Sulphuric acid vapours and glavanized steel

[davidet68]

I need to feed Sulphuric acid @98% to neutralize a discharge water in a basin. This concrete basin will be covered with a Carbon steel hot dip galvanized structure. I would like to know if the acid vapours produced inside the basin can cause corrsion problems to the galvanized cover and in this case which kind of painting can be suitable to protect the galvanized steel.

Thanking you in advance,

Davide

 

[ash9144]

You will have problems with 98% and weak acid formation as the acid blends with water. Your best bet would be pvc. Galvanized shouldn't be used in any sulfuric service. There aren't any paints that do well at all in sulfuric either.

 

[strider6]

You said that you add H2SO4 to neutralize the water, so i think that your water inside the basin will not be acidic, but at pH around 7.
In this case i don't see the possibility to have acid vapours and following corrosion of the galvanized steels.
regards

Vitt

http://www.corrosionist.com

 

[ash9144]

If the pipe extends into the water there will be an interface where the acid and water initially blend at the water surface. This will produce weak acid which would cut the pipe even with the waters surface in a matter of a few hours. At least that is what happened at the sulfuric acid plant I worked at.

If the pipe doesn't extend into the water there will be splashing and weak acid formation in the area which will destroy the pipe but at a slower rate.

 

[strider6]

Maybe the materials you've selected for the pipe was not suitable for the service. Was it a carbon steel?
Vitt

http://www.corrosionist.com

 

[davidet68]

The main pipe is carbon steel with 6 mm of Corrosion allowance, but at the inlet of the basin the pipe will be PTFE to avoid corrosion. The end of the pipe is deep about 500 mm in the water to avoid splashing and weak acid formation.

 

[ApC2Kp]

davidet68,

The PTFE acid injection pipe sounds adequate for good mixing into the water stream. An open-end PTFE dip pipe is probably better than a sparger with spray hole pattern. When there is zero acid flow, water will back up inside the dip pipe. When acid flow starts up, there could be acid - water reaction inside the dip pipe. The acid - water reaction could be violent enough to blow off the end of a sparger.

Acid plants have their structural steel either galvanized, or painted with two coat epoxy primer + paint for corrosion control. A few plants use fiberglass grating. The problem with epoxy paints can be the difficulty of adhesion for any maintenance touchup. Some prefer epoxy primer with a polyurethane top coat which can be maintained easier. Corrosion is slowed, but re-painting is required depending on acid concentration, temperature, and splash frequency. You might consider a PVC splash shield over the area downstream of the acid injector. It could be interesting to try something like the spray-on truck bed liners on your galvanized basin covers.