I have a question about the low car

[581127]

I have a question about the low carbon steel vessel, 16mm wall thickness in which there is a peddler. The vessel was heated by burning oil. The medium is caustic soda with some sodium sulfite, temperature is 330-350¡æ, normal pressure.
The vessel was badly corroded locally using for about 30 days. After replacing, nearly the same place on new vessel was corroded again.
My question is:
1.Why did corrosion occur locally? Is it related with pudding? How can I prevent the corrosion?
2.What is the corrosion mechanism?
3.Who can tell me where I can find the relative information?

Help me please

 

[Metalguy]

I can't decipher your temp., but caustic soda (NaOH) at ~25% boiling doesn't seem to corrode carbon steel. What % are you using, and where is the pitting/local corr. occuring? Also, what % Na sulfite, what is a "peddler", and what do you mean by "pudding"?

 

[581127]

thank you Metalguy
I have some difficulies to express in english,let me try it again
the vessel with peddler:maybe I should say agitated vessel.dia.of the vessel is 2000mm.rotate speed of agitator is 50rpm. pudding is wrong, here shoud be agitating. I mean if the corrosion is related with agitating?
NaOH concentration is 92%.