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    Home > Coatings News > Paints and Coatings Market > Paint and coating for petrochemical industry: anticorrosive coating system for the inner wall of crude oil tank

    Paint and coating for petrochemical industry: anticorrosive coating system for the inner wall of crude oil tank

    • Last Update: 2021-01-14
    • Source: Internet
    • Author: User
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    China Paint Online News: How much paint does
    100,000 cubic meters of crude oil storage tank to use?
    as the world's largest crude oil importer and second consumer, China's crude oil storage tank will naturally not be less, and will continue to build new tanks. Let's talk about the selection of anti-corrosion coatings for each part of the inner wall of the crude oil tank. Interested friends can leave a message at the end of the article to participate in the discussion.
    Most of the tanks are now in the installation molding, and test water pressure, before surface treatment and painting, although the 100,000 cubic meters of the tank is very large, but after the float installation of the internal basic closed, only around the tank left a few holes for access, dark, damp, closed is the environment inside the tank, I went in many times, it is like a coffin feel very dark, after you go in to ensure that you immediately think out. In addition, today's anti-corrosion coating team is mostly connected to the construction team of qualified companies, all kinds of equipment (such as explosion-proof lighting, ventilation and cleaning equipment in tanks) are sometimes not adequately equipped. Under such environmental conditions, the difficulty of doing a good job of surface treatment and coating is predictable.
    Usually we choose anti-corrosion coating system, to consider a number of factors, including: substrate type and surface treatment, corrosion environment, coating environmental conditions (ventilation, temperature, humidity, etc.), feasible construction methods, etc. , the more factors to consider, in order to ensure that the site can be expected to construct a high-quality anti-corrosion coating.
    Below we talk about the selection of anti-corrosion coating system in various parts of the inner wall of the tank:
    1, the surface of the tank floor and the inner wall of the tank under the oil and water line
    This is the most serious corrosion of the crude oil tank, is the key area of anti-corrosion of the tank, corrosion prevention is not done well, corrosion perforation will occur. The GB50393-2008 provides for an insulated corrosion-resistant coating with a surface resistivity of not less than 300 m (surface resistivity of not less than 1013 s). On behalf of another opinion, "China Coatings Industry Association industry norms CNCIA-HG/T0001-2006 "oil storage tank conductive electrostitive anti-corrosion coating and acceptance specifications" that the coating thickness should be used not less than 400 microns of insulation anti-corrosion coating (surface resistivity is not less than 1010ω), it is clear that the two views are similar. However, since the surface resistivity of most insulated corrosion-resistant coatings is not less than 1013 s, coating some of the film thickness is of course more conducive to corrosion prevention, so that the differences between the two factions here is not important.
    I have read a lot of crude oil storage tank anti-corrosion specifications, most of which are regular large-scale petrochemical design institute products, and some are local design institutes or private design institutes, basically more or less by reference to GB50393-2008 requirements for design. The coating system is generally designed as follows:
    A, epoxy zinc-rich primer, epoxy intermediate paint, epoxy paint
    B, epoxy primer, epoxy intermediate paint, epoxy paint
    C, epoxy glass scale coating (base, Medium and surface)
    D, solvent-free liquid epoxy coating
    I personally prefer to recommend solvent-free epoxy, for the following reasons:
    (1), the previous introduction, the tank is basically closed, poor ventilation, the use of solvent-free epoxy is relatively safe. It can avoid the occurrence of flash explosions similar to those in the coating operation of the Dushanzi crude oil tank.
    (2), solvent-free epoxy thick coating is good, reduce the number of construction channels and time, roller coating two to reach 400-600 microns is very easy. Working in this environment, everyone wants the shorter the better.
    (3), there is also a point, because the bottom of the tank is horizontal, painters sometimes when the construction is to pour the paint up, and then with the rollers to smooth things, you set 3 5 lanes, they may be finished as soon as they fall. In fact, the coating film is too thick, and it is a single construction. For solvent-based coatings (even if high solids), solvents are difficult to volatile, the consequences of a single construction too thick, paint people can expect. There will be solvent residues, which will cause the coating to crack due to shrinking stress, which in turn will start to layer and shell. The solvent-free epoxy shrinkage is much lower and no solvent needs to be volatile.
    , to remind designers, paint suppliers and other relevant parties. If the design is multi-channel coating, be sure to choose each layer of color is different (such as red, gray phase), supervision and field service representatives must be on-site watching, otherwise there will be a fall phenomenon. I have also been asked the reason for cracking, they suspect that because the flexibility of the coating (bend resistance) is not good, the bottom plate with the oil load changes will have a certain scratch deformation, this flex deformation caused the coating cracking. I don't think it's for that reason at all. Because the curvature diameter of this flexing deformation of the tank bottom plate is certainly measured in meters, the anti-bending resistance of the coating is no worse, and the test of anti-bending resistance is also measured by mm.
    interested friends may read another of my articles:
    Solvent-free epoxy coating applications in tanks and pipes
    And one more thing I don't think is appropriate for zinc-rich primers, for the following reasons:
    Given the chemical vibrancy of zinc When used in water, acid or alkali, salt, sulphides and other impurities easy to deposit oil and water lines below the tank wall and above the surface of the tank floor, will lead to the rapid consumption of zinc powder and the occurrence of hydrogen corrosion, hydrogen corrosion will also lead to coating foaming.
    theory that zinc may reverse polarity when it is greater than 54 degrees C and has media such as acid and alkali, thus losing cathode protection. Will it happen in some insosted crude oil storage tanks?
    Since the zinc-rich primer film is a coating with conductivity and cathode protection, is there a duplication of cathode protection when the coating is used in conjunction with anode protection, using zinc-rich corrosion-resistant coatings? Will it affect the number and rate of consumption of sacrificing anodes?
    2, the surface under the floating disk and the side wall of the floating disk
    In GB50393-2008, an oil-resistant conductive electrostecturic coating (surface resistivity of 108 s-1011 s) is specified in no less than 250 m. On behalf of another group of views, "China Coating Industry Association industry norms CNCIA-HG/T0001-2006 "Oil storage tank conductive electrostitive anti-corrosion coating coating and acceptance specifications" that the coating thickness should be used not less than 350 microns of oil-resistant conductive electrostectrical coating (surface resistivity 105 s-109 s), obviously the two opinions of the urgent discussion reflected in the coating thickness and surface resistivity. The selection of coating varieties is consistent.
    considering that this part is always immersed directly in the upper oil, since corrosive media such as water are usually deposited at the bottom of the tank, the oil corrosion here is light. The coating thickness of 250 m should be sufficient. When coating work in the tank, the top roller brush is very labory (now for safety reasons, the tank is basically not sprayed construction). Now the design is basically a high solid part of epoxy oil-resistant conductive electrostectantic coating, but also designed to use solvent-free epoxy conductive electrostectrical coating.
    The most common coating defect here is inter-layer peeling for the following reasons: When the humidity in the
    tank is high, the surface of this area is prone to condensation, affecting the adhesion between the coating and the substrate and each coating.
    -resistant coatings are usually high cross-link density thermostats, there must be the longest coating interval limit, more than the maximum coating interval construction without polishing, inter-layer adhesion is difficult to ensure.
    people believe that the use of solvent-free epoxy conductive electrostation coating is more conducive to safety, if the use of high-pressure airless spraying a construction, it will not lead to inter-layer adhesion problems.
    3, the interior surface of the pontoon
    may be due to the pontoon interior surface corrosion is very light, the relevant standards are not mentioned here.
    But according to some examples of tank construction, there are the following coatings commonly used in this area:
    1, epoxy coal asphalt anti-corrosion coating, in the early tank construction is more commonly used;
    2, epoxy primer and epoxy. Usually the same as the epoxy primer and medium paint used on the outside wall of the tank;
    3, water-based inorganic zinc-rich primer
    4, water-based epoxy anti-corrosion coating
    5, solvent-free epoxy anti-corrosion coating
    coating thickness is usually 100-200 microns.
    are now usually soldered before the first coating plate, molding installation and then drill into the repair. Patching paint, I think the most suitable or solvent-free epoxy, the reason is not it, closed environment.
    A better understanding of this part, you can see another article I wrote, "Water-based epoxy anti-corrosion coating in the floating roof tank floating tank surface corrosion protection application discussion", however, this article has not yet been issued in this public number, will be issued in a few days.
    4, insulation tank heating tube
    the tube inside the steam is about 180 degrees Celsius, and the temperature of the oil usually does not exceed 90 degrees Celsius, so the temperature of the outer surface of the tube is estimated at 90-150 degrees Celsius. The key is that this coating is resistant to long-term immersion of hot oil. The coatings now designed are typically:
    silicone heat-resistant paint
    epoxy modified silicone heat-resistant paint
    organic zinc-rich primer
    coating thickness of 150-200 microns.
    I think that silicone heat-resistant paint cross-link density is not high, oil resistance is certainly not as good as the 2nd; zinc-rich primer, mentioned above does not recommend the reasons;
    5, the middle part of the inner wall of the tank
    This part was previously coated with oil-resistant electrostectrecturation coating, but in recent years generally do not paint, so naked. Since the tank is built to fill the oil there is an interval, some intervals of more than 1 year, the site will naturally seize the time to corrosion. In the ocean atmosphere, how much thickness can bare steel corrode and lose in a year? The low carbon steel data given by ISO 12944-2 are 80-200um/year 1 (C5-M).
    the reason for not painting is that thick oils such as crude oil can hang on the wall to prevent rust. I have not seen the state of this part of the oil tank, nearly a year without oil I have seen, rust is quite brilliant.
    how to paint here, should be applied oil-resistant electrostectrulated coating bar, can be thinner.
    oil can be dissolved in crude oil resin varnish, play the rust protection before loading oil, should also be suitable.
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