Metal finishing Q&As since 1989

-----

Chock of the ball valves after attack by 96% sulfuric acid

Dear all,
We have in use since 1 year 316L stainless steel pipes, fittings and ball valves (with TEFLON seals) for storage, transportation and filling of sulfuric acid 96.3%. We use it as a pickling agent for copper and brass strips after rolling. The problem is the valves: they are blocked very often let say after 1 month working time or even less, due to formation of solid bluish crystal substance between ball of the valve and the body.

What do you think is the reason - is the corrosion reaction after decrease in the acid concentration (moisture suction from the air). Generally the problem is observed on the valves which are staying without acid for a longer time. Should we be looking for another type of valve instead of ball valve or different material such as PVC or CPVC?
What do you propose for avoiding suction of moisture from the air? In case of that we have a tank with a pump which discharges given quantity from it, it's necessary to have a hole in the top of the tank for equalization of the pressure in the system.
The temperature of the acid is ambient -5 to +30.

Aleksandar Stefnov
- Sofia, Bulgaria
2006

---

2006

Hi Alexsandar

I think that you've hit the ball on the head with your surmise of the moisture in the air.

sulfuric in the upper concentrations absorbs water/moisture like crazy which leads to corrosion.

Why don't you try out a good PVC ball valve. I'm prejudiced and would opt for U.S. ones called Plast-0-matic but any 'good' ones with a teflon or Viton O-ring seats (NEVER epdm) should be OK.

You at least gave the concentration AND the temperature, which many forget to do. Gracias, Danke, Merci, Thanks !

PVC according to the charts is OK to 94% sulfuric at R.T., but when you get moisture, the concentration drops and I think that they should last till the cows come home.

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

---

I suggest metal seated ball valves - excellent reliability.
The metal seats will brake away the deposit on the balls while the valve is operated and will avoid valve blocking.

Kind regards,
L. Kiss

Ludovic Kiss
Germany
November 20, 2008