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. Global Coatings Network understands that marine anticorrosive coatings mainly include inorganic zinc-rich, organic zinc-rich, silicone, epoxy, acrylic, polyurethane, fluorocarbon, and silicone coatings, which can be selected according to different marine environmental corrosion characteristics and corrosion protection years. Coatings and coating systems.
Marine anticorrosive coatings generally require the following properties:
1 has good physical properties. It has good impermeability to corrosive medium and good adhesion to steel surface; 2 has good mechanical properties. It is resistant to sea water scour, sea ice collision, and ship-resistant wear; 3 has excellent chemical properties. Resistance to seawater, salt spray, oil, chemical, UV, etc. 4 Compatibility with electrochemical protection systems. Splash zone and full immersion zone paint should have cathodic disbonding resistance; 5 has good construction performance. High-quality painting and construction can be carried out on different structures under various environmental conditions; 6 meet the requirements of health, environmental protection and safety. The coatings are required to have a high solid content and the volatile organic compound (VOC) content meets the requirements of 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 200mg/kg, and the coating does not contain zinc; the ship's ballast tank coating should conform to international maritime affairs. Bureau (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 anti-corrosion coatings are: 1ISO12944 protective coating system for corrosion protection of steel structure; 2NORSOKM501 surface treatment and protective coating; 3ISO20340 offshore and related structural protective coating system performance requirements; 4NACESPO108 protective coating for offshore structure Corrosion Control; 5IMO Ship Ballast Tank Protective Coating Performance Standard (PSPC).
Marine anti-corrosion coatings and their coatings are usually required to meet the requirements of ISO12944, NORSOKM501, NACESPO108 and ISO20340 related corrosion protection standards. Generally, it must pass strict corrosion test and certification in advance. The test items mainly include: 1 salt spray resistance (brine salt) test 4000h; 2 cathodic resistance peel test; 3 heat and humidity resistance test 4000h; 4 cycle corrosion test 4200h [1-4].
2. Marine anti-corrosion coating research and development focus
The research and development of marine anti-corrosion coatings 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 [5].
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
As more and more super-large steel structures and the characteristics of the sea area do not have the conditions of direct recoating or back-to-shore construction, it is required to develop marine anti-corrosion coatings with long service life. Ideally, the coating service life includes direct on-site operation. The continuation service life after 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 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 15a coated on a steel bridge with a film thickness of 120 μm After the actual measurement, the average coating loss per year is only 1 μm [6].
The most typical successful application of inorganic zinc-rich coatings is the 250km 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 15a, only a small part of the coating is needed to be repaired. After the replenishment, it is completely rust-free after 4a.
For topcoats, the weather resistance of currently developed fluorocarbon coatings and silicone coatings can reach more than 15a, such as chlorotrifluoroethylene FEVE fluorocarbon paint produced by Asahi Glass Co., Ltd., and tetrafluoroethylene FEVE fluorocarbon produced by Daikin. Acrylic polysiloxane coating interfine979 produced by lacquer and international paint company, and epoxy polysiloxane coating PSX700 produced by American Ameron Company.
2.2 low surface treatment
Since the pre-painting treatment cost accounts for 60% of the total coating cost, low surface treatment coatings have become one of the important research directions of anti-corrosion coatings.
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