Coatings and Painting for Marine Steel Structures

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The corrosion environment for marine steel structures is extremely harsh, ranging from salt spray and ultraviolet rays to exposure to seawater and wave impact; therefore, their protection requires a systematic approach. Below, we will provide you with a systematic overview of coatings and painting for marine steel structures, covering aspects such as coating systems, painting processes, technical standards, and recent developments. 1. Coating systems for marine steel structures: The environment in which marine steel structures are located can be divided into the marine atmospheric zone, splash zone, tidal range zone, fully submerged zone, and seaweed zone. The corrosion mechanisms vary in different regions; therefore, different coating systems are required for protection. A complete and long-lasting anti-corrosion coating system typically consists of three layers: a primer, an intermediate coat, and a topcoat, which work together in a sequential manner. In addition, there are also special functional coatings designed for specific areas and functions: anti-fouling paints, which are used on the bottoms of ships and underwater parts of platforms. By releasing biological inhibitors such as cuprous oxide, they prevent marine organisms such as barnacles and algae from attaching, thereby reducing sailing resistance or the load on the platform. High-temperature resistant coatings: Used for high-temperature areas on platforms such as flare arms and exhaust pipes (120°C–600°C). Depending on the temperature range, different heat-resistant resin systems such as phenolic epoxy and silicone can be selected. Deck anti-slip coating: Used in areas such as helicopter decks and escape routes; it involves mixing abrasive aggregates like emery into epoxy or polyurethane coatings to create a rough surface with a high coefficient of friction, thereby ensuring the safety of personnel and equipment. 2. To achieve the optimal performance of a coating in key painting processes, three parts depend on the coating itself, while seven parts depend on the application process. Surface treatment: This is the most crucial step in determining the lifespan of the coating, with the goal of achieving a clean steel surface that has a certain level of roughness. New structure: The standard method is sandblasting cleaning, which must achieve the Sa 2½ level (a nearly white surface finish) to completely remove oxide scale, rust, and dirt. Maintenance/Repair: For old coatings or rusted surfaces that are difficult to clean thoroughly, low-surface-treatment coatings can be used. The latest standard T/CSTM 01233—2024 was specifically developed for such conditions, allowing rust-covered painting in high-humidity environments where a Sa 2½ grade cannot be achieved. Main methods for applying coatings: High-pressure airless spraying is the preferred method for applying coatings over large areas of marine steel structures; it is efficient and allows for the creation of thick coating layers in a single application. For complex small parts, brushing or roller coating can be used. Environmental control: The construction environment has strict requirements regarding temperature, humidity, and dew point. For example, two-component polyurethane topcoats are sensitive to water vapor; curing in high-humidity environments can result in bubbles, which affects their performance. 3. Technical standards and certification: Coatings and painting for marine engineering must comply with a range of stringent international and **standards to ensure their reliability. ISO 12944: Corrosion protection of steel structures by protective coating systems is a fundamental standard. GB/T 31415-2015 (ISO 20340:2009): It specifies the performance requirements for protective coating systems used in offshore structures and related constructions, and serves as an important basis for determining whether such coatings are suitable for use in marine environments. NORSOK M-501: A standard for the Norwegian oil industry that sets very high requirements for surface treatment and protective coatings; it is one of the most commonly referenced standards in offshore platform projects. T/CSTM 01233—2024: Chinese group standard for low-surface-treatment coatings used in the maintenance of coastal steel structures, particularly suitable for repair work under limited on-site conditions. 4. New technologies and development trends toward environmental friendliness: As environmental regulations become increasingly strict, water-based heavy-duty anti-corrosion coatings and high-solid-content coatings (such as high-solid-content epoxy and polysiloxane coatings) have emerged as important development directions, as they can significantly reduce the emission of volatile organic compounds. Longevity and high performance: The increasing demands for coating lifespan (15–20 years or more) have driven the use of ultra-high-performance systems such as polysiloxane topcoats, fluorocarbon topcoats, and hot-dip zinc/aluminum composite coatings. Facilitation of construction: Low-surface-treatment coating technologies are becoming increasingly mature, and relevant standards have been established, providing reliable solutions to address on-site maintenance challenges and reduce construction costs. Expansion of application areas: Related technologies are shifting from traditional ships and platforms to emerging fields such as offshore wind power, and ISO is developing anti-corrosion standards specifically for offshore wind power structures (ISO 25249-2). In summary, the corrosion protection of marine steel structures is an integrated technology that combines materials science, surface engineering, and standard management. Selecting the appropriate coating system and strictly adhering to the painting process standards are key to ensuring the safety of marine facilities and extending their service life.