Research progress of heavy anticorrosive coatings in the structure of marine engineering steel

The ocean has rich natural resources, andit provides a space environment for human survival. The ocean accounts forabout 70% of the surface area of the earth, which provides rich resources forthe survival and development of human beings. China is not only a vastterritory, but also a wide area of China's jurisdiction. The area of the seaarea is equivalent to the 1/3 of the land area of our country. In addition, theisland coastline stretches as long as 50 thousand km, and there are four majorwaters in Bohai, the Yellow Sea, the East China Sea and the South China Sea.Among them, there are 6536 islands in the sea area above 500 m 2, and 223 kmterritorial sea area is 370 thousand km 2, and the area under its jurisdictionis 370 thousand km, 2 of the exclusive economic zone, the territorial sea, thecontiguous area and the part of the international seabed area. There areabundant marine natural resources in this wide area, and the development ofmarine resources is an emerging field with important strategic significance.With the further exploitation of land resources, it has become increasinglyexhausted. The ocean has become an important pillar for human survival anddevelopment. The development of marine resources is a long way to go.

The electrical conductivity of the seawater is very strong, it contains abundant chloride and sulfate electrolyte,and it is a kind of natural corrosion agent with strong corrosiveness. Underthe action of mechanical stirring and strong natural convection, sea water issaturated by oxygen, so ordinary steel materials will be seriously corroded inmarine environment. For example, it will cause huge economic losses for portmachinery and equipment, offshore platform steel frame, steel Zhanqiao andsteel pile wharf and other large-scale offshore engineering steel structures.Therefore, it is a long way to explore the corrosion protection means of highefficiency and stable marine engineering steel structure.

In this case, the most important thing isto apply the heavy anticorrosion coating outside the steel structure. Heavyanticorrosion coating is a kind of anticorrosive coating, which is the mostrepresentative, powerful and influential in anticorrosion coatings, and hasgreat potential for development. In this paper, the marine heavy anticorrosioncoatings and the development and direction of research at home and abroad aresystematically introduced.

1. Corrosion status of steel structure inMarine Engineering

The steel structure of the marineengineering is the structure of the marine engineering structure, which ismainly based on the steel material. According to the statistics, the output ofsteel is more than 1 billion t a year, and the annual output of steel equipmentis about 30% of the annual output of steel equipment that is only abandonedbecause of corrosion. The number of marine engineering buildings is increasingwith the gradual development of the marine resources. For example, seaport, oilproduction platform, artificial island, seabed pipeline, etc. Therefore, it isof great significance to the development of the country to study the corrosionprotection technology of steel materials to reduce the loss caused by marinecorrosion to the national economy. Seawater, a complex natural corrosionmedium, will cause great damage to the metal structure in it. It is a saltelectrolyte which contains a large amount of sodium chloride. It is alsodifferent from simple salt solution, which also contains suspended sediment,dissolved gas (O 2, CO 2, etc.), biological and corrupt organic matter.Therefore, the marine corrosion and protection of the marine engineering steelstructure is a complicated and severe problem.

The oceans of the world are like a large,interconnected balance. In the marine environment, even the same site in thesame sea will show different corrosion characteristics, which is the complexityof the marine environment. The marine corrosion environment can be divided into5 zones, respectively: atmospheric zone, splash zone, tidal zone, immersionzone and sea area. The corrosion of marine engineering steel structure indifferent corrosion zone shows different characteristics. The corrosion rate ofsplash and tidal zone is the highest, the largest on the corrosion protectiontechnology difficulty. Take different protection measures for different zones,such as coating, coating, electrochemical protection petrolatum anticorrosivetechnology and material modification etc.. The heavy anticorrosion coating isan effective and important means of corrosion protection.

2. Research status of heavy anticorrosivecoatings

Heavy duty anticorrosive coatings can beapplied in relatively harsh corrosive environments. Compared with conventionalanticorrosive coatings, a kind of anticorrosive coating with longer protectionperiod has long service life and can be used in harsh corrosive environments.Compared with ordinary coatings, high coating thickness can be obtained by thefirst spraying of heavy anticorrosion coatings. Its technology content is highand difficult. It involves many aspects of comprehensive technology, not onlydepends on the experience and knowledge of coatings, but also is theinterdisciplinary and interdisciplinary integration of knowledge. Thedevelopment level and performance of the heavy anticorrosion coatings havebecome a symbol of the advanced technology of anticorrosion coatings and anational level of science and technology. The structure of the marineengineering steel has to withstand the challenge of harsh corrosion conditions,which requires stronger adhesion, impact resistance and acid resistance. The heavyanticorrosion coatings have different classification methods according to thedifferent standards. The following is the classification of solvent based andnon solvent heavy duty coatings based on solvents, and the development of nanomodified coatings is also introduced.

2.1 solvent type heavy anticorrosioncoatings

The VOC (volatile organic compounds) inpaint is the total volatile matter content in the coating, which is deductedfrom the moisture content. It is considered that the content of volatile organiccompounds in the coating, and it will cause great harm to human health. WhenVOC reaches a certain concentration, people will feel dizzy, headache, nauseaand fatigue in a short time. Severe coma and convulsion will cause injury tothe kidneys, liver, brain and central nervous system, which will cause memoryloss and other consequences.

At present, most commonly used marine heavyduty coatings are solvent based coatings, because solvent based heavy dutycoatings are easy to get, good performance, good adhesion, tough and wearresistance, no cracks and chemical corrosion.

The main varieties of solvent coatings areepoxy and epoxy ester coatings, alkyd resin coatings, polyurethane coatings,silicone and fluorocarbon resin coatings, acrylic resin coatings, etc. Thefollowing is the most representative of the epoxy and polyurethane heavyanticorrosive coatings.

A epoxy resin coating

Epoxy resin coating is a kind of solventtype heavy anticorrosion coating, which is the most widely used and the largestdemand. Epoxy resin is a linear structure of polymer materials. It has goodstability, adhesion, insulation and mechanical strength, and also has goodalkali resistance and oil resistance. In 1930, the epoxy resin was firstsynthesized by Pierre Castan in Switzerland and SOGreenlee in the UnitedStates, and industrialized production was realized in 1947. Because epoxy resinis difficult to dissolve in aqueous solution, organic solvent is expensive andvolatile. Some of them are also toxic and VOC are high, which do not meet therequirements of current environmental protection.

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