What Does Mesa Corrosion Mean?
Mesa corrosion is a common type of corrosion where low alloy steels and carbon are exposed to conditions of wet carbon dioxide at elevated temperatures. This results in the formation of an iron carbonate surface which shields the rest of the material from corrosion.
Shear forces are produced by the moving gas under the surface, which damages the scale, thus removing it to expose the fresh metal to conditions of corrosion. This is a localized attack that produces mesa-like features from the corrosion of the active regions to leave behind the passive regions.
Corrosionpedia Explains Mesa Corrosion
Mesa corrosion is characterized by the sharp pits that appear in the form of sharp-edged holes which look like the United States' Mesa Mountains. When the local breakdown of the protective corrosion films occurs, mesa corrosion attack is evident during the CO2 corrosion of carbon steel. The affecting factors that result in the local breakdown of the protective films can be studied at 40°C - 80°C, with 1.8 bar CO2 partial pressure, a pH of 5.8, high iron water content and flow rates of between 0.1 and 7 m/s.
Testing of carbon steels with or without chromium and nickel additions of up to 1 should be done. 0.5% of chromium in steel reduces the severity of the mesa attack. A deep mesa attack does not occur in steels with 0.5% - 1% chromium at a pH of 5.8 and a temperature of 80°C. It should be noted that the protective corrosion films tend to reform quickly and easily when chromium is present in steels.
The most common control methods for mesa corrosion are:
- Use of corrosion inhibitors: They contain surface active compounds that prevent corrosion and adhere to the surface.
- Application of hydrate preventer: Most of these, such as glycol, reduce the rate of corrosion by reducing the concentration of water on the material.
- Reduction of the water wetting: This depends on the type, density, viscosity and the temperature of the oil.
- Increase the pH: This gives the best correlation with the rate of corrosion.
- Reduction of the CO2 pressure: This is done through choking where the reduction of pressure by half reduces the corrosion rate at a lower rate.
- Avoiding flow disturbances: Welding methods and other construction procedures are selected to give minimal flow disturbances.