the possibility that the temperature controller might fail. There are all kinds of other issues and hazards if the temperature rises to that level, and I don't think it's grounds for not using the standard soft PVC liner approach.

Type 316L is the highest grade of stainless commonly used in the fabrication of plating and metal finishing tanks. I would accept a lower grade only if the supplier assures you with their relevant experience and their guarantee.

Regards,

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


July 31, 2014

A. Michael,
As an aside, if you are able to consider moving away from the hazardous chemistry involved in nitric acid passivation baths that have a tendency to destroy the equipment, much safer citric acid based alternatives are available.

For a nitric passivation bath you're probably safest with 316 as Ted suggested. A citric bath can be done in plastic tanks if desired, though.

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


August 5, 2014

A. Dear Michael. You can use PPCP (Polypropylene tank) also for better life.

Ilesh G Vyas
Gunatit Builders
supporting advertiser
Manjalpur, Vadodara, Gujarat

gunatit builders
^



November 3, 2015

Q. We're looking to add a chromate conversion process for magnesium. It calls for a dip in a 3% to 6% chromic acid bath at room temperature. This should be a fairly small tank, 2 ft X 3 ft X 1.5 ft deep. and within a process room that has a drainage trough around the edge, so a tank failure would not be catastrophic. What's the best material for the tank and rack systems for a reasonable useful life? Should I have any concerns for galvanic coupling during the 8 minutes it would be in the bath?

Thanks for your help!

-Kirby

kirby_wilkerson
Kirby Wilkerson
aerospace - Bristow, Oklahoma, USA
^


A. Hi Kirby. Nearly any typical plastic construction material (PVC, CPVC, Polypropylene, Vinyl Ester Fiberglass) should be fine. A Koroseal (PVC) lined steel tank is fine too. I believe that titanium racks should be okay, although plastisol coated racks would eliminate any possibility of galvanic activity and be more foolproof if they suit the work you're racking.

Luck & Regards,

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

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