What Are the Causes of Corrosion in Steel Structures of Power Plant Buildings in Coastal Areas?

Power plants in coastal areas play a pivotal role in China’s industrial development, and the industrial structures within them serve as critical infrastructure for ensuring smooth production operations. However, due to the unique environmental conditions of coastal regions and the inherent characteristics of industrial production, the steel structures in these buildings are frequently plagued by corrosion. This not only affects their appearance but also poses a serious threat to structural safety and service life. A thorough investigation into the causes of steel structure corrosion, combined with effective prevention and treatment methods, while emphasizing the importance and necessity of inspection and assessment, is of paramount significance for ensuring the normal operation of power plants in coastal areas.

1. Causes of Steel Structure Corrosion

(1) Environmental Factors

1) High Humidity and Salt Spray

Air humidity is generally high in coastal areas, and large amounts of water vapor easily condense on the surface of steel structures to form a water film. At the same time, salt spray generated by the evaporation of seawater is constantly carried by sea breezes into steel mills or power plants. Corrosive substances such as chloride ions in the salt spray dissolve in the water film on the surface of the steel structures, forming a highly corrosive electrolyte solution that accelerates the electrochemical corrosion process of the steel structures.

2) Temperature Fluctuations

Coastal regions experience relatively large diurnal and seasonal temperature variations. These frequent temperature changes cause steel structures to expand and contract due to thermal effects. Over time, the protective coatings on the surface of steel structures may crack or peel due to thermal stress, exposing the steel substrate directly to the corrosive environment and significantly increasing the likelihood of rusting.

(2) Industrial Production Factors

1) Impact of Emissions

Power plants emit various pollutants, such as exhaust gases and waste residues, during production. For example, acidic gases like sulfur dioxide emitted by power plants form acid rain when combined with humid air. When acid rain falls on the surface of steel structures, it causes corrosion. Particulate matter, such as dust generated by steel mills, may adhere to the surface of steel structures and interact with water vapor and salt spray, exacerbating the degree of corrosion.

2) Equipment Vibration

Some large-scale equipment within the plant generates vibrations during operation. These vibrations are transmitted to steel structures, leading to issues such as loosening of bolts at connection points and cracking of welds. This compromises the structural integrity of the steel framework and also makes these areas more susceptible to the accumulation of moisture and corrosive substances, thereby triggering rust formation.

(3) Factors Inherent to the Steel Structure

1) Material Properties

The corrosion resistance of the steel used in some steel structures is inherently limited. If the steel contains a high level of impurities, such as sulfur and phosphorus, its corrosion resistance is reduced, making it more susceptible to rust in harsh coastal environments.

2) Inadequate Surface Preparation

During the fabrication of steel structures, if surface rust removal is incomplete, residual rust and scale can impair the adhesion of subsequent protective coatings to the steel substrate. Furthermore, improper control of surface roughness hinders the uniform application and proper adhesion of protective coatings, thereby compromising their protective effectiveness.

2. The Importance and Necessity of Inspection and Assessment

(1) Accurate Evaluation of Structural Condition

Through professional inspection and assessment, various advanced testing technologies—such as ultrasonic testing, magnetic particle testing, and coating thickness measurement—can be employed to comprehensively and accurately evaluate the degree of corrosion in steel structures, the integrity of protective coatings, and internal defects in the steel. This helps to promptly ascertain the true condition of the steel structure, providing a scientific basis for subsequent preventive and remedial measures.

(2) Timely Identification of Potential Issues

Conducting regular inspection and assessment allows for the detection of potential hazards—such as early aging of protective coatings or microscopic signs of corrosion on the steel surface—before corrosion problems become apparent. This enables the implementation of preventive measures in advance to prevent further deterioration and effectively extend the service life of the steel structure.

(3) Ensuring Production Safety

Normal power plant operations rely on structurally safe and reliable industrial buildings and structures. Inspection and assessment activities can promptly identify potential hazards that may affect the safety of steel structures, such as reduced steel strength due to corrosion or loosening of connection points. By addressing these hazards in a timely manner, production activities can be conducted in a safe environment, preventing production accidents caused by structural failure.

(4) Supporting Maintenance Decisions

Based on the results of inspection and assessment, specific information regarding the location, extent, and progression of steel structure corrosion can be identified. This is crucial for developing reasonable maintenance plans, such as determining whether to perform localized or comprehensive repairs, and selecting appropriate materials and techniques, thereby ensuring the targeted and effective implementation of maintenance work.

3. Preventive Measures

(1) Appropriate Material Selection

During the initial construction phase of power plants in coastal areas, steel with excellent corrosion resistance should be selected based on environmental characteristics. For example, weathering steel is an excellent choice; through the addition of specific alloying elements, it naturally forms a dense oxide layer in the atmosphere, effectively resisting corrosion. Additionally, for critical components or areas prone to severe corrosion, the use of stainless steel should be considered.

(2) Optimized Surface Treatment

1) Thorough Rust Removal

Prior to the fabrication and installation of steel structures, appropriate rust removal methods—such as sandblasting or shot blasting—should be employed to thoroughly remove rust, scale, and other contaminants from the surface. This ensures compliance with specified rust removal grade standards and lays a solid foundation for the subsequent application of protective coatings.

2) Surface Pretreatment

After rust removal is complete, the steel structure surface should undergo appropriate pretreatment, such as phosphating or passivation, to further enhance the surface’s reactivity and corrosion resistance, thereby improving the adhesion between the protective coating and the substrate.

(3) Application of Protective Coatings

1) Selecting Appropriate Coatings

Based on the characteristics of the coastal environment, select a protective coating system with high weather resistance, high water resistance, and high salt spray resistance. Common combinations include epoxy zinc-rich primers and polyurethane topcoats. The zinc powder in the epoxy zinc-rich primer provides cathodic protection, while the polyurethane topcoat offers excellent weather resistance and decorative properties.

2) Standardizing Coating Application

When applying protective coatings, strictly adhere to construction specifications. Ensure uniform coating thickness and avoid missed or thin spots. Additionally, observe drying times between coats and adhesion requirements to guarantee the integrity and effectiveness of the coating system.

(4) Environmental Control and Maintenance

1) Humidity Control

In steel mills or power plants, indoor air humidity can be reduced by installing dehumidification equipment, thereby minimizing the likelihood of moisture condensation on steel structure surfaces.

2) Waste Gas and Slag Treatment
Improve waste gas and slag treatment systems during production to reduce emissions of pollutants such as acidic gases and dust, thereby mitigating their corrosive effects on steel structures.

(5) Strengthening Structural Design

1) Rational Layout

When designing steel structures, coastal environmental factors must be taken into account. Structural components should be arranged rationally to avoid water accumulation and poor ventilation, thereby reducing the time the steel structure is exposed to humid and corrosive environments.

2) Optimization of Connection Design

Optimize the design of connection points in steel structures by adopting reliable connection methods, such as high-strength bolted joints, and implementing appropriate sealing measures to prevent moisture and corrosive substances from entering the joints and causing rust.

4. Treatment Methods

(1) Surface Cleaning

When rust is detected on a steel structure, the first step is to thoroughly clean the affected areas. Use manual rust removal tools or mechanical rust removal equipment to completely remove surface rust layers and peeling protective coatings until the bright surface of the steel substrate is exposed.

(2) Localized Repair

For areas with minor rust, localized repair methods can be employed. First, reapply a primer to the cleaned area—such as an epoxy zinc-rich primer compatible with the original protective coating system. Once the primer is dry, apply the corresponding topcoat to restore its protective function.

(3) Comprehensive Repair

If the steel structure exhibits severe corrosion over a large area, comprehensive repair is required. This may involve a series of operations, including re-derusting the entire steel structure surface, pretreatment, and application of protective coatings, to ensure the steel structure is restored to a sound protective condition.

(4) Structural Reinforcement

While addressing corrosion issues, if it is found that the steel structure has experienced a reduction in strength or deformation due to corrosion, reinforcement measures must also be implemented. This can be achieved by adding support members or replacing damaged components to ensure the structural safety of the steel structures.

5. Conclusion

The issue of corrosion in steel structures of industrial buildings within power plants in coastal areas is a matter that requires high priority. Through an in-depth analysis of the causes of corrosion, we recognize the importance and necessity of inspection and assessment. Only through regular, professional inspection and assessment can the condition of steel structures be accurately assessed, potential problems be identified in a timely manner, and a basis be provided for implementing effective preventive and remedial measures. At the same time, only by combining reasonable preventive measures with targeted treatment methods can the safety and service life of steel structures be effectively guaranteed, thereby ensuring the continuous operation of normal production activities at steel mills and power plants.