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Acid Corrosion

 

Looking for coating for finned tubes to with stand sulfuric acid Condensed from flue gases. Tube metal temp. 60-260 oF.Acid 10-75%.

Keith Veitch
combustion & energy- Markham, Ontario, Canada

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Keith,

That's a bit of a tall order, I think .... maybe PVDF is OK which in piping form is said to be good to l40 degr. C ... then, for more $$$, you have fluorcarbon coatings like Halar or FEP teflon. You sure have a fluctuating temperature range!

I did run across a major sulfuric problem in the 0.2 to 0.8 micron range, concentration? unknown but fairly high. Temperature was around 80 °C ... emissions from a Joy scrubber where gangue 'scrap piles' were previously heated up to horrific temperatures to regain Pa and Te. Where? Inco #2 plant in Port Colborne in Ontario. During inversions the city had problems! When? l974-ish.

They used mist eliminators but all the mesh ones plugged up and were nbg so they used an inertial L.M.I.T.S design and got around 86% efficiency. Anyhow, I thought that this might interest you.

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

Keith,

What is your tube material and where is the acid going to be? If it goes thru the ID you could probably get pipes lined with Hastelloy or something similar, but if the acid is on the finned OD, then you really have a big one as the temperature and concentration is really too aggressive and the geometry a headache for most processes. I doubt there is something good enough that can be applied to OD and work. Even electroless nickel (EN)will probably fail at several weak points making the problem worst in weeks. Unfortunately, I don't think the previous letter will apply for your problem since plastics are heat insulators. So, only very sophisticated and cost prohibitive processes could claim some success and not for every substrate. Maybe a thick cyanide copper (0.002" min!) followed by thick high phosphorous EN (0.003" min.) followed by a final bake to diffuse both will do if engineering constraints allow it. Another idea would be to apply a thick CVD nickel coat (on the order of ! 40-80 mils thick).

Good luck.

Guillermo Marrufo
Monterrey, NL, Mexico
 

A rhodium (or platinum if you can afford it) plating would probably do the trick, and it is possible a thick parylene (C or N) coating might work if you used a crosslinked interlayer for adhesion. There are quite a few exotic surfaces which will isolate steel from sulfuric acid, but processing is sometimes limited to small parts. If this is a sampling device, drop us line.

Dale Woika
- Bellefonte, PA, US
 

I would try High Phoporous Electroless Nickel duplexed with a top coat of electroless nickel teflon.

Todd Osmolski
- Charlotte, North Carolina, USA