Hello Omar J. Yepez, I agree with your assumption that oxygen corrosion is one of the severe corrosion modes. This is due to the good activity of oxygen with other materials. The hydrogen and chlorine ions of the solutions are most pronounced. The presence of the two elements leads to decomposition of the oxide coatings. This also reduces the protective properties of the materials. The use of inhibitors reduces the rate of decomposition of the oxide coatings and increases their durability. It is not to be believed that corrosion is sleeping, it is only delayed. With respect Emil Yankov

Removing oxygen from the system( if possible) by mechanical or chemical means should be the first step. Though in the field we experience several places and occasions of oxygen re-entry in traces. So continuous chemical inhibitors injection can be of use in dynamic( flowing )systems. However the storage tanks used for make-up always found with traces of oxygen. Similar is the case of seawater treatment systems and pipelines. Dissolved oxygen is rapidly consumed to form iron and other oxides in the form of sludge.

Dear Omer

Yes I think so, when the inhibitors anchors on the anodic sites rather than on the cathodic sites leads to minimize the supplying of electrons to the cathodic sites and in this way you control oxygen corrosion.

Best regards

Dear Mohammed, How can we prove that?

Dear Dubravka, now imagine this kind of damage inside a pipeline!

I believe using Tafel plots might help identifying the nature/mechanism of the inhibitors. Phosphate esters might have a dual function as cathodic and anodic inhibitor ( chemisorption on anodic sites and precipitation or oxyhydroxides modification by creating a insoluble phosphate complex on cathodic sites 0

Dear Wadah, I followed the formation of the phosphate ester film with electrochemical Impedance. I saw a high fluctuation in the current before the film settled. This did not occurred in the case of imidazoline inhibitors. I interpreted this fluctuation as the difficulty of the phosphate ester inhibitor to anchor on the surface. Probably on the anodic sites. This is because iron(II) is going out from the surface. It gets cough by the phosphate functionality and does not anchor. In the case on the imidazoline the surface is not being destroyed and the anchoring of the inhibitor is easier. Does this make sense?

Dear Omer

Yes most probably you are right .. I can suggest several methods to study the film formed

1- Run FTIR-ATR for both a blank coupon and a treated coupon with the phosphate ester, compare it with the FTIR of the phosphate ester and locate where the phosphate ester adsorb. SEM/EDX might give you similar results. This probably will show you whether you have simple adsorption, or a complete new complex formed on the surface. You may do it at different concentrations and see the coverage.

2-Try to study the same system at different temperatures. Imidazoline usually exhibit a chemisorption so temperature has lesser effect on adsorption/protection as compared with an inhibitor that exhibit physisorption or weaker chemisorption. Also you can plot concentration vs protection for the inhibitor at different temperatures and see the development of protection. You may go for more complicated analysis by calculating Gibbs energy for adsorption and determine for sure what type of adsorption you have. The purpose of this study is to see the energy required for adsorption and whether your inhibitor can anchor to the surface or just adsorb due to “electrical” attraction

3- Try studying compatibility with the brine used, may be phosphate esters have limited solubility as compared with salted imidazolines. Try adding increasing concentrations of Fe2+ to the system and measure turbidity at different temperatures and iron counts. Use 500 or 1000 ppm of the PE inhibitor. You can also salt the phosphate esters with different amines ( MEA, DEA, TEA) and see what happens . Amines usually help anchoring/ precipitation and thus will increase protection at cathodic sites

I forgot to say that, unlike in acid or CO2 corrosion, in Oxygen-rich environment you might have a complex system, where ferrous oxide may play a cathode for iron and an anode for ferric oxides, thus the adsorption process is complicated and you might have several mechanism that occur at the same time

Dear Omer

Thank you for your feedback on may above answer. The effects of inhibitors on corrosion processes are :

Displacement of the corrosion potential in the positive direction indicate mainly retardation of the anodic process (anodic control), whereas displacement in the negative direction indicates mainly retardation of the cathodic process(cathodic control).

Small change in the corrosion potential suggests that both anodic and cathodic processes retarded.

Best regards

Reference: LL. SHREIR, corrosion , 2nd ed. , p- 18-38(1979).

Dear Dr. Mohammed

This is clearly illustrated in Tafel Plot when the slop of the cathodic or anodic branch changes between blank and inhibited solution

I dont think that way. Unless the bacteria involved in such reaction are completely eliminated and then such reactions has to be studied. Hopefully this is the case when you experienced the oxygen corrosion being the hardest corrosion regime .

Thanks