A-36 Plate Steel for Sulphuric Acid storage tanks

Have designed and inspected many H2SO4 tanks and never heard of not using A36 material for the shell, bootom or roof.

Steve Braune
Tank Industry Consultants

We have several, concentrated sulfuric acid storage tanks that are fabricated of rolled and welded carbon steel plate and operate at room temperature. There have been no problems with these tanks provided the sulfuric acid concentration remains at or above 93%. So, the literature you may have seen could have warned about the limited use of carbon steel for sulfuric acid storage tanks. If any moisture ingress occurs to the storage tank, this can dilute the acid and result in local corrosion.

One of the early NACE recommended practices for sulphuric acid storage tank does not recommend the following steels for use for sulphuric acid storage tanks: A285, A283, A515, A36. No reason is given.

The following grades should be considered: A516, A573, A662, A131 Gr. B, all normalized over 3/8"

The recommended ones are much tougher. Maybe that's what they were basing it on?

Steve Braune
Tank Industry Consultants

sulphuric,
Please advise me about the specific document (NACE RP xxxx).

I got the information from an early version of NACE RP0294-94 Design, Fabrication, and Inspection of Tanks for the Storage of Concentrated Sulfuric Acid and Oleum at Ambient Temperatures

Steve,

Of the concentrated sulfuric acid tank you have delt with, what is the ASTM designation you most commonly find ?

I have personally inspected a 30 year old A285 carbon steel tank ( with 0.5000 wall) that was used for storage of 93% sulfuric acid. No real corrosion on the shell after 30 years......some flow induced corrosion on one nozzle.

Sulfuric,

How does the sulfuric acid distingush between ASTM grades of carbon steel ? Either carbon steel is acceptable for the sulfuric acid at the storage temperature or it is not... How can pressure vessel quality steel make a diference ? What is your source of this knowledge....???

If the steel is produced to ASTM specification it should make no difference....

References.....not opinions ...please !!!



-MJC

MJCronin,
A283 and A36 was common for the most tanks. Have seen A516-70 to a much lesser extent. A very sophisticated acid producer in Canada had a pretty tight spec for their larger tanks (100ft+) that included tougher grades such a A516 and some of the CSA WT grades. The toughness was base on DMT issues, not acid service. Regardless of grade, always remove mill scale for this acid service.

Steve Braune
Tank Industry Consultants

just a side question, how do these A283 and A36 compare in corst C-276. we use C-276 screw for sufuric acid even low concentrations 20% at 130F screws cost like 8 bucks a peice is ther somthing cheaper

A283 and A36 are lower strength carbon steels that are suitable for concentrated H2SO4 at ambient temps. Its about lowest cost material that is used for tank constrcurtion. I suspect the C276 was chosen for tenmperature issues or due to lower concentrations.

Steve Braune
Tank Industry Consultants

RafaelBosch,
I have see sulfuric acid tanks built of carbon steel that have been in service for 15-20 years. Unfortunately I don't remember the grade of steel!

I believe A36 is not considered a killed carbon steel, whereas A516 Gr70 would be... But this probably has little bearing on sulfuric acid service. I guess what I'm saying is there are some metallurgy differences between the steel grades as well, but doubtful enough to make a difference.

I suspect the literature on storage tanks you mentioned discouraging A36 storage tanks has more to do with structural reasons than corrosion. A36 also doesn't go as low temperatures as other grades.. if MDMT were a consideration.

Whatever grade of carbon steel you go with - sulfuric is more corrosive at lower concentrations. Moisture ingression into the tank would dilute the concentration, consequently increasing the corrosion rate.

What I typically see on sulfuric tanks at cooling towers (for pH control) is atmospheric tanks with a vent dryer on the vent line, because the atmospheric tanks would breathe in during tank unloading.

I realize this is way late from your question, but hope it helps anyway.