Abstract：Pipeline corrosion prevention is the key factor that affects the reliability and service life of pipeline system，Choose and use reasonable antiseptic coatings，It is of great importance to the safe operation, service life and economic cost reduction of pipelines.
In this paper, the causes of pipeline corrosion, the action of anticorrosive coating and the performance requirements are described,The development of pipeline anticorrosion coating was reviewed,The new development of pipeline anticorrosion coating technology is introduced,The application of these coatings in pipeline corrosion prevention is presented,The development prospect of pipeline antiseptic coating was also prospected.
Keywords:The pipe、corrosion、Anti-corrosion coating、Three-layer polyethylene、Double epoxy
Corrosion is the main cause of material failure，Metal corrosion is a major economic problem，According to relevant data statistics，The annual loss caused by metal corrosion in China accounts for about 5% of the national economy，Among them, pipeline corrosion accounts for a large proportion。With the continuous and rapid development of China's economy，The demand for energy is increasing，Pipeline construction is also increasing，The various kinds of gas supply, water supply and heat supply pipelines to be built in various urban planning are even more numerous，This makes pipeline antiseptic protection more and more important，This is directly related to the pipeline antiseptic performance and operating life。So，It is of great significance to strengthen the research on pipeline corrosion protection coating for the whole pipeline corrosion control。
Two、Research status of pipeline antiseptic coating
2.1Causes of pipeline corrosion
Corrosion refers to the occurrence of chemical and electrochemical effects on the surface and environmental media of metal materials，Cause material degradation and damage。Corrosion of tubing is mainly caused by dissolved CO2, H2S, c1-a small amount of dissolved oxygen and bacteria in crude oil，These substances act directly on metals，Chemical corrosion。
Chemical corrosion is not harmful，As a result, the surface of the steel pipe is convex，The main cause of perforation is electrochemical corrosion。When metals undergo an electrochemical reaction，Where the electrode potential is low, it is easy to lose electrons，As the anode；Where the electrode has high potential,As the cathode。In the case of O2 and H2O，Fe (OH) 2 hydrated iron oxide，That's corrosion。
2.2、Function and performance requirements of antiseptic coatings
1、The function of antiseptic coating
The anti-corrosion principle of the anti-corrosion layer is mainly to prevent corrosive media such as H2O, CL- and SO2 from infiltrating the metal surface of antiseptic coating，So as to prevent metal corrosion。The main function of pipeline antiseptic coating is as follows：1）Shielding effect 2）Corrosion inhibition 3）Sacrificial anode protection 4）Performance improvement
2.3、Development and application of anticorrosive coatings
In 1865，Buried steel pipe when first put into use，There is no solution to the pipeline corrosion problem，Pipeline leaks occur frequently。For leak-proof reasons，Coal tar leaching and modified coal tar enamel are used as antiseptic materials.This material is oxidized when the temperature of the pipe rises,Volatile fraction,Causes brittle and peeling,Increase the cathodic protection current.
The middle of the 20th century was a period of competitive development of various antiseptic materials.Paraffin, petroleum, asphalt and tape have been developed successively,Among them, tape antiseptic layer once occupied the dominant position.But the material is often stripped in corrosive soil,Shielding the cathodic protection current,Results in stress corrosion cracking.
The antiseptic layer of double polyethylene structure appeared in the 1960s,Gradually changed the leading position of coal tar pitch.But with the continuous change of pipeline operating conditions,This kind of antiseptic coating gradually exposed the defects of easy damage, peeling, shielding cathodic protection current and so on.
The Alaska pipeline came into operation in the 1970s,It marked the beginning of the application of dissolved epoxy powder coatings.Through continuous improvement of components and construction procedures,Dissolved epoxy powder became the most successful antiseptic coating in the 1980s,But its mechanical strength is not ideal.
By the late 1990s,Dissolved epoxy powder and three layers of polyethylene two antiseptic coating gradually become the mainstream,In recent years, double layer epoxy has also gradually begun to be applied on a large scale.Currently abroad,There are two distinct views on the choice of antiseptic coatings:North America generally favors the FBE,Europe favours PE.U.S. statistics show that,The present antiseptic layer is the situation of FBE, PE and coal tar,The number and range of other early coatings are increasing and decreasing.
Three、Introduction of three-layer PE and two-layer FBE technology
In the 1980s the German company mannesmann invented a three-layer polyethylene called the "perfect coating"。The manufacturing process is to spray a layer of epoxy primer on the surface of the steel tube，The steel pipe is then fed into the coating zone at a certain rotation speed，The first extruder extruded a film of adhesive according to a certain thickness and density and wound it around the surface of the steel tube，When the adhesive is still melting，The second extruder extrudes polyethylene film and wraps it around the adhesive to form the coating。
The structure of three layers PE antiseptic layer is：The bottom layer is FBE,About 50 to 127 microns，The intermediate layer is copolymer glue，About 200 microns，The outer layer is polyethylene，About 3 mm。This structure will FBE high cohesiveness, oxygen resistance, resistance to chemical corrosion and cathodic disbonding performance and high density polyethylene moisture resistance, electrical insulation and mechanical damage of the resistance combined into an organic whole，It has the advantages of strong adhesion to the pipe surface, good electrical insulation performance, shock resistance and long service life，And the cathodic protection current density is small，Only 1 ~ 3 mu m/m2。
The service life of three-layer PE is expected to reach more than 40 years，But it's more expensive，At present, it is widely used in Europe，It's less used in the United States。Our country has been introduced since 1995，The main steel pipe plants have set up three layers of PE anti-corrosion production lines。A total of about 2000km of shaanxi - jing gas pipeline and ku-shan pipeline use three-layer PE，The coating was also used in the west-east gas pipeline project。
The double epoxy was invented by OBRIEN，It combines the anti-corrosion property of single-layer FBE with the anti-mechanical damage property of surface plastic FBE，It is characterized by strong bond performance, high operating temperature, soil stress resistance, impact resistance and cathodic stripping resistance.The two-layer FBE is composed of two epoxy powders with different properties which are sprayed into a film at one time during the spraying process，The bottom epoxy coating is the same as the single FBE，To provide corrosion protection，The outer FBE is a plasticized epoxy powder layer，Mainly used to resist mechanical damage。The thickness of two layers is usually 525~1000，Suitable for all kinds of caliber pipe，It is also applicable to the antiseptic needs of the joints, elbow and special-shaped components。It is also applicable to the antiseptic needs of the joints, elbow and special-shaped components，Choose a different two-layer FBE structure type。Its shock resistance and cathodic protection current density are similar to those of three-layer PE，It is the only anticorrosion system that can be used in cathodic protection system and is completely compatible without shielding，Failure safety，So much more。
The price of a double FBE varies according to its structure and thickness，But it is generally cheaper than three-layer PE，As the technology matures its cost is still falling。
In our country，Jinshan yiyangzi pipeline, ningbo city gas official website, sinopec material equipment department pipeline and other projects have adopted double-layer FBE。Due to the excellent comprehensive performance and improving economy of double layer FBE,It is bound to be more widely used。
Four、Pipeline anticorrosion coating new technology
4.1Liquid polyurethane anticorrosive paint
Polyurethane asphalt is a pipeline corrosion resistant layer with excellent performance since 1990s，The coating is a two-component thermal spray solvent-free system composed of polyols and isocyanate solutions。This antiseptic coating has superior performance，Simple construction，The antiseptic layer is of good quality，Strong impact resistance and flexibility，Microbiological corrosion resistance，Good scratch resistance, wear resistance and drag resistance，Have some toughness，Good anti - cathode stripping performance，Good chemical stability，Uv radiation，Life is long，Life is long，Cost-effective and environmentally friendly，It has obvious technical and economic advantages，Especially suitable for repairing damage, repairing mouth and old antiseptic layer，At present, it has become the main material for the international pipeline anti-corrosion layer repair，It has a wide range of applications and prospects。
4.2Inorganic nonmetallic antiseptic layer
Compared with organic coatings, inorganic non-metallic coatings have better corrosion resistance, aging resistance, temperature resistance and cold resistance，The service life is greatly improved，There are mainly ceramic coating, enamel coating and glass coating。
Ceramic coatings have high chemical stability，Corrosion, oxidation and high temperature resistance，At present, a variety of ceramic coating methods have been developed, such as self-propagating high temperature synthesis, thermal spraying and chemical reaction。Enamel coating has excellent corrosion resistance and can resist various concentrations of organic and inorganic acids,Various bases and salts,Comprehensive anti-corrosion performance is excellent.The glass coating has good compactness, corrosion resistance and abrasion resistance,A smooth surface,It can reduce drag,Its outstanding characteristic is:Advanced generation technology,Never aging, safe to use, excellent corrosion performance, wear resistance, good mobility, strong weather resistance, non-toxic, harmless pollution, low cost,Construction specifications,Wide range of USES.
Due to the great development prospect of inorganic anticorrosion technology,All countries in the world have taken inorganic non - metal composite anticorrosion pipeline as a key problem,More breakthroughs are expected.
4.3Nano - modified material coating
The research indicated:The organic coating was modified by nano - technology,The comprehensive performance can be improved,Especially increase the mechanical strength, hardness and adhesion of materials,Improve light resistance, aging resistance, weather resistance, etc.By adding some nanoparticles with small particles in the material, the sealing property of the material can be increased to achieve better waterproof and anti-corrosion effect.
For example, nano TiO2 particles have a scattering effect on ultraviolet rays. The addition of such nanomaterials can effectively enhance the anti-ultraviolet ability of the materials and significantly improve the anti-aging property;SiO2 nanoparticles have face serious lack of coordination, large specific surface area and the surface oxygen etc, make its showed strong activity, join the coating can make the coating strength, toughness and ductility increased significantly.For inorganic coating materials, such as nanometer structure, can also improve its plasticity and toughness.
At present, some technologies of modification of anti-corrosion materials by nano technology have been patented, and such anti-corrosion materials have also appeared in the market.In general, however, the technology is still in its infancy and has great prospects for development.
For a long time, the multi-layer composite coatings, such as three-layer PE and double-layer FBE, will occupy the mainstream position of pipeline anti-corrosion coatings.Improving the structure and process of three-layer PE and two-layer FBE, improving performance and reducing cost will also be an important research direction in the future.The liquid polyurethane anticorrosion coating will play an important role in the repair of the pipeline antiseptic coating such as repairing the damage, repairing the mouth and repairing the old antiseptic coating.But as the new material, new craft, new technology application and development of inorganic non-metallic anti-corrosion technology and nanometer technology will have great development and application prospect of pipeline anticorrosion technology will be perfected, pipeline construction will make greater achievement.
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