Summary for hf tank lining materials Discussion
HF tank lining materials are the focus of this thread, and the consensus is that stainless steel is not the right choice for a 4% hydrofluoric acid / 12% nitric acid pickling bath at 60 °C. Freeman Newton suggested asking a manufacturer of flexible PVC linings, saying that sounded suitable. James Watts reported success with a very heavy vinyl liner in a heated nitric/HF tank, but warned it would not last as long at 60 °C, which is near the upper limit for most vinyl liners; he suggested a CPVC tank with fiberglass coating for strength, though at higher cost. Skip Schaefer recommended a polypropylene outer tank with a 1/4" PVC liner, noting the liner would likely need yearly replacement and that heating should be done with hot water through a Teflon coil. Jono Choi said a PFA Teflon tank would offer the best longevity for the money. In the merged electropolish discussion, Ted Mooney and James Watts favored a drop-in flexible liner over coatings when cracks are present.
Q. I’ve been recommended a pickling mixture of 4% hydrofluoric acid, 12% nitric acid to remove oxide scale at 60 °C.
What materials can I use ?
I guess glass is out due to the HF. Also not all plastics are compatible with nitric acid.
Is stainless steel OK?
Thanks
Tony
Tony Fulford
– Reading, UK
2000
A. I’d suggest talking to a manufacturer of flexible PVC linings (either glued in place or drop-in style) about this application–it sounds fine to me.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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A. Hi Tony,
I have some doubts that stainless will survive your ‘mix’ although nitric protects stainless as you know. Why don’t you check with the corrosion charts of any local s.s. supplier?
PVC by itself is no good due to temperature deflection (but only perhaps as a lining) but I don’t like the idea of the plasticized PVC, which linings are made of, in conjunction with nitrics, especially fairly hot ones as the plasticizer will get leached out.
You should be OK a glass reinforced PVC, a so-called dual laminate. Then there’s CPVC, PVDF and the weldable fluorocarbons, which cost a mint. All will take that mix.
Cheers!
Freeman Newton [deceased]
R.I.P. old friend (It is our sad duty to
advise that Freeman passed away 4/21/12)
A. We used a very heavy (about 1/4″) vinyl liner in a heated nitric HF tank and it lasted about 10 years. It would not last as long at 60 °C which is near the upper limit of most vinyl liners. You are probably looking at a CPVC tank with a fiberglass coating for strength. They tend to be dear when it comes to price.
James Watts
– Navarre, Florida
A. Tony, Your best bet is to use a polypro outer tank with a 1/4″ PVC liner. The liner will need to be replaced at least once per year. For heating, use Hot water through a teflon coil. Keep the pressure though the coil below 20 pounds per square inch.
George Fischer (GF) manufacturers the best line of teflon coils. For teflon heaters less than 12000 watts call Lufran. Sincerely,
Skip Schaefer
– Pomona,California
A. Tony,
Unless you enjoy replacing your tank on an annual basis, I suggest using a PFA teflon tank. If you are using 4% HF, 12% nitric acid, a PFA tank will give you the best longevity for your money.
Jono Choi
– Arcadia, California, USA
Multiple threads merged: please forgive chronology errors and repetition 🙂
Coating for Electropolish Containment Tank
Q. I am looking for a material that can be applied to our spill containment tank around our electropolish tanks. Our containment tank developed some cracks when it was moved. I need a coating that will stand up to the electropolish solution and something that will seal cracks in the tank to allow it to be washed out.
Brad Wilson
– Simi Valley, California , USA
2003
A. I don’t think I’d trust anything but a drop-in flexible liner considering the cracks and the poor adhesion to an old surface that I’d expect. What is the containment tank made of? Polypro? FRP?
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
 | A. Too many unsaid variables. Concentration of each component of your EP solution. If there are proprietary components, you better ask the manufacturer of what you can use and more specifically, what you should not use. Next, what is the ambient temp under the tank. Drip spills or splashes? Initial gut reaction is pull the tanks out, use a chopper fiberglass unit with the appropriate formulation, smooth out, apply a very tight weave veil coat and at least two coats of gel coat on top of that. Put the tanks back in. James Watts A. Brad, You didn’t spec out what that thar tank is made of … and lacking info, how in the heck do you expect anyone to try to help you? As Ted suggests, a drop-in liner should work OK … The normal liners being plasticized PVC. Then if that tank is just for overflow purposes, instead of a heavy (& expensive liner) go to a swimming pool Company and get a liner from them … the swimming pool liners do come in a variety of thicknesses but nothing as heavy as an industrial 1/8″ or 3/l6″ thick PVC liner.
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Multiple threads merged: please forgive chronology errors and repetition 🙂
Liner material for nitric acid tanks
Q. We have to use an existing Mild steel tank to supply nitric acid (60% concentration). I would like to know the type of liner material to be provided in the tank. Size of the tanks is 3 m X 3 m X 4 m. Also please note that the lining is to be preferably done at a construction site.
Thanks,
Ramesh Babu
Engineering & Consultancy – Bangalore, Karnataka, India
2004
A. Nitric acid tanks would ideally be made of 316L stainless steel, but a PVC drop-in liner will work if you don’t overheat it when adding acid.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
adv.
