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Suitable material to withstand hydrofluoric acid corrosion at 50 °C

We are manufacturers of heating systems. We need to heat hydrofluoric acid solution (Concentration :50-100 gm per lit.). We were looking for suitable material for the heater outer sheath. What material is best suited for such application?. If we coat a layer of Teflon on SS316 or 304 pipe, will it withstand the corrosion. What is the optimum thickness of coating required to heat hydrofluoric acid solution up to 50 °C.

K. P. Haridas Menon
Manufacturing of heating equipments - Mumbai, Maharashtra, India
2004

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Hi K.P.

Without checking (which I'd ALWAYS do when it came to the nitty-gritty), I would have thought that 3l6 s.s. might perhaps be OK by itself.

Re the plastics, you might just get away temperature-wise with CPVC, certainly any of the fluorocarbons but consider PVDF as it is OK to l40 deg. C.

There are, too, PVDF heating coils ... available for years and years.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
2004

If this is a batch operation, you can build a double wall tank made of ultra high molecular weight polyethylene (UHMW)or polypropylene and circulate hot water between both walls. If it is a continuous operation, a similar approach with a heat exchanger would be safer than a coated metal immersion heater. You should remember that HF is extremely dangerous and aggressive to all forms of life, thus the tank or heat exchanger must be isolated and protected in case of a leak. No stainless steel or exotic alloy can safely do the job, only gold and some of the platinum group metals resist HF.

Guillermo Marrufo
Monterrey, NL, Mexico
2004

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Hi again K.P.

What Guillermo suggested could, I guess be done, but only use Polypropylene as ultra high molecular Polyethylene does not lend itself to welding ... but one could use ordinary h.d.Pe instead.

If, if, if it's necessary to have an outer 'spillage' tank, then I'd only make it a few inches wider and only say 9" high so that one could see if there had been any leaks ... and use h.d. Pe.

I believe that G.F. Fischer supplies the pvdf heating coils, but I think that Titanium is resistant to HF but never, ever to HF mixed with nitric.... and there should be titanium heating coils, probably at a helluva price,too.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
2004

adv.