Petrochemical products have a significant role in everyday life. Without them, fuels, solvents, drugs, clothing, flooring, insulation, beauty products, electronics, and other products that you rely upon might not exist. Before these products enter homes and businesses, crude oils and fuels sit in steel storage tanks that are vulnerable to corrosion. Corrosion control programs that include regular maintenance, inspections and proper surface preparation for coating applications enhance the safety of workers while protecting the integrity of the raw materials.
Characteristics of Fuels and Crude Oil
Crude oil is a mixture of hydrocarbons found in the Earth’s crust. After the raw materials undergo distillation, the mixture is separated based on the boiling points of its components. Purification and different treatment processes allow distillates to become the different petrochemical products used today.
Chemical compounds in crude oils contribute to its corrosive nature. Such compounds include:
- Dissolved hydrocarbon gases
- Hydrogen sulphides
- Aromatic hydrocarbons with one or more aromatic rings
- Waxes
- Alkanes
- Cycloalkanes
- Heteroatomic compounds with nitrogen, sulphur, and oxygen
- Metals (e.g., aluminum, potassium, sodium, nickel, vanadium, calcium and copper)
- Inorganic salts
Mercaptans and suphildes are major corrosive substances in petrochemical products. The corrosive nature of sulphur-containing compounds increase as the temperature of crude oil rises. As temperatures warm, metal sulphides, hydrogen sulphide and organic molecules form, causing pitting, uniform corrosion, sulphide stress corrosion, and erosion corrosion. Naphthenic acids also present corrosive dangers at refineries.
Enhancing Tank Safety with Corrosion Control
With proper surface coatings and maintenance, crude oil tanks are safe. When the coatings fail, corrosion can damage several millimeters of tank components per year, depending on the location. In addition to oil and fuel leaks, corrosion may also lead to dangerous accumulations of hydrocarbon gases and vapors. The Occupational Safety and Health Administration reports that the gases and vapors create oxygen-deficient atmospheres and increase the risk of explosions and fires, which contribute to worker injuries and deaths.
Corrosion control begins with storage tank engineering and design, as it should promote the adhesion of coatings and corrosion inhibitors. Corrosion management also includes meeting standards related to cathodic protection, antibacterial treatments, coatings, surface preparation for coating applications, corrosion inhibitors, and other technological measures. Of equal importance is corrosion monitoring that allows workers to determine an environment’s corrosiveness, the state of the materials and the effectiveness of corrosion mitigation efforts.
Protective Coatings
The most common type of surface protectant used on aboveground storage tanks and underground storage tanks are organic epoxy coatings. In addition to preventing corrosion, the coatings reduce volatile organic component losses, maintain quality levels, reduce wear to tank components, and help protect the environment. Shell coatings also significantly extend rim seal life.
When tanks contain naphtha and gasoline, they may also contain antistatic, non-conductive or electro-conductive coatings to reduce static electricity caused by aboveground tank floating roofs. These protective coatings often contain nickel oxide, zinc, aluminum and graphite to increase their electrical conductivity and give them antistatic properties.
The majority of coating failures are not due to the coatings themselves, but their improper application because of poor surface preparation techniques. Proper surface preparation for coating applications involves more than cleaning tank surfaces well. It also requires maintaining an environment that prevents recontamination and the formation of condensation, maintains appropriate relative humidity levels, promotes ventilation, and controls air and tank surface temperatures.
Because the weather is unpredictable, the petrochemical industry looks to temporary climate control solutions, such as those designed by Polygon, to create an environment that’s conducive to successful tank surface preparation and coating projects. When paired with other corrosion control methods, climate control technologies for surface coating projects protect one of the industry’s greatest assets—its workers.
[Phil Parker via CC License 2.0]
