Summary for titanium heaters in chromic acid Discussion
Titanium heaters in chromic acid are failing quickly, with the questioner reporting only 4–5 months of life at 70 °C in a chromic acid bath containing free iron radicals. Gene Packman said that, based on chemical resistance charts and experience, the only electric heater shells that reliably withstand chromic acid/sulphate plating solutions are quartz or PTFE (Teflon). Trevor Crichton suggested PVDF as another acid-resistant option, noting it can handle up to about 140 °C but has drawbacks in high pH and slower heat transfer; he also mentioned a solid PVDF unit he sold to a chrome customer that was still in service. Salim recommended a lead-bonded heater for chrome solution. James Watts added that the short life likely indicates the heaters are being run at full rating, and advised derating them for longer life, or double-derating for even better life.
Q. We use titanium sheathed heaters in 122-15% chromic acid containing free iron radicals. Temperature maintained is 70 °C.
We experience rapid corrosion of the wetted titanium tubes. Life experienced is 4-5 months when continuously immersed.
Kindly suggest ways to improve life.
regards
MANOJ M DESAI
HEATER MANUFACTURER – MUMBAI, INDIA
2005
A. According to the chemical resistance charts and prior experience the only electric heater shells that stand up to chromic acid/sulphate plating solutions are those with an outer shell of Quartz or Teflon (PTFE).
Gene Packman
process supplier – Great Neck, New York
2005
A. Hi Manoj
Wouldn’t PVDF be a better material? Superb in acids. OK for max 140 °C
… but doesn’t like high pH.
Freeman Newton [deceased] (It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).
2005
As we all know, chromic acid is disgusting stuff that creeps everywhere and attacks just about everything. Gene and Freeman are right in suggesting a polymeric or ceramic coating to protect the heaters – pH will not be an issue because chromic acid has such a low pH that is almost falls off the scale!
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005
Use lead bonded heater for chrome solution.
Salim
– Saudi Arabia
2005
First of two simultaneous responses —
From the life of your Ti heaters, I will guess that you are using full rated heat in your heaters. For longer life, use derated heaters and for even longer life, use double derated heaters.
James Watts
– Navarre, Florida
2005
Second of two simultaneous responses — 2005
Trev.
I didn’t infer a ‘coated’ PVDF heat exchanger … but a solid PVDF unit.
Disadvantages? Heat transfer is slower than metals. Advantages….ENORMOUS ….I sold one to a chrome customer who, as far as I know, is still using it.
PVDF costs an arm and a leg. Mind you, Salim’s suggestion of lead sounds very good … and probably less expensive than PVDF.
Freeman Newton [deceased] (It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).