The presence of ammonia, hydrogen sulfide and varying levels of cyanides in FCC main fractionator overhead systems means there is potential for corrosion. Corrosion mechanisms normally found are bisulfide corrosion and hydrogen-induced corrosion due to cyanides.

Bisulfide corrosion is caused by the conversion of hydrogen sulfide in high pH water to bisulfide, and the direct reaction of bisulfide with iron in the process materials. The application of Nalco Water filming inhibitors specially designed to operate in high pH environments minimizes this corrosion.

The presence of cyanide ions can accelerate bisulfide attack and promote hydrogen induced cracking mechanisms, such as:

1. Hydrogen Blistering
2. Sulfide Cracking (SSC)
3. Hydrogen-Induced Cracking (HIC)
4. Stress-Oriented Hydrogen-Induced Cracking (SOHIC)

Refiners employ water washing, chemical treatment to reduce hydrogen generation and chemical treatment to reduce hydrogen cyanide in the system to prevent or minimize corrosion and hydrogen activity attack. Nalco Water can help minimize the impacts of corrosion by reducing the formation of hydrogen atoms through the use of uniquely designed filming inhibitor chemistries.