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Corrosion resistance of SS316 in paper making

 

Recently, I was told that SS316 material was unable to withstand the corrosiveness of Aluminium Sulphate (pH at 1.8 to 2.0) in Paper making industry. I'm just wondering if such statement is true ? Another question is how would Kynar material compare to PFA when dealing with corrosive chemicals ?

Eng Yeow Ooi
- Banting, Selangor, Malaysia

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At that pH you basically have a moderately strong sulfuric acid solution. SS316 will stand up to that strength of sulfuric for a long time IF the temperature is 75F or below. It will pit 316 as the temperature goes up. At 80 it will last 1 -3 months. at 90, you would measure it in days.

Add a little copper or iron chloride and it will pit even faster. Add pressure or abrasion and it will destroy still faster.

Most plastics have high acid resistance, but have other weaknesses. Till you say what the use is and all of the conditions that it is exposed to, no one can help much.

James Watts
- Navarre, Florida
 

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Hi Eng!

Re your question, you really didn't advise just WHAT you were thinking of using PFA for. Personally, as a fabricator, I never, ever came across PFA as a useable material.

Compared to Kynar, ie. PVDF, it is a fluorocarbon and has excellent high temperature and physical strength characteristics, i.e., somewhat similar to teflon.

But I don't think that it is a material that is available in the form of piping, sheets (i.e., thick enough to be able to weld) and would doubt that it is truly weldable..

Kynar, on the other hand, is superb in acids and pretty good in alkalies as long as you are not in the high pH range. It is available in sheets, in piping, as valves and it is easily WELDABLE and has a max. operating temp. by memory of 140 °C. It would probably cost far less, too.

Hence it should be far superior to 3l6 stainless, subject to pressure/temperature restraints.

Hope this helps. Cheers!

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