Application Status and Development Analysis of Heavy-duty Anti-corrosion Coatings for Marine Engineering

Marine anti-corrosion is one of the key technologies of marine engineering. The stress corrosion cracking (SCC), hydrogen embrittlement (HE), corrosion fatigue (CF), intergranular corrosion (IC) caused by corrosion of metals in the ocean will make marine steel. Sudden breakdown of the structure leads to ecological disasters in the marine environment, causing huge losses. In addition, the early failure of the anti-corrosion coating of marine products and the loss of workmanage caused by coating maintenance are also considerable. Therefore, it must be solved by appropriate anti-corrosion techniques.

In recent years, marine corrosion and protection have become more and more important at home and abroad. Although various seawater resistant materials have been continuously introduced, various anti-corrosion construction technologies have also developed greatly, but they are still far from meeting actual needs. China's anti-corrosion research on offshore engineering structures and facilities has obvious gaps with foreign developed countries. Some key technologies have not yet been resolved. There is no technology with independent intellectual property rights in China, and there is no corresponding anti-corrosion norms and standards, which have seriously affected the oceans. Design, construction and safe operation of engineering structures. Therefore, in view of the commonality and key anti-corrosion problems faced by China's key sea areas and major marine projects, the research on key technologies for long-term anti-corrosion of offshore engineering structures will not only prevent corrosion, but also avoid or reduce the maintenance and maintenance costs of later service. It is of great significance to reduce the economic losses caused by maintenance, reduce the occurrence of major malignant accidents, and greatly improve the safety of offshore facilities.

1 Marine anti-corrosion coating requirements Marine anti-corrosion coatings refer to anti-corrosion coatings used in the marine environment. Because the marine environment is very harsh and highly corrosive, marine anti-corrosion is an urgent need for serious research in the development of marine engineering in China.

According to the material and corrosion mechanism of the anti-corrosion object, the marine anti-corrosion coating can be divided into marine steel structure anti-corrosion coating and non-steel structure anti-corrosion coating. Marine steel structure anti-corrosion coating mainly refers to anti-corrosion coatings for large-scale facilities such as transportation ships, containers, sea bridges, port machinery, oil pipelines, offshore oil platforms, etc. Non-steel structure marine anti-corrosion coatings mainly refer to marine concrete structures anti-corrosion coatings.

Marine anti-corrosion coatings mainly include inorganic zinc-rich, organic zinc-rich, silicone, epoxy, acrylic, polyurethane, fluorocarbon, and silicone coatings. Different coatings and coatings can be selected according to different marine environmental corrosion characteristics and corrosion protection years. system. Marine anticorrosive coatings generally require the following properties:

1 has good physical properties. Good corrosion resistance to corrosive media and good adhesion to steel surfaces;

2 has good mechanical properties. Seawater scouring, sea ice collision resistance, and resistance to ship wear;

3 has excellent chemical properties. Resistance to seawater, salt spray, oil, chemical, UV, etc.;

4 Compatibility with electrochemical protection systems. Spatter zone and full immersion zone paint should have cathodic disbonding resistance;

5 has good construction performance. High quality painting and construction of different structures under various environmental conditions;

6 meet the requirements of health, environmental protection and safety. Requires high solids content and volatile organic compound (VOC) content in accordance with national or international standards;

7 other special requirements. For example, fresh water tank coatings are non-toxic and meet the national sanitation certification requirements; the chlorine content in the coating for stainless steel surface should not exceed 200 mg/kg, and the coating does not contain zinc; the ship's ballast tank coatings must conform to international standards. Maritime Safety Administration (IMO) requirements for “Performance Standards for Protective Coatings for Ships' Ballast Tanks”; coatings for ships below the waterline are required to prevent the attachment of marine organisms.

The main relevant international standards for commonly used marine heavy-duty coatings are:

1ISO 12944 protective coating system for corrosion protection of steel structures;

2NORSOK M501 surface treatment and protective coating;

3ISO 20340 performance requirements for offshore and related structural protective coating systems;

Corrosion control of 4NACE SP O108 protective coating on offshore structures;

5IMO Ship Ballast Tank Protective Coating Performance Standard (PSPC).

Marine anti-corrosion coatings and their coatings are usually required to meet the requirements of ISO 12944, NORSOK M501, NACE SPO108 and ISO 20340 related corrosion protection standards. Generally, strict corrosion tests and certifications must be passed in advance. The main test items are:

1 salt spray resistance (brine) test 4 000 h;

2 cathodic disbonding test;

3 resistance to heat and humidity test 4 000 h;

4 cycle corrosion test 4 200 h.

2 Marine anti-corrosion coating research and development Key marine anti-corrosion coating research and development has high technology content, long development cycle, large investment, high technical difficulty and high risk. The research and development of foreign marine anti-corrosion coatings are mainly concentrated in large companies with strong strength or government-supported departments. For example, UK IP, PPG in the United States, Hemple in Denmark, Jotun in Norway, and Kansai Paint in Japan have hundreds of years of relevant paint development history, in coating production supply, quality supervision, coating specifications and coating. The installation site management has formed a set of very strict and rigorous systems. At present, the products of these companies occupy the main market of marine anti-corrosion coatings in China.

The production of marine anti-corrosion coatings in China is mainly concentrated in several coating enterprises such as Qingdao, Shanghai, Dalian, Tianjin, Changzhou, Guangzhou and Xiamen. The research work is mainly concentrated in the Institute of Ocean Research of the Chinese Academy of Sciences, the Institute of Metal Corrosion of the Chinese Academy of Sciences, the Institute of Marine Chemical Industry, and CNOOC. Changzhou Coating Research Institute, China Shipbuilding 725 and other research institutions. In recent years, although the quality management supervision institutions such as “China Shipbuilding Marine Coatings Xiamen Inspection Station” and “Marine Coating Product Quality Supervision Center” have been established, the overall technical level still lags behind advanced countries.

At present, the research and development of foreign marine heavy-duty anti-corrosion coatings mainly focuses on the following aspects.

2.1 Long life Because more and more super-large steel structures and the characteristics of the sea area do not have the conditions of direct recoating or returning to the shore, it is required to develop marine anticorrosive coatings with long service life, and the ideal one is the service life of the coating. The continuous service life including direct on-site painting and repair is equivalent to the service life of steel structure equipment, that is, the coating and equipment have the same life design, and only a small amount of maintenance is needed during use, and no recoating is required.

Belgian coating galvanizing is an organic high-zinc-rich coating with a zinc content of 96% in the dry film. In the coastal marine atmosphere of Oslo, Norway, a single zinc coating with a film thickness of 120 μm coated on a steel bridge 15 After a, the average annual coating loss is only 1μm.

The most typical successful application of inorganic zinc-rich coatings is the 250 km tubing project in Morganwyalla, Australia. The anti-corrosion coating uses a single layer of water-based inorganic zinc-rich coating. The coating has remained in good condition for more than 50 years without corrosion. The EXXON company's refinery in Sulphur Ball Island uses a single-layer zinc silicate anti-corrosion coating. After 15 years, only a small part of the coating is required to be repaired. After the replenishment, it is completely rust-free after 4 years.

As a top coat, the weather resistance of currently developed fluorocarbon coatings and silicone coatings can reach more than 15 a, such as chlorotrifluoroethylene FEVE fluorocarbon paint produced by Asahi Glass Co., Ltd., and tetrafluoroethylene FEVE fluorine produced by Daikin. Carbon paint, acrylic polysiloxane coating interfine 979 produced by International Paint Company, and epoxy polysiloxane coating PSX 700 produced by American Ameron Company.

2.2 Low surface treatment Since the pre-painting treatment cost will account for 60% of the total coating cost, low surface treatment coatings have become one of the important research directions of anti-corrosion coatings. It mainly includes rust-bearing, wet-coated coatings and coatings that can be applied directly to other types of old coatings. These coatings are mainly epoxy. They have the function of direct coating on the surface of wet rusted steel. They have excellent adhesion, VOC content <340 g/L, and the thickness of airless spray coating can reach 200μm or more. Excellent construction performance.

2.3 High solids, solvent-free volume solid content above 70% for high solids coatings, solid content of 100% for solventless coatings. Due to the low or no use of organic solvents, high solids coatings can reduce VOC emissions, meet environmental requirements, and obtain the required film thickness in one construction, thus reducing the number of construction roads, saving recoating time, and improving Work efficiency. Since the solvent-free volatilization reduces the porosity of the coating, the impermeability and corrosion resistance of the coating are improved.

2.4 Water-based coatings are another important aspect of coating development. Its low VOC content is important for energy conservation and emission reduction, development of a low carbon economy, environmental protection and sustainable development. At present, the research and development of water-based coatings are mainly in the fields of water-based inorganic zinc-rich, water-based epoxy, water-based acrylic acid, and water-based fluorocarbon systems. The industrial application of water-based acrylic acid, water-based epoxy and water-based inorganic zinc-rich coatings has been successful to some extent. Japan's Asahi Glass Co., Ltd. has developed a new low-VOC water-based FEVE copolymer, which is comparable to solvent-based fluorocarbon paints in its weather resistance, water resistance, solvent resistance and gloss.

In March 2008, at the anti-corrosion seminar organized by the American Society of Corrosion Engineers (NACE), Hydro Petroleum of Norway tested and evaluated the waterborne coatings according to NORSKOK M-501. The results showed that the waterborne coatings were in the oceanic environment. There is an encouraging application prospect in the field of painting and repairing new facilities.

2.5 Environmentally-friendly new materials Environmentally-friendly new materials mainly use low-toxic, non-toxic materials, such as the replacement of toxic and polluting red dan, chromate and other anti-rust pigments with composite phosphate anti-rust pigments, strictly control the lead in the pigment, The content of heavy metals such as cadmium, chromium, mercury and arsenic.

The US Department of Energy's Brocawin Laboratory has developed a bio-heavy anti-corrosion coating based on cereals, crab shells, and lobster shells. Under appropriate temperature conditions, the coating becomes firm, smooth, and adheres tightly to aluminum or Other metal surfaces prevent corrosion of the metal.

2.6 Polyurea elastomer Polyurea coating is a solvent-free, non-polluting high-performance heavy-duty anti-corrosion coating that has emerged in recent years, referred to as SPUA. SPUA is two-component, 100% solid content, environmentally friendly, its curing speed is fast, it is not sensitive to humidity and temperature, and it is not affected by environmental humidity during construction. The film elasticity and strength, weather resistance and thermal stability after curing Excellent, outdoor long-term use does not crack, does not fall off, has good adhesion to steel, and has excellent corrosion resistance. However, SPUA has extremely strict requirements on the surface treatment of the coated substrate. The steel should be thoroughly sandblasted and must be applied immediately after treatment.

It has been applied to the anti-corrosion of offshore structures in the United States and Taiwan, especially in the splash zone of offshore platform steel structures. Polyureas mainly include aromatic polyureas, aliphatic polyureas, and polyaspartate aliphatic polyureas.

3 Marine anti-corrosion coating coating analysis and recommendations 3.1 Coating application status and problems At present, most of the anti-corrosion coatings used in marine engineering are products of foreign multinational companies, and domestic coating products are rarely used. Regardless of the quality of coating products or the quality control mechanism, there is a big gap between domestic coating products and foreign products. The main reason is that China's marine anti-corrosion coatings have short development time, lack of core technology, lack of research funds, and low level of researchers. These shortcomings have greatly restricted the entry of domestic coatings into the international offshore market and weakened domestic production. The competitiveness of the brand.

Based on the use environment of offshore products, it is necessary to take anti-corrosion protection measures. For offshore anti-corrosion coatings of offshore products, it is difficult to repair or recoat at sea during the service period, prolonging the durability of anti-corrosion coatings. And the anti-corrosion coating and the life of marine products are the ultimate goal of marine anti-corrosion research. Therefore, the research and development of marine heavy-duty anti-corrosion coatings and coating technology with a durability of more than 15 years in the marine environment, designing a metal coating + organic coating system that can achieve a durability of 15 to 30 years in the marine environment, multi-layer organic Or the inorganic coating supporting system is not only the focus of research on marine anti-corrosion needs of national marine development strategy, but also the research direction of marine anti-corrosion coating technology work in the national “12. 5” plan, and the development of high efficiency of cathodic protection. The lacquer, good intermediate coating and weather-resistant topcoat, as well as the appropriate coating design, are the key to the anti-corrosion coating system.

Marine anti-corrosion coatings are currently mainly used to prevent corrosion of structures exposed to the marine atmosphere. Submerged parts of sea structures, such as marine structures (such as ships and rigs) and submarine steel pipes, which are immersed in seawater, especially in deep water areas, also require coating protection. corrosion. Due to the low oxygen content and relatively low corrosion level in this area, epoxy coatings, epoxy asphalt coatings, epoxy glass flake coatings, etc. are mainly used. If it is necessary to prevent sea organisms from adhering, epoxy coatings + antifouling coatings are used. Combination system. For the submarine area, the coating is mainly made of epoxy asphalt coating because of the lowest degree of corrosion in this area. In addition to liquid epoxy coatings, steel pipes also use a large amount of molten epoxy powder coatings. Due to the extremely difficult maintenance, it is usually required to be used normally for more than 20 years without maintenance.

Anti-corrosion coatings used in seawater are generally required to have good resistance to sea creatures and chemical stability to ensure that the coating can resist fouling and corrosion; have good mechanical strength to ensure that the coating can withstand certain pressures and collisions. Keep the integrity of the coating so that it does not crack or fall off; it should have good adhesion to the surface of the steel pipe and concrete; the external cathodic protection system has good compatibility, and the coating does not peel off when using cathodic protection.

Coating anti-corrosion and coating + electrochemical corrosion protection is the main method of marine anti-corrosion. Compared with the anti-corrosion performance of the coating, the construction performance and repairability of the coating in seawater are more important. Therefore, it is generally recommended to design the coating life to be the same as the coated structural body or maintenance-free. In addition, the use of anti-corrosion coatings that can be applied in water is also the direction of current efforts. Many companies in foreign countries have developed such products, which are usually liquid high-solid epoxy coatings.

Shipbuilding is an industry that uses marine anti-corrosion coatings in marine engineering. The coating technology of China's marine anti-corrosion coatings has also achieved rapid development and reached a certain level. For example, the coating process has been listed. One of the important contents for ship design; the steel pretreatment process has been widely used in shipbuilding enterprises, and a staged descaling and painting workshop has been established, and corresponding automatic and semi-automatic descaling and spraying equipment have been equipped, and a series of Technical standards for rust and coating; practitioners have mastered the high-performance coating construction process and special coating technology for chemical/product tankers; computer-aided coating design and treatment technology, and regional coating technology have been promoted in large shipyards.

The application of new coating technology has greatly improved the level of coating technology, production efficiency and coating quality in China, and significantly shortened the gap with foreign coating technology. The quality of coating has been well received by ship owners at home and abroad. However, there is still a big gap between China's ship coating technology and foreign countries, mainly in the following aspects:

1 The design depth of the ship's painting production is not enough, and the concept of shell coating integration is not strong;

2 The degree of mechanization and automation of ship coating technology and equipment is not high, resulting in more rust and coating indicators being executed;

3 Pretreatment quality and shop primer performance need to be improved;

4 The problem of multiple paintings caused by damage to the coating film caused by other types of construction is very prominent. The lack of technology and talent is one of the important reasons hindering the overall progress of the coating coating industry.

3.2 The solution to the problem The marine engineering anti-corrosion involves the strategy of national marine development. Therefore, it is hoped that the relevant national departments or industry organizations will take the lead in organizing relevant units and integrating social resources at the national level, and the marine anti-corrosion coatings and coating technologies need to be solved. Key challenges to carry out collaborative research and provide strong financial support. It is recommended to strengthen research in the following areas:

(1) Strengthen basic research and improve the level of anti-corrosion coating products. In order to reach a new level in China's marine anti-corrosion coatings, all relevant institutions and coatings manufacturers should strengthen the development of new products, pay attention to the development of high weathering supporting coating systems, the development of high-efficiency and low-toxic anti-corrosion coatings and the environmental protection of marine anti-corrosion coatings. .

(2) Strengthen the research of paint coating process. From the integration of paint coating, we pay attention to the research of coating construction performance, continuously optimize and improve the comprehensive performance of coating products, develop coatings with good adaptability and improve the scientific and rationality of supporting coating systems to adapt to different offshore engineering. Different coating requirements for the product. Usually the paint coating integration is carried out by a third party, that is, the offshore builders outsource all their painting production to a professional coating engineering company, a third party, who is solely responsible for supervision and inspection. At present, some powerful coating companies and coating equipment companies have launched the BOT service model, that is, the construction workshop of the offshore construction company is invested and constructed by the coating company or the coating equipment company, and is responsible for production management, according to the offshore construction company. The production plan is to carry out the coating production, realize the integration of the coating and coating, and finally provide the qualified coating instead of the liquid or powder coating, and the offshore builder only needs to formulate the technical standard and the quality of the inspection and supervision of the coated product. The quality of the coating and the area of ​​the coating are settled. This mode will become the development trend of paint coating integration.

(3) Improve the anti-corrosion performance and construction performance of marine anti-corrosion coatings, strengthen the development of high-temperature ablation (>800 °C) shop primer, solvent-free anti-corrosion coating with high solid content, low viscosity characteristics and convenient construction, better performance Self-drying or low-temperature drying of water-based inorganic zinc-rich primer, water-based acrylic acid, epoxy anti-corrosion coating and epoxy-based thick coating which can be coated at one time with 300-500μm, heavy-duty anti-corrosion coating which can be applied under water. One-component zinc-rich primer and moisture-curing polyurethane anticorrosive coating with better corrosion resistance, inorganic or inorganic modified anticorrosive coating with better corrosion resistance and aging resistance.

(4) Most of the offshore structures are large in size. At present, most of the coating construction is carried out in the open air. Manual spraying is the main coating method. The coating efficiency is low and the quality is difficult to guarantee. Therefore, mechanized coating is the main direction of its development. Pipe fittings, rods, steels and box girder with large number and shape specifications for marine products such as port machinery, platforms and special ships can be painted by shot blasting and painting mechanized production lines, which can greatly improve production efficiency and ensure Painting quality, shortening the construction period and protecting the environment. For components with a relatively simple shape and a large number of parts, it can be painted by an online robot or electrostatically sprayed. For manual brushing and roller coating with low coating efficiency, paint brushes or paint rollers capable of automatically supplying paint should be developed to improve efficiency. Similar products have been obtained abroad.

(5) Strengthen the training of professional talents. In the final analysis, market competition is the competition of talents and the competition of management level. The weakest link of our national defense coatings and coating enterprises compared with similar foreign companies is here. At present, most of the personnel engaged in paint coating technology are converted from chemical or mechanical majors. Due to professional setting reasons, there are very few people specializing in metal corrosion protection. Therefore, many people know that there are few people, and they lack it. An engineering researcher with comprehensive knowledge of coatings and anti-corrosion research and proficient in painting construction technology. There are only a handful of institutions that train metal anti-corrosion professionals in China, which cannot meet the needs of the industry and need to expand the scale of personnel training. At the same time, the painter is the final implementer of the coating process, and its technical quality will directly affect the coating quality and even the anti-corrosion performance of the film. At present, most of the people who are painting and constructing in the first line are untrained migrant workers, and their professional knowledge is lacking. Therefore, it is also an urgent problem for the painting industry to train qualified painters, especially spray operators. It is recommended to carry out systematic social and internal professional education training, for example, training according to the painter's training program to achieve intermediate or advanced painting quality. In addition, the implementation of certification is also an important way to improve the quality of construction workers and the quality of painting.

(6) Painting inspection is the final link to ensure the quality of painting. It is also a very important link and must be carried out by qualified inspectors. The marine products are used in harsh environments and have high requirements for anti-corrosion. Generally, those who require coating inspections for offshore products and international standards must be trained in NACE, SSPC, FROSIO coating inspection and obtain corresponding professional qualifications. Level 2 or Level 3 is required for this work. In this aspect, China should introduce foreign related training materials, train full-time paint inspection personnel in accordance with foreign standards, implement the coating inspection qualification certification system in the marine anti-corrosion coating project, improve the domestic coating inspection level, and improve the coating of marine engineering. quality.

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