In the ultra‑low emission retrofit of boilers, the denitrification steel structure provides all the load‑bearing and stability functions for the SCR reactor, process piping, and maintenance platforms, serving as a critical framework for the safe operation of the environmental protection system. Compared with conventional boiler main steel frames, denitrification steel frames operate continuously at high temperatures of 300–420°C, are constantly exposed to corrosive environments from sulfur and nitrogen oxides as well as low‑temperature condensate, and must withstand cyclic temperature variations, high‑velocity gas erosion, and prolonged outdoor exposure. As a result, they are highly susceptible to rusting, coating delamination, weld failure, and other issues. The proper selection of anti‑corrosion measures directly determines the service life of the steel frame, the operational stability of the equipment, and the outcome of environmental compliance inspections. Currently, in the industry, anti‑corrosion treatments for boiler denitrification steel structures are mainly categorized into… High-temperature paint coating, epoxy zinc-rich composite coating, hot-dip galvanizing for corrosion protection Three mainstream processes are examined in this paper, with a comprehensive comparison of their respective advantages and disadvantages and applicable scenarios, based on real-world operating conditions.

I. High-Temperature Paint Coating: An Economical Basic Anti-Corrosion Solution

High‑temperature paint coating is the foundational anti‑corrosion method for denitrification retrofitting of small and medium‑sized industrial boilers, characterized by ease of application, low on‑site costs, and flexible adaptability. The complete process involves rust removal, dust removal, and surface preparation, followed by spraying a dedicated high‑temperature‑resistant primer and topcoat; after natural or low‑temperature curing, the coating forms a durable barrier that resists typical high‑temperature oxidation and mild chemical corrosion, thereby meeting the basic protective requirements of low‑corrosivity service conditions.

The advantage of this process is that it requires no large-scale equipment, can be implemented entirely on-site, features a short construction period, and has low retrofitting barriers, making it particularly well-suited for denitrification upgrades in applications with mild operating conditions and limited budgets, such as heating boilers and boilers at small processing enterprises. Moreover, the coating is thin and lightweight, does not obscure steel‑structure welds or component details, thereby facilitating subsequent structural inspections, equipment maintenance, and secondary modifications.

The corresponding shortcomings are also quite pronounced: the coating exhibits only moderate density and adhesion, with weak resistance to acid–alkali attack and condensation‑induced corrosion. When exposed over long periods to high‑velocity gas flow and significant temperature fluctuations, the coating is prone to chalking, peeling, and flaking, resulting in a typical service life of just 1–2 years. This necessitates frequent repainting and maintenance, leading to high cumulative operation and maintenance costs, and rendering it unsuitable for anti‑corrosion protection of denitrification steel structures in high‑sulfur environments or large power‑plant boilers.

II. Epoxy‑Zinc‑Rich Composite Coating: A Widely Used, Industry‑Standard Anti‑Corrosion Solution

Epoxy‑rich zinc composite coating is currently the mainstream choice for large and medium‑sized industrial boilers and denitrification retrofit projects, and it also serves as the standard anti‑corrosion process for environmental protection project acceptance. This system employs a mature three‑layer composite structure—epoxy‑rich zinc primer, anti‑corrosion midcoat, and high‑temperature‑resistant silicone topcoat. The high‑zinc‑content primer provides cathodic protection, effectively preventing steel corrosion at its source; the midcoat thickens the protective layer, enhancing coating adhesion and impact resistance; and the topcoat, specially formulated to withstand the high‑temperature operating conditions of denitrification systems, reliably resists airflow erosion, high‑temperature oxidation, and aging.

Compared with conventional high‑temperature coatings, this process delivers a substantial improvement in corrosion resistance. Its dense, pore‑free coating effectively guards against condensation‑induced corrosion and attack by acidic or alkaline media, while exhibiting excellent high‑temperature stability, weatherability, and resistance to thermal cycling. It is well suited to the denitrification operating conditions of boilers across most industries, including chemical processing, building materials, and medium‑sized power plants. Whether applied to factory‑prefabricated steel frames or on site‑assembled components and welded joints, it can be sprayed uniformly, leaving no uncoated “dead zones,” and offers exceptional ease of application.

Under standard construction and normal operating conditions, this coating system can achieve a service life of 6–8 years, offering an excellent balance between cost and protective performance and delivering exceptional value. However, it places stringent demands on the application environment: humid, rainy, or dust‑excessive conditions can compromise coating adhesion, necessitating rigorous control of both the application process and site conditions to ensure high‑quality corrosion protection.

III. Hot-Dip Galvanizing for Corrosion Protection: A Heavy-Duty, Long-Lasting, High-End Anti-Corrosion Solution

Hot-dip galvanizing is a heavy‑duty, long‑lasting anti-corrosion process specifically designed for highly corrosive environments, heavy loads, and continuous outdoor exposure at ambient temperatures. It is the preferred solution for the auxiliary steel structures of large power‑plant denitrification systems. The process involves immersing finished steel components in a high‑temperature molten zinc bath, where metallurgical reactions between the zinc layer and the steel surface form a dense, stable zinc‑iron alloy protective coating. This results in a seamless, one‑piece structure with no dead angles, providing all‑round protection against atmospheric air, corrosive gases, and moisture.

Here, it is important to highlight the industry’s key knowledge points: The long-term service temperature of hot-dip galvanized components shall not exceed 200°C. Therefore, it is suitable only for ambient‑temperature components such as denitrification platforms, ladders, and outdoor supports, and must not be used on surfaces exposed to high‑temperature conditions. This coating process offers stable protective performance, resisting acids and alkalis, withstanding erosion and abrasion, and preventing aging; it is well‑suited to harsh ambient‑temperature environments characterized by severe sulfur‑induced corrosion, prolonged outdoor exposure, and extreme diurnal temperature fluctuations. Once cured, it requires virtually no routine maintenance, with a service life of 10–15 years, significantly reducing subsequent operation, maintenance, and refurbishment costs.

Its main drawbacks lie in cost and construction constraints: the overall project cost is higher than that of spray‑on coating, and it can only be fabricated in the factory. Any damage occurring on-site during cutting or welding must be repaired by localized re‑plating, further extending the construction timeline. Consequently, this method is not well suited for short‑term, time‑critical, low‑cost small‑scale denitrification retrofit projects.

IV. Summary of Process Selection and Practical Recommendations for the Industry

The three anti-corrosion processes have clearly defined applications and well‑specified use cases; when selecting a solution, there is no need to blindly pursue high‑end options—focus on the core principles. Paint for high-temperature areas; galvanizing for ambient-temperature areas. Principle: For small‑scale boiler denitrification projects involving low temperatures, low sulfur content, and mild corrosion, high‑temperature paint coatings should be prioritized to control retrofit costs. For the vast majority of industrial boilers and medium‑sized power‑plant denitrification retrofits, epoxy‑rich zinc‑based high‑temperature composite coatings are preferred, balancing anti‑corrosion performance, construction efficiency, and cost‑effectiveness. For large‑scale power‑plant components such as outdoor platforms and external support structures that operate at ambient temperature under heavy loads, hot‑dip galvanizing is the first choice, providing long‑lasting, maintenance‑free protection.

The core key to corrosion protection for denitrification steel structures is Operating condition matching + standardized construction Regardless of the process employed, rigorous control over steel surface rust‑removal grade, coating thickness, ambient temperature and humidity during application, and curing procedures is essential to fully prevent issues such as steel‑frame corrosion and coating delamination, thereby ensuring the long‑term stable operation of the denitrification system and its successful compliance with environmental‑protection acceptance criteria.