Eliminating Corrosion Issues in Different Types of Power Plants

Corrosion in the electric power industry costs the U.S. over $23 billion per year. With plants looking to increase efficiencies, lower costs, and reduce the amount of time offline for maintenance, corrosion prevention techniques will help lengthen the life of various components and increase safety. While many thermal power plants share the same types of corrosion issues, some require different preventive approaches.

Common Types of Corrosion

• Oxide corrosion: An electrochemical process that occurs when metal is exposed to water and changes in composition.
• Galvanic corrosion: A process that occurs when two dissimilar metals contact each other; the resulting electrical reaction leads to and accelerates corrosion.
• Erosion: The result of an aggressive chemical environment combined with high fluid surface velocities that ultimately wear away a surface’s protective scale or coating.

Corrosion in Thermal Power Plants

Thermal power plants—including geothermal, coal, nuclear, natural gas, and solar thermal electric plants—generate steam to drive turbines that spin electrical generators, or dynamos. These types of plants have similar components that operate at different pressures and temperatures, such as:

• Boilers: Tubes that heat water to produce steam
• Steel drums: An area where water forms a steam
• Feedwater heaters: Heaters with water inside the tubes and steam outside the tubes
• Superheater: A component that heats steam to higher temperatures
• Turbine: The area where steam expands against wheel vanes to drive the turbine
• Pipes: Carry hot or cold water, steam or gases
• Cooling tower: Eliminates waste heat into the atmosphere by cooling water to a lower temperature

Corrosion at thermal power plants poses safety hazards that may be fatal if a worker is exposed to hot steam, gas, ash, or radioactive materials from a leaky component or welding failure. In addition to driving up maintenance costs, if corrosion prevents a plant from starting after scheduled maintenance, the operators may face non-delivery fees.

Fossil Fuel Plants

Fossil fuel plants have unique corrosion issues when they have buried storage tanks for fuel and underground piping systems. In such an instance, galvanic corrosion formed by dissimilar metal couples becomes problematic in older plants if they lacked cathodic protection or have undocumented connections. Newer plants use solid-state DC decoupling devices as galvanic corrosion prevention.

Nuclear Plants

Heat transfers in nuclear steam plants involve the use of pressurized light water, heavy water, and other types of media. Corrosion prevention is critical in nuclear plants because failures or leaks in a radioactive component pose a radiation hazard to personnel and the area surrounding the plant. Corrosion could also lead to metal losses that release radioactive materials or component failures.

Corrosion Control in Thermal Power Plants

• Generators: Maintain low humidity levels of 35 percent or lower using a closed-loop system.
• Pipes: Install insulation with a jacket or protective coating, replace pipes with more resistant materials or improve the piping design so it has better flow geometries.
• Water chemistry changes: When chemicals or organic agents in the water (e.g., anaerobic bacteria) lead to corrosion, a water-conditioning agent may be helpful. Replacing steel components with composite lines may also be effective, particularly in nuclear plants.
• Turbines: Seal openings as tightly as possible.
• Controlling water and steam: Use drains or vacuums to prevent water pooling. Dehumidifiers are good for air that passes through a turbine, drying pockets of water and reducing relative humidity (rH) levels.
• Oil-fired boilers: Use an open system and a dehumidifier to dry the air to 20 percent rH after shutting down a boiler.
• Protective coatings: Use protective coatings on components exposed to water, the outside environment, or in areas that may experience condensation or moisture. Protective coatings or surfaces are also helpful for preventing erosion-related wear.
• Cooling stacks: Install a windshield or protective liner to prevent chemical attacks and thermal shock.
• Inspections: Regularly inspect and test components that are at risk for corrosion, even if they have protective surfaces. Such components include turbines, ducts, pipes, welded areas, areas with demineralized water, and scrubber modules.

Water is essential to running a power plant. At the same time, water can cause vital components to fail when the materials oxidize. By preventing and controlling erosion at a plant, you’ll reduce maintenance costs and downtime, improve performance and increase worker safety. Polygon has a variety of temporary climate solutions that will aid maintenance tasks and protective coating applications. For more information, get in touch with a Polygon specialist today.

[Photo by 24x7photo.com via CC License 2.0]