Thickener Equipment is widely used in pulp and paper industry for washing and thickening of slurry. Apply for concentrating wood pulp, cotton pulp, reed pulp, rice and wheat straw, and also used for filtering other types of fiber suspension in other industry.
Features
1.This series of products have the advantages of Cylinder Mould rotated speed can be stepless changed according to the concentration of slurry and types of slurry.
2.Compact whole steel structure slurry tank, high capacity per unit area, good thickening effect,
3.Cylinder mould surface adopts plastic filter plate combined type, easy to replace and maintain, portable spray cleaning, filter can clean pulp thoroughly, low power consumption.
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Key words: underwater valve; anti-corrosion; paint; process CLC number: TQ320.6 Document code: A Article ID: 2095-2945(2019)01-0101-02
Under the strong corrosion environment of seawater, the paint on the outer surface of the valve needs to have a strong corrosion resistance to ensure that the valve is not corroded by seawater in The period of validity. This paper introduces the selection of anticorrosive paint for underwater valve and the spraying technology of paint to solve the corrosion resistance problem of the outer surface of underwater valve.
Keywords: underwater valve; anticorrosion; paint; process
1 The underwater environment analysis is classified according to the corrosion environment of ISO 12944: Corrosion protection of steel structure by protective paint system. The underwater (marine) environment belongs to C5-M (marine) heavy corrosion environment. Because there are more inorganic salts in seawater, seawater itself is a strong corrosive medium, coupled with the microbial and water mobility of water, which causes the paint on the surface of the valve to corrode severely, which will cause strong corrosion to the metal of the valve product itself. .
2 Anti-corrosion paint matching Due to the strong corrosiveness of the underwater environment, we must use paint with excellent anti-corrosion properties, and the paint must adapt to the underwater impregnation environment. According to "SH/T 3022-2011: Corrosion Design Specification for Petrochemical Equipment and Pipeline Coatings", select the inorganic silicate zinc-rich primer suitable for "the surface of steel with high corrosion resistance requirements", and use the thick film epoxy cloud for the intermediate paint. Iron paint, in the anti-corrosion coating system to enhance the shielding protection; the choice of topcoat, in addition to the need for strong anti-corrosion performance, also needs a good impregnation environment applicability, here we use low surface treatment epoxy resin paint The paint has better characteristics; according to the product recommended film thickness (dry film), the final choice is: inorganic silicate zinc-rich primer (75um) + epoxy cloud iron paint (125) + surface treatment ring Oxygen resin paint (100um).
3 Spray surface preparation roughness has a great influence on the base coating. The specific performance is three aspects. First, the greater the surface roughness, the unevenness of the surface of the substrate and the adhesion of the attached primer to each other, the adhesion is naturally greater; The greater the roughness, the larger the true surface area of ​​the substrate, the stronger the adsorption performance; the third is the greater the roughness, the corrosion products of the substrate are not easily diffused, and the influence of corrosion products on the adhesion is reduced. The outer surface of the valve is mostly machined surface, and the surface roughness is small, which is not conducive to the spraying of inorganic silicate zinc-rich primer. Therefore, sandblasting is usually used to increase the surface roughness and surface rust removal level of the substrate. The roughness can be recommended according to the paint instructions.
Prior to sand blasting, all welds, sharp edges, flanging and chamfering are sanded for smooth transition and all weld spatters are removed.
All surfaces (100%) before blasting should be free from any foreign matter such as flux, residue, lobes, oil, grease and salt.
Oil, grease or other surface contamination should be removed according to the specification SSPC-SP1.
All surfaces to be coated should be clean, dry and free of contaminants. All surfaces shall be evaluated and treated in accordance with ISO 8504:2000 prior to spraying.
4 Spraying process After the surface of the metal surface is sprayed, it is in a more active state, and it is very easy to chemically react with water in the air to cause rust. Therefore, the primer should be carried out within four hours after sandblasting.
Primers, intermediate paints and topcoats should not be used in any of the following situations:
(1) The surface of the pre-paint is moist or wet;
(2) Does the metal temperature exceed the dew point temperature by more than 5?埘 (3 ° C);
(3) When the relative humidity exceeds 85%;
(4) Is the temperature of steel or ambient air below 45? When 埘 (7 ° C).
The distance of the spray gun is controlled at about 30cm. The distance between the spray gun is too close, the spray is not well atomized, and it is easy to sag. If the spray gun is too far away, a considerable part of the paint will not spray on the surface of the workpiece, and the painting efficiency is low and a lot of waste is caused. As shown in Figure 1.
Painting sequence: If there are more irregular surfaces on the painted parts, you can spray/brush the hidden surface first, and then spray it as a whole to avoid local sag caused by repeated spraying of the enamel of metal powder (metal powder paint is more than ordinary paint) Easy to hang), affecting the appearance quality.
Spray gun adjustment: adjust the spray gun to the appropriate air pressure, flow rate and spray angle as much as possible to ensure the thickness of the paint film without sagging. The atomized paint should be sprayed to the largest possible fan surface. Workpiece surface to improve spray efficiency and spray quality.
5 Inspection methods and standards The inspection methods and standards involved in this process are as follows:
ISO 8504:2000: Preparation of Steel Substrates Prior to Use of Coatings and Related Products;
ISO 2409-2007: "Color paints and varnishes - cross-cut test", acceptance level: 0 to 2;
ISO 8501-1-2007: "Pre-treatment of steel before painting and related products, visual assessment of surface cleanliness", acceptance level: Sa 3;
ISO 8502-3: "Dust cleanliness standard for steel surface after blasting", acceptance level: 0 to 2;
In addition to the above tests, the appearance of the paint, the surface roughness after blasting, and the dry and wet film thickness were respectively detected by the corresponding testing instruments.
6 Possible problems and repairs If the inorganic zinc-rich primer film is too thick or over-coated, cracks will occur. In the event of cracking, the affected part must be completely removed by spraying.
For the repair of inorganic zinc primer, epoxy zinc-rich paint should be used. Inorganic zinc paint should not be used on the dried and solidified inorganic zinc primer. Otherwise, the adhesion will be poor and fall off.
7 Conclusion In the increasingly popular underwater oil production, underwater valve paint will play a very effective anti-corrosion function, the choice of anti-corrosion paint and spraying process is an important part of the whole project can not be ignored. The paint matching and spraying process recommended in this paper has been practiced for many years and the anti-corrosion performance is very good.
references:
[1] ISO 12944. Corrosion protection of steel structure by protective paint system [S].
[2] SH/T 3022-2011. Corrosion protection design specification for petrochemical equipment and pipeline coatings [S].
[3] ISO 8504: 2000. Paints and varnishes - cross-cut test [S].
[4] ISO 8501-1-2007. Pretreatment of steel before painting and related products, visual assessment of surface cleanliness [S].
[5]ISO 8502-3. Cleanliness standard of steel surface after sand blasting [S].
Abstract: Ocean underwater oil and gas exploitation is becoming more and more popular. Under the strong corrosive environment of seawater, the paint on the outer surface of the valve needs to have strong corrosion resistance, so as to ensure that the valve is not corroded by seawater during the effective period. The article introduces the selection of anti-corrosion paint for underwater valves and the spraying process of paint to solve the corrosion problem of the outer surface of underwater valves.