Sulphuric Acid Tank Rupture

[Milutin]

Few weeks ago we have sulfuric acid tank rupture; sulfuric acid concentration is 98wt%.
Rupture happens below outside plate heater. Plate heater is copper plate, dimension 1m x 0.5m, heating medium is low pressure steam, it is mounted on tank wall (bottom of tank) under stone wool insulation. Tank was made from carbon steel.

During inspection we discovered on tank wall, in place where was plate heater position, large quantity of rust, in all other positions tank outside wall was in good condition, with paint on place. We discovered five holes on tank wall on position below heater. Three holes seems as they ruptured from outside (shape like crater) and they were all in same level, other two holes looks as they ruptured tank wall from inside, no craters present.
What is caused rupture, galvanic corrosion or some other cause?

Regards,

Milutin

 

[Compositepro]

It certainly sounds like a clear case of galvanic corrosion from your description.

 

[kenvlach]

Plus, elevated temperature from the heater.

 

[EdStainless]

Plus, moisture trapped in insulation.

I presume that these areas had been painted to start with. Better surface prep, paint and inspection are all in order.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Milutin]

Yes it was painted in moment when heater is mounted.
My idea is to change this copper heater with carbon steel one.

Regards

 

[bimr]

What do you mean by rupture? One would think that the leak would have started with a small leak rather than a rupture.

Rupture is defined as a state of being torn or burst open

 

[Milutin]

bmir you are right, sorry for my english.
Anyway, leak rate was 2.5m3/h.

Regards,

 

[EdStainless]

Well, going with CS for the heater coils gives you one more part to keep protected. Cu should be fine you you coat your tank properly.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[MJCronin]

Milutin..

What temperature are you trying to maintain and why ?

(Having concentrated H2SO4 at elevated temperatures is asking for a corrosion problem....Is there a process reason why you must maintain this temperature ?)

Where is the tank located ? (in what country ?)

Using carbon steel for this service is only a good idea to about 125F...... as I recall

-MJC

 

[Milutin]

We are trying to maintain 86degF (30degC)in tank, that is protection from low ambient temperaturas.
Tank temperature is regulated by control valve.

Regards,

 

[ash9144]

Even if bulk tank temp was controlled at a reasonable level there would be localized hot spots at the exchanger. Most exchangers I have seen in service at elevated temperatures and sulfuric acid have been made of hastalloy.