Saturday, November 1, 2008

Why CO2 with present of water is corrosive ?

Carbon dioxide (chemical formula: CO2 ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and present in oil and gas fluid. CO2 by itself is not corrosive, however, with the present of free water (H2O), it becomes corrosive and poses a thread to many oil and gas facilities.

CO2 with present of free water would lead to generation of Carbonic acid (H2CO3).

CO2 + H2O ==> H2CO3 ==> H+ + HCO32-

When Carbonic Acid contact with steel (Fe), reaction occur.

2Fe + H2CO3 ==> Fe2CO3 + H2

With minimum level of Oxygen would aggregate the corrosion :
Corrosion without Acid Carbonic :

4Fe + 3O2 + 6H2O ==> 4Fe(OH)3

and Corrosion with Acid Carbonic :

Fe + 2H2CO3 ==> Fe(HCO3)2 + H2

2Fe(HCO3)2 + 1/2 O2 ==> Fe2O3 + 4CO2 + 2H2O

Carbonic acid is weak acid would reduce the pH of fluid and this further aggregate the corrosion.

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