Where is the future from the application technology of marine anti-corrosion coatings?

Lead

In recent years, more and more attention has been paid to marine corrosion and protection at home and abroad, although various seawater corrosion resistant materials have been continuously introduced, and various anti-corrosion construction technologies have also developed greatly, but they are still far from meeting the actual needs
.
There is a clear gap between China's anti-corrosion research on marine engineering structures and facilities and foreign developed countries, some key technologies have not yet been solved, no technology with independent intellectual property rights has been formed, and the lack of corresponding anti-corrosion norms and standards, which have seriously affected the design, construction and safe operation of
marine engineering structures.

Therefore, in view of the common and key anti-corrosion problems faced by China's key sea areas and major marine projects, the research on the key technology of long-term anti-corrosion of marine engineering structural facilities can not only prevent the occurrence of corrosion, avoid or reduce the repair, maintenance costs and economic losses caused by maintenance in the later service, reduce the occurrence of major malignant accidents, but also greatly improve the safety of offshore engineering facilities, which is of great significance to the online coatingol.
com
of coatings.

Requirements for marine anticorrosive coatings

Marine anti-corrosion coatings refer to anti-corrosion coatings
used in marine environments.
Because the marine environment is very harsh and highly corrosive, marine corrosion prevention is a topic
that urgently needs to be seriously studied in the development of marine engineering in China.

According to the material and corrosion mechanism of anti-corrosion objects, marine anti-corrosion coatings can be divided into marine steel structure anti-corrosion coatings and non-steel structure anti-corrosion coatings
.
Marine steel structure anti-corrosion coating mainly refers to the anti-corrosion coating of large facilities such as transportation ships, containers, offshore bridges, port machinery, oil pipelines, offshore oil production platforms, etc.
, and non-steel structure marine anti-corrosion coating mainly refers to the anti-corrosion coating
of marine concrete structures.
Marine anti-corrosion coatings mainly include inorganic zinc-rich, organic zinc-rich, silicone, epoxy, acrylic, polyurethane, fluorocarbon, polysiloxane coatings, according to different marine environment corrosion characteristics and anti-corrosion years to choose different coatings and coating systems
.

Marine anticorrosive coatings are generally required to have the following properties:

(1) It has good physical properties
.
Good impermeability to corrosive media and good adhesion to steel surface;

(2) It has good mechanical properties
.
Resistant to seawater erosion, sea ice collision, and wear and tear of ship docking;

(3) Excellent chemical properties
.
Resistant to seawater, salt spray, oil, chemicals, ultraviolet rays, etc.
;

(4) Good
compatibility with electrochemical protection systems.
Splash zone and full immersion zone coatings should be resistant to cathodic peeling;

(5) It has good construction performance
.
High-quality coating of different structures under various environmental conditions;

(6) Meet the requirements of
health, environmental protection and safety.
The coating is required to have high solid content and volatile organic compound (VOC) content to meet the requirements of national or international standards;

(7) Other special requirements
.
Such as: freshwater tank coatings are required to be non-toxic and meet the requirements of national health certification; The filterable chlorine removal content in the coating used on the surface of stainless steel cannot exceed 200mg/kg, and the coating does not contain zinc; Ship ballast tank coatings should meet the requirements of the International Maritime Bureau (IMO) "Performance Standards for Protective Coatings for Ship Ballast Tanks"; Coatings below the waterline of ships are required to prevent the adhesion of marine organisms
.

Marine heavy anti-corrosion coating standard

The main relevant international standards of commonly used marine heavy anti-corrosion coatings are:

(1) ISO 12944 "Corrosion Protection of Steel Structures by Protective Coating Systems" (2) NORSOK M501 "Surface Treatment and Protective Coatings" (3) ISO 20340 "Performance Requirements for Protective Coating Systems for Offshore and Related Structures" (4) NACE SP0108 "Corrosion Control of Offshore Structures by Protective Coatings" (5) IMO Performance Standard for Protective Coatings for Ship Ballast Tanks (PSPC)

Marine anticorrosive coatings and their coatings typically meet the requirements
of ISO 12944, NORSOK M501, NACE SP0108 and ISO 20340 related anti-corrosion standards.
Generally, it is necessary to pass strict corrosion tests and certifications in advance, and the test items mainly include:

(1) Salt spray (salt water) resistance test for 4000 hours; (2) Cathodic peel resistance test; (3) Damp heat resistance test for 4000 hours;

(4) Cyclic corrosion test 4200 hours
.
Marine anticorrosive coating research and development key marine anticorrosive coatings research and development has high scientific and technological content, long development cycle, large investment, high technical difficulty and high risk, foreign marine anticorrosive coatings research and development is mainly concentrated in strong large companies or relying on government support departments
。 For example, the British IP, the United States PPG, Denmark's Hemple, Norway's Jotun and Japan's Kansai paint and other large companies have hundreds of years of related paint development history, in the coating production and supply, quality supervision, coating specifications and coating site management and other aspects of the formation of a set of very strict and strict system, at present these companies' products occupy China's marine anti-corrosion coatings main market
.

The production of marine anti-corrosion coatings in China is mainly concentrated in Qingdao, Shanghai, Dalian, Tianjin, Changzhou, Guangzhou and Xiamen and other coating enterprises, and the research work is mainly concentrated in the Institute of Oceanography of the Chinese Academy of Sciences, the Institute of Metal Corrosion of the Chinese Academy of Sciences, the Institute of Marine Chemical Industry, CNOOC Changzhou Coatings Research Institute, CSSC 725 and other research institutions
.
In recent years, although quality management and supervision institutions such as "China Shipbuilding Industry Xiamen Testing 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 anti-corrosion coatings mainly focus on the following aspects
.

Long life

Because more and more super-large steel structures and the characteristics of the sea area do not have the conditions for direct recoating or back-to-shore construction, it is required to develop marine anti-corrosion coatings with a long service life, and the ideal coating service life includes the extended service life after direct painting and maintenance on site is equivalent to the service life of steel structure equipment, that is, the coating is designed with the same life as the equipment, and only a small amount of maintenance is required in use, free from recoating
。 Belgian coated zinc coating belongs to organic high-zinc rich coating, the metal zinc content in the dry film is 96%, in the coastal marine atmosphere environment of Oslo, Norway, the average annual coating loss measured after 15 years of coating with a film thickness of 120μm on the steel bridge is only 1μm
.

The most typical successful case of inorganic zinc-rich coating application is the 250km long tubing project in Morganwyalla, Australia, which adopts a single-layer waterborne inorganic zinc-rich coating for corrosion protection, and the coating has remained in good condition for more than 50 years without corrosion
.
The refinery built by Exxon in the United States uses a single-layer zinc silicate anti-corrosion coating, which needs only a small part of the coating to repair after 15 years, and then remains rust-free for 4 years
.

As a topcoat, the weather resistance of fluorocarbon coatings and polysiloxane coatings developed has reached more than 15 years, such as CFFE fluorocarbon paint produced by Asahi Nitrate subsidiary in Japan, tetrafluoroethylene FEVE fluorocarbon paint produced by Daikin Company, acrylic polysiloxane coating interfine979 produced by International Paint Company and epoxy polysiloxane coating PSX700 produced by AMERON Company of
the United States.

Low surface treatment

Since the cost of pre-coating 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 coatings that can be rusted and wet painted, as well as coatings
that can be applied directly to the surface of other kinds of old coatings.
This kind of coating is mainly epoxy, they have the function of direct coating on the surface of wet rusty steel, have super adhesion, VOC content < 340g/L, a gasless spraying film thickness can reach more than 200μm, excellent<b11> construction performance.
Pre-installation treatment costs will account for 60% of the total coating cost, so low surface treatment coatings have become one of the important research directions of
anti-corrosion coatings.

High solids, solvent-free

Coatings with a volumetric solid content of more than 70% are high solids coatings, and solvent-free coatings
with a solid content of 100%.
Because less or no organic solvents are used, the high solids coating can reduce VOC emissions, meet environmental protection requirements, and obtain the required film thickness in one application, thus reducing the number of construction passes, saving recoating time and improving work efficiency
.
Due to solvent-free volatilization, the porosity of the coating is reduced, which improves the impermeability and corrosion resistance of the coating
.

Water-based

Coating hydration is another important aspect of
coatings development.
Its low VOC content is of great significance
for energy conservation and emission reduction, the development of low-carbon economy, environmental protection and sustainable development.
At present, the research and development of water-based coatings is mainly in the fields of
waterborne inorganic zinc-rich, water-based epoxy, water-based acrylic acid, and water-based fluorocarbon systems.
Among them, the industrial application of waterborne acrylic, waterborne epoxy and waterborne inorganic zinc-rich coating varieties has been successful
to a certain extent.
Asahi Nitrate has developed a new low-VOC waterborne FEVE copolymer, which is comparable to solvent-based fluorocarbon paint in terms of weather resistance, water resistance, solvent resistance and gloss of the prepared
coatings.

In March 2008, at a corrosion protection seminar organized by the American Society of Corrosion Engineers (NACE), Hydro Oil Energy of Norway tested and evaluated waterborne coatings according to NORSKOKM-501, and the results showed that waterborne coatings have encouraging prospects
for coating and repairing new facilities in ocean-going environments.

In March 2008, at a corrosion protection seminar organized by the American Society of Corrosion Engineers (NACE), Hydro Oil Energy of Norway tested and evaluated waterborne coatings according to NORSKOKM-501, and the results showed that waterborne coatings have encouraging prospects
for coating and repairing new facilities in ocean-going environments.

New environmentally friendly materials

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

The U.
S.
Department of Energy's Brocavin Laboratory has developed a bio-heavy anti-corrosion coating using grain, crab shell and lobster shell as raw materials, which becomes strong and smooth under the right temperature conditions, and can adhere tightly to aluminum or other metal surfaces to prevent metal corrosion
.

Polyurea elastomers

Polyurea coating is a solvent-free, pollution-free high-performance heavy anti-corrosion coating, referred to as SPUA
, which has emerged in recent years.
SPUA is two-component, 100% solid content, environmentally friendly, its curing speed is fast, insensitive to humidity and temperature, and is not affected by ambient humidity during construction; After curing, the coating film has excellent elasticity and strength, weather resistance and thermal stability, no cracking and no falling off for long-term outdoor use, good adhesion to steel, and excellent corrosion resistance
.
However, SPUA has extremely strict requirements for the surface treatment of the substrate to be coated, and the steel must be thoroughly sandblasted and coated immediately after treatment
.

The United States and Taiwan have applied it in the corrosion prevention of offshore structures, especially the coating of offshore platform steel structures in the splash zone
.
Polyureas mainly include aromatic polyureas, aliphatic polyureas and polyaspartate aliphatic polyureas
.

Marine anticorrosive coating analysis and recommendation

Coating application status and problems

At present, most of the anti-corrosion coatings used in marine engineering are products of foreign multinational company brands, and there are few
domestic coating products.
Whether in the quality of coating products or its quality control mechanism, there is a big gap
between domestic coating products and foreign products.
The reason is mainly due to the short development time of marine anti-corrosion coatings in China, the lack of core technology, the lack of research funds, and the low level of researchers, which greatly restrict the entry of domestic coatings into the international offshore market and weaken the competitiveness
of domestic brands.

Based on the use environment of offshore products, anti-corrosion protection measures must be taken, for offshore marine product anti-corrosion coatings, it is difficult to repair or repaint at sea during the service period, extending the durability of anti-corrosion coatings and synchronizing the service life of anti-corrosion coatings and offshore products is the ultimate goal
of offshore anti-corrosion research 。 Therefore, the research and development of marine heavy anti-corrosion coatings and coating technologies with more than 15 years of durability in the marine environment, the design of metal coating + organic coating supporting system and multi-layer organic or inorganic coating supporting system that can reach 15~30 years of durability in the marine environment, is the focus of the national marine development strategy marine corrosion prevention needs to be studied, and the development of a primer with high cathodic protection efficiency, a medium coating with good shielding effect and a topcoat with good weather resistance, And the suitable coating matching design is the technical key
to the anti-corrosion coating supporting system.

Marine anti-corrosion coatings are currently mainly used to prevent corrosion of structures exposed to the marine atmosphere, and underwater parts of offshore structures (such as ships and drilling platforms) immersed in seawater, especially in deep water areas, seabed steel pipes, etc.
also need to use coatings to prevent corrosion
.
Due to the low oxygen content and relatively low corrosion degree in this area, epoxy coatings, epoxy asphalt coatings, epoxy glass flake coatings, etc.
are mainly used, and if you need to prevent the adhesion of marine organisms, the combination system
of epoxy coating + antifouling coating is used.
For the seabed zone, the coating is mainly epoxy asphalt coating
due to the lowest degree of corrosion in this area.
In addition to liquid epoxy coatings, steel pipelines also use a large number of molten epoxy powder coatings, which are usually required to be used normally for more than
20 years without maintenance due to the extremely difficult maintenance.

Anticorrosive coatings used in seawater are usually required to have good resistance to marine organisms and chemical stability to ensure that the coating can prevent fouling and corrosion; It has good mechanical strength to ensure that the coating can withstand certain pressure and collision, and maintain the integrity of the coating so that it does not crack or fall off; There should be good adhesion to the surface of the steel pipe and the 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 are currently the main methods
of marine anti-corrosion.
Compared with the anti-corrosion performance of the coating, the application performance and repairability of the coating in seawater are more important, so it is usually recommended that the coating life be the same as the main body of the coated structure or can be maintenance-free
.
In addition, the use of anti-corrosion coatings that can be applied in water is also the direction of current development, and many foreign companies have developed such products, which are usually liquid high solids epoxy coatings
.

Shipbuilding is an industry that uses marine anti-corrosion coatings more in marine engineering, and China's ship anti-corrosion coating coating technology that is closely related to this has also achieved rapid development and reached a certain level, such as the coating process has been listed as one of the important contents of ship design; The steel pretreatment process has been widely used in shipbuilding enterprises, and a segmented rust removal and spraying workshop has been established, and equipped with corresponding automatic and semi-automatic rust removal and spraying equipment, and a series of technical standards for rust removal and coating have been formulated; Practitioners have mastered high-performance coating application processes and special coating technologies 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 China's coating technology level, production efficiency and coating quality, significantly shortened the gap with foreign coating technology, and the coating quality has been praised
by domestic and foreign shipowners.
However, there is still a big gap between China's ship coating technology and foreign countries, which is mainly manifested in the following aspects:

(1) The depth of ship coating production design is not enough, and the concept of shell outfitting integration is not strong;

(2) The degree of mechanization and automation of ship painting technology and equipment is not high, resulting in more rust removal and high coating indicators;

(3) The pretreatment quality and workshop primer performance need to be improved;

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

Problem-solving ideas

Marine engineering corrosion prevention involves the national marine development strategy, so it is hoped that relevant national departments or industry organizations can take the lead in organizing relevant and integrating social resources at the national level, carry out collaborative research on the key problems that need to be solved in marine anti-corrosion coatings and coating technology, and provide strong financial support
.

It is recommended that research work be strengthened in the following areas:

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

(2) Strengthen the research of
paint coating process.
Starting from the integration of coating coating, we attach importance to the research of coating construction performance, continuously optimize and improve the comprehensive performance of coating products, develop coatings with good construction performance and strong adaptability, and improve the scientificity and rationality of supporting coating systems to adapt to the different coating requirements
of different offshore products.
Usually the integration of coating is implemented by a third party, that is, the offshore construction company outsources all its coating production to a professional coating engineering enterprise - a third party, which is only responsible for supervision and inspection
。 At present, some powerful coating companies and coating equipment companies have launched the BOT service model, that is, the coating workshop of the offshore builder is invested and constructed by the coating company or the coating equipment company, and is responsible for production management, according to the production plan of the offshore builder for coating production, to achieve the integration of coating coating, and finally provide qualified coatings instead of liquid or powder coatings, and offshore builders only need to formulate technical standards and acceptance to supervise the quality of coating products, according to the coating quality and coating area
。 This model will become the development trend
of coating integration.

(3) Improve the anti-corrosion performance and construction performance of marine anti-corrosion coatings, strengthen the development of workshop primers with high temperature ablation resistance (>800 °C), solvent-free anti-corrosion coatings with high solid content, low viscosity characteristics and convenient construction, self-drying or low-temperature drying water-based inorganic zinc-rich primers, water-based acrylic, epoxy anti-corrosion coatings and epoxy thick slurry coatings that can be coated at one time with 300~500μm, and heavy anti-corrosion coatings that can be coated underwater, One-component zinc-rich primers and moisture-curing polyurethane anti-corrosion coatings with better corrosion resistance, inorganic or inorganic modified anti-corrosion coatings with better anti-corrosion performance and aging resistance, etc
.

(4) Most of the offshore structures are large in size, most of the current coating construction is carried out in the open air, manual spraying is the main coating method, coating efficiency is low, quality is difficult to guarantee, so mechanized coating is the main direction
of its development.
For port machinery, platforms, special ships and other offshore engineering products with a large number of pipe fittings, rods, section steel, box girder with standardized shape, shot blasting and coating mechanized production lines can be used to carry out coating, which can greatly improve production efficiency, ensure coating quality, shorten the construction period and protect the environment
.
For relatively simple appearance and large number of supporting parts, online robot coating or electrostatic spraying can be used
.
For manual brushing and roller coating with low coating efficiency, paint brushes or paint rollers that can automatically supply paint should be developed to improve efficiency, and similar products
have been made abroad.

(5) Strengthen the training of
professional personnel.
In the final analysis, market competition is the competition of talents and the competition of management level, and the weakest link in China's national defense corrosion coating and coating enterprises compared with similar foreign enterprises lies in this
.
At present, most of the personnel engaged in coating technology are converted from chemical engineering or mechanical engineering, due to professional setting reasons, there are few personnel specializing in metal corrosion protection, so there are many people who know it, few people know it, and there is a lack of engineering researchers
who can not only conduct coating anti-corrosion research but also be proficient in coating construction technology.
There are only a few colleges and universities in China that cultivate metal anti-corrosion professionals, which cannot meet the needs of the industry, and it is necessary to expand the scale of
talent training.
At the same time, the coating construction personnel are the ultimate implementers of the coating process, and their technical quality will directly affect the coating quality and even the anti-corrosion performance
of the coating film.
At present, most of the personnel in the frontline coating construction are migrant workers without professional training, and there is a lack of professional knowledge, so training qualified coating workers, especially spray operators, is also an urgent problem
to be solved in the painting industry.
Systematic social and internal professional education is recommended, such as training according to the syllabus for painters, to bring them to intermediate or advanced paint wage levels
.
In addition, the implementation of certificate is also one of the important ways to improve the quality of construction personnel and the quality of
painting.

(6) Coating inspection is the final link to ensure the quality of coating, and it is also a very important link, which must be carried out
by professionally qualified inspectors.
Usually offshore products and international standards require that the personnel who carry out coating inspection must be trained by NACE, SSPC, FROSIO coating inspection and obtain the corresponding professional qualifications, and need to reach the second or third level to carry out this work
.
China should introduce relevant foreign training and teaching materials in this link, train full-time coating inspectors in accordance with foreign standards, implement the coating inspection qualification certification system in marine anti-corrosion coating projects, improve the level of domestic coating inspection, and improve the coating quality
of marine engineering.