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In our delayed coker unit, we have observed severe corrosion in Stripper Reboiler (Tubes were found heavily corroded) which is leaving heating media as Debutanizer bottom. During its 20 Years of life we have never observed corrosion in these reboilers.

What are the possible causes for this? For preventing cyanide corrosion in Gas Concentration unit we are adding Ammonium Sulphate however we have never observed cyanide level greater than 0.1 ppm in sour water anywhere in plant. Is there any chances that this Ammonium Sulphate is causing this corrosion as there is no cyanide present in the system.
29/08/2019 A: James Chacko, Suez Water Technologies & Solutions, james.chacko@suez.com
It is due to a cocktail of Cyanides, Organic acids(Carboxylates),Ammonium Bisulfides, Carbonates and other strong and weak acids.

Traditionally Ammonium PolySulphide is the chemical used as a scavenger of Cyanides. But no one has made on-line detection nor devised stoichiometric dosing of APS. Due to that it creates more problems similar to what you have mentioned. In your case, what is assumed is scavenger use without having any idea of Cyanides. Actually Cyanides are not that easy to detect and measure, as they get converted to thiocyanides

You mentioned Ammonium Sulphate, but I assume here that it is Ammonium Poly Sulphide(APS)

As a solution, I would recommend a more sophisticated way of managing this corrosion through a high persistent, super active filmer, capable of preventing Cyanide attacks. This is available with Suez Water Technologies Company. Dosage is not for scavenging but for firm persistent film formation and partially converting Cyanides to harmless thiocyanates