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sulfuric acid storage tank - 99%

2007

Hi,
I am Vijay,working water treatment plant, we are proposed to go for an sulfuric acid dosage system for the correction of the pH. The dosage of the acid will be for a period of four months remaining days it will be ideal.
We are suggested to go for the MS tank with CPVC fitting for the dosing system. Whether MS tank will withstand without corrosion during remaining eight months?

VIJAYAKUMAR
TEAM LEADER - ERODE, TAMILNADU, India

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2007

Hi Vija !

Is your sulfuric really l00% ? I used to supply sulfuric tanks for (car) batteries which used, what I thought, was commercial 94% sulfuric. They would dilute it to around 35%.

Those tanks were made from PVC using the dual laminate approach ... ditto for the Sch. 80 piping. Never CPVC.

sulfuric acid in the higher concentrations has a tendency to absorb moisture and become diluted which, for metals, is very corrosive.

Mild steel should be OK for the tank UNDER IDEAL CIRCUMSTANCES ... but there was a battery plant in Toronto using a mild steel tank on the roof but some moisture got in the line and the piping, mild steel, failed with catastrophic problems on the roof where the fire brigade dowsed the acid with alkali to neutralize it ... but that caused mega heat and the roof failed.

The PVC system worked extremely well ... by memory, the acid concentration was 94%. Mega large battery plants in the U.S.A. opted for PVC, ie. Delco Remy and in Canada it was the G.M. plant in Oshawa.

Re the piping, any connections should be back welded after min. 24 hours !

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

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2007

Is the sulfuric acid 99 wt% H2SO4?

For 99 wt% H2SO4, the corrosion rate of mild steel is about 0.02 inch/year at 80 °F, or 0.03 inch/year at 100 °F. Minimum corrosion is at about 96.5%. See corrosion table at http://www.resistoflex.com/sulfuric_graphs.htm#7
The steel should be a suitable grade, e.g., ASTM A131 Gr. B or ASTM A516 Gr. 70. See http://www.sulfuric-acid.com/techmanual/Materials/materials_storagetanks.htm

The tank should be within a containment area capable of holding 110% of the tank volume (a legal requirement in many countries). The tank should be vented to an acid fume scrubber. Blanketing the acid with dry nitrogen gas will minimize absorption of water from air.

Suitable plastics for this concentration are high-quality grades of PTFE (e.g., Teflon®) and Viton.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.