Lecture on the basics of paint corrosion protection

Corrosion is a natural phenomenon, the material from a high-energy state to a low-energy state of the return, so it is impossible to stop completely. We can only control the corrosion rate by reasonable material selection and taking effective anti-corrosion measures, so that it is within the perilable and controllable range.
1, the usual methods of controlling corrosion include:
(1) reasonable material selection and structural design;
(2) changing the environment (control and treatment of corrosion media, also known as process anti-corrosion measures);
(3) electrochemical protection .
but we don't have three options under any conditions. In more cases, we have no way to change the corrosion environment, nor do we have the conditions for electrochemical protection, structural choices can not fundamentally solve the problem, when reasonable material selection is often the most effective and convenient method.
of anti-corrosion materials is sometimes affected by the characteristics of the material, for example, the manufacture of equipment often requires the use of high strength, good temperature resistance, good mechanical processing performance of metal materials. However, metal materials are often resistant to corrosion and can not meet the requirements, or the price of materials with good overall performance is too high. At this time, people think of a more effective way to cover a more corrosion-resistant material on the surface of the material in need of protection, forming a layer of corrosion protection, using its corrosion resistance and barrier effect to solve the corrosion problem, do not need to spend a higher cost to choose a better comprehensive performance of the material can achieve the purpose of effective corrosion control.
2, anti-corrosion layer on the substrate protection role is mainly reflected in the following three aspects:
(1) isolation: the substrate and corrosion media isolation, to achieve the purpose of corrosion prevention;
(2) Corrosion mitigation: with the help of the internal components of the coating and metal reaction, the formation of a passivation or protective film, improve the protective role of the anti-corrosion layer,
(3) electrochemical protection effect: add active metal materials to the coating, play a role in sacrificing anode protection, reduce corrosion.
3, the use of anti-corrosion layer technology for anti-corrosion methods are as follows:
(1) paint corrosion protection;
4, anti-corrosion layer should have the following properties:

(1) stable chemical resistance
(including good water resistance);
(4) has good bonding and binding force with substrate,
(5) has good anti-cathode peeling and good anti-aging, temperature resistance,
(6) coating should not have adverse effects on the grass-roots materials and contact with the medium, the construction does not cause harm to human body and environment,
(7) has good storage, construction stability,
(8) easy to repair.
Because the paint anti-corrosion has the advantages of simple construction, wide adaptability (suitable for atmospheric, water, general liquid, soil and other environments), easy on-site construction, suitable for large areas and complex equipment, anti-corrosion comprehensive cost is relatively low, short coating period and can achieve better anti-corrosion effect, so it has become the most widely used anti-corrosion technology.
But there are some shortcomings in paint corrosion prevention: thin thickness, mechanical impact resistance is not strong, there are certain life limits, temperature resistance is limited, not applicable to strong corrosion environment.
we are focusing on this today.
5, the classification and characteristics of commonly used anti-corrosion coatings
(1) coating definition and interpretation
definition: applied to the surface of an object can form a protective, decorative or special properties (e.g. insulation, corrosion, logo) solid coating film of a liquid or solid material.
liquid coatings account for the vast majority, solid coatings in recent years is a rapid development of a new type of coatings, with environmental protection, short construction cycle, excellent performance and so on, is expanding the scope of use. Liquid coatings in the field of coatings because of the characteristics of excellent performance, good performance and so on in the field of coatings.
because most of the earliest coatings used were vegetable oils and natural paints as the main raw materials, it is also known as paint. However, with the progress of science and technology, more and more coatings are directly used chemical raw materials synthesis, has been and "oil" without any edge, and many coatings are already water-soluble paint or solid paint, so the word "paint" can not represent the whole paint.
(2) The basic composition of the coating
regardless of the variety and performance of the coating, it is composed of three or four basic components, the effect of which can be seen in the table below:
basic ingredients
typical representative
the main role
the main role of the film-forming substance
(also known as the base material)

vegetable oils (e.g. oil), natural resins, various synthetic resins (e.g. Epoxy resin, polyurethane resin
makes the coating form a complete continuous solid coating film and solid combination with the substrate, is the basis of the coating, determines the basic characteristics of the coating
subsumed medium
volatile organic solvents (e.g. aromatics, esters, ketones), water
so that the film material scattered to form a viscous liquid, helping to improve the paint construction performance and certain characteristics of the coating. Dispersion media itself can not be filmed
pigments and fillers
(body pigments
too white, chrome yellow, chrome green, iron red, talcum powder, calcium sulfate, zinc powder, aluminum powder, etc.
coloring and improve film performance, enhance the protection, decoration and corrosion protection effect of application, but also reduce costs.
Als
drying agent, leveling agent anti-cortifier, curing agent, plasticizer
improve paint production, construction, storage, use characteristics
(3) anti-corrosion coating requirements
(1) to have good adhesion
coating adhesion, especially wet adhesion can replace the water and oxygen on the interface, improve the protective properties of the coating. Therefore, the adhesion of good coatings are generally better anti-corrosion capacity. Stronger adhesion is often required for anti-corrosion coatings used as primers. Therefore, epoxy and alcoholic acid coatings are often used as primers alone.
(2) has strong anti-permeability
strong anti-penetration ability can effectively prevent the penetration of corrosive media. In addition to the innate properties of the coating resin itself, in order to improve the anti-penetration ability, often add mica, iron oxide and other fillers to improve its performance.
(3) Stability of corrosive media
not only requires good stability of coating film-forming substances, but also added additives, fillers, etc. should also be stable, not chemical reactions with the medium or physical changes.
(4) paint classification methods
various types of paint products up to thousands of kinds, classification methods are also many, common classification is:
(1) by whether there are pigments: varnish and paint two categories
(2) by form: water-based paint, solvent-based paint, solid powder coatings, high solid content paint
(3) by use: architectural paint, wood, marine paint, marine paint Drinking water warehouse paint, etc.
(4) according to the construction process: primer, putty, intermediate paint, paint, hood paint
(5) according to the effect of use: insulation paint, anti-rust paint, anti-fouling paint, anti-corrosion paint, fire paint
(6) according to the paint main film material sub-components: natural resin paint, asphalt paint, phenolic paint, oxygen paint, polyurethane paint...
(5) The performance characteristics, use and selection principles of commonly used anti-corrosion coatings
Anti-corrosion coatings are not the same because the main film-forming substances have different anti-corrosion properties, applicable conditions, construction characteristics, service life and price level. Therefore, the characteristics of various coatings should be understood before the selection of coatings. The following table is commonly used synthetic resin coating characteristics and main uses:
main film-forming substances
film characteristics
main uses
olic acid resin
bright, weather-resistant, strong adhesion, but soft texture, water resistance, alkali resistance Poor sex
construction, vehicles, machinery, ships, light industrial products
aminate resin
bright, good color preservation, hard, but the need for thermo-curing
defons, machinery, machinery products
chlorinated vinyl resin
weather-resistant, corrosion-resistant, water-resistant, oil-resistant, anti-combustion, but poor adhesion, temperature resistance, low solid components, thin film thickness
chemical equipment
vinyl resin
light color, good flexibility, corrosion resistance, but solid group Low score, thin film thickness
cement, chemical equipment
acrylic resin
bright, light color, good color preservation, strong weather resistance
construction cars, machinery, light industrial products
polyester
flexible, wear-resistant, construction trouble
wood
epoxy resin
tough, wear-resistant, excellent adhesion, corrosion resistance, single color depth, poor weather resistance
chemical equipment
polyurethane
meninges, corrosion resistance, good insulation
aircraft, ships, chemical equipment, wood Device
silicone resin
weather resistance, high temperature resistance, good insulation, but poor adhesion, gasoline resistance, more brittle
coated electrical materials, heat-resistant equipment
organic polymer
high temperature, fire resistance
ships, bridges
each coating with different performance characteristics of its applicable environment is not the same. The following table makes the recommended table for coatings in some common corrosion environments in the petrochemical industry.
corrosion media environment
recommended preferred paint varieties
recommended thickness (sm)
field application examples
General atmosphere
phenol resin coatings, asphalt coatings, aolic acid resin coatings
≥
120 power plant boiler room, oil refining space, fertilizer boiler room, other dry indoor environment equipment
chemical atmosphere
asphalt coatings, perchloroethylene coatings, vinyl resin coatings, epoxy resin coatings, polyurethane coatings, polyurethane coatings Ester coatings, inorganic zinc-rich coatings, chlorine polyethylene coatings, chlorinated rubber coatings, perchlorinated polyethylene
≥150
refining, fertilizer, chemical fiber, chemical plant production plants
acid gas, acid mist
perchloroethylene coatings, vinyl resin coatings, epoxy coatings (only for primers and intermediate paints), chlorine polyethylene coatings, chlorinated rubber coatings, polyurethanes, special cyanide
≥200
chemical fiber oxidation, Chemical plant melamine, power plant water
al alkaline environment
perchloroethylene coating, vinyl resin coating, epoxy resin coating, silicone coating, chlorine polyethylene coating, chlorinated rubber coating,
≥150
Fertilizer synthesis, fertilizer urea
acidic, alkali, salt sewage environment
phenolic resin coatings, perchloroethylene coatings, vinyl resin coatings, epoxy resin coatings, polyurethane coatings, inorganic zinc-rich coatings, chlorine-sulfurized polyethylene coatings, Chlorinated rubber coatings, special cyanide
≥250
refining sewage
oil-resistant coatings
epoxy resin coatings, polyurethane coatings (for the inner wall of refined oil storage tanks must be used electrostation varieties
≥25 0
The inner wall of the refinery oil storage tank
water-resistant, moisture-resistant coatings
phenolic resin coatings, asphalt coatings, perchloroethylene coatings, vinyl resin coatings, epoxy resin coatings, polyurethane coatings (including special cyanide), Chlorinated polyethylene coatings, chlorinated rubber coatings, SBS waterproof coils (for roofing), chlorinated polyethylene waterproof coils (for roofing)
chlorinated polyethylene, epoxy, polyurethane, phenolic coatings ≥200≥;
cycle water field, cooling tower, pool, factory floor
temperature-resistant coatings
≤ 100 degrees C: phenolic resin coatings, aortic resin coatings, epoxy resin coatings, polyurethane coatings, inorganic zinc-rich coatings
≥120
All kinds of equipment, pipes
100 degrees C to 200 degrees C: epoxy resin coatings, inorganic zinc-rich coatings
≥120
heating furnaces, equipment, flue gas pipes, chimneys
200 degrees C or more: organic Silicon coatings
≥60
gasifiers, high temperature reactors, regenerators
water cooler special coatings
TH847, DH22, JST-2L heat exchanger special coatings
110 to 160

the plant carbon steel water cooler tube bundle
buried pipe
asphalt glass cloth, coal tar asphalt glass cloth, epoxy coal asphalt glass cloth, polyethylene thin tape, epoxy powder coating
2 to 7mm
All kinds of buried pipelines
the selection of anti-corrosion coatings must consider the use of environment and construction conditions. For example: in the buried pipe corrosion prevention should be preferred to choose water-resistant asphalt coatings, in the heavy corrosion environment should be selected in high viscosity, disposable film thickness of anti-corrosion coatings, perchloroethylene, nitro paint and other volatile fast-drying paint is not suitable for spraying construction, chlorine polyethylene is not suitable for rolling back and forth method construction.
the selection of anti-corrosion coatings should also take into account the matching nature of the coating, primers and substrates should have good compatible, primers and finishes can not occur between the phenomenon of mutual solubility, biting. For example: chlorine-sulfurized polyethylene on concrete surfaces can be used as a primer or as a finish, but is not suitable for primers on steel surfaces; epoxy tree coatings can be used as primers in most cases, but are not suitable for painting in open environments because epoxy coatings are less resistant to ultraviolet light;
varieties of coatings should also take into account the comprehensive economic factors. Sometimes the price of paint is low but the life is short