Corrosion inhibitors ensure corrosion prevention and protection.
Corrosion attack is an omnipresent threat to oil refineries and petrochemical plants. Corrosion is defined as a gradual destruction of a material or substance. Corrosion costs companies around the world billions of dollars. It may lead to significant loss of production, cost of maintenance and expensive repairs. Some technologies increase the corrosion resistance of the distillation equipment. Corrosion resistant alloys (CRA), coating of the metal surfaces or cathodic protection offer good corrosion prevention. Due to its low purchase costs most distillation equipment is made of carbon steel. Carbon steel is very unstable in acids which lower the corrosion resistance of the metal surface. Corrosion rates increase sharply when pH drops down below 7. Corrosive components are hydrogen chloride, hydrogen sulfide, ammonium chloride, ammonium bisulfide, carbon dioxide and organic acids.
Typical corrosion forms in refineries are, in particular:
- Local corrosion or Pitting
- Hydrogen Induced Corrosion (HIC)
- Stress Corrosion Cracking (SCC)
Aqueous corrosion is caused by the electrochemical processes of two half-cell reactions. The basic corrosion cell requires an anode, cathode, metallic conductor and electrolytes. If one of these is missing, aqueous corrosion will not occur. Corrosion inhibitors are used for corrosion prevention. They can help to stop or decelerate the function of a corrosion cell. Filming amines and neutralising amines provide excellent corrosion protection and are well-established treatment programmes.
Film-forming amines are the most common corrosion inhibitors. They form a protective layer on the metal surface. This results in a better corrosion protection by increasing the corrosion resistance. Oil soluble filming amines are well established in oil refineries and petrochemical plants. They need hydrocarbons from the process stream to form a protection layer. They are used in hydrocarbon systems with lower water content. Process systems with high water content are vacuum overheads, sour water strippers, water quench columns or amine units. Water-soluble filming amines offer excellent corrosion protection properties. Kurita provides high-performing oil soluble and water soluble amine for corrosion protection.
Historically, ammonia was used as a neutralising amine. Ammonia has a number of negative properties and increases the risk of ammonium salt fouling. Ammonia is a volatile amine and will not provide a safe neutralization during condensation. Kurita´s modern neutralising amine blends provide excellent corrosion protection and very good buffering capacities. They operate by reacting with any acid constituent in a straight forward chemical neutralization. The neutralising amine shifts the pH from very corrosive conditions to levels which are easier to control. They demonstrate an easier pH control and better handling.
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