Commonly used paint selection for steel structure anti-corrosion-WANJINLONG

1. Selection for anti-corrosion paint

After the surface of the derusted steel is inspected, it shall be painted within the required time limit. The anti-rust coating should generally consist of a primer, an intermediate paint and a finishing coat. The choice of paint should be based on the matching of the paint and the derusting grade, and the matching combination of the primer and the finishing coat.

1.1 Commonly used paint

The performance, application, paint methods and accessory requirements of commonly used anti-rust primers, finishing coats and anti-corrosion paints are listed in the below table.

Commonly used anti-rust primers
Item	Performance	Application	Paint method	Accessory requirements
Epoxy zinc-rich primer	Excellent anti-corrosion performance, good mechanical properties, strong adhesion, high zinc powder content in the paint film, cathodic protection and excellent water resistance performance	Suitable for pre-coating primers in the workshop (used in steel structure workshops)	Brush or spray	Matching with fluorocarbon finishing coat
Iron red oilbaseanti rust paint	Good anti-rust performance, strong paint film, strong adhesion, but the drying is slow	Suitable to the anti-rust base of steel structure surface, but can not be used for aluminum and zinc because of electrochemical action	Brush	Matching with ester enamel enamel, phenolic enamel, alkyd enamel
Iron red oil antirust paint	strong adhesion, good anti-rust performance, but less than iron red oilbaseanti rust paint	Suitable for anti-rust base of steel structure surface with low anti-rust requirements	Brush	Matching with ester enamel enamel, phenolic enamel
Red phenolic antirust paint	good anti-rust performance, strong paint film, strong adhesion, the drying is fast	Same with Iron red oilbaseanti rust paint	Brush	Matching with ester enamel enamel, phenolic enamel
Iron red phenolic antirust paint	Strong adhesion, soft paint film, poor wear resistance, anti-rust performance is only inferior to red phenolic anti-rust paint	Suitable for anti-rust base of steel structure surface with less anti-rust requirements	Brush or spray	Matching with phenolic enamel
Iron red, gray phenolic primer	The paint film has good adhesion and certain anti-rust performance	Suitable for anti-rust base of steel structure surface with less anti-rust performance requirements	Brush or spray	Matching with alkyd enamel and pure phenolic enamel
Iron red pure phenolic primer	certain anti-rust performance and good water resistance performance	Suitable for anti-rust base of steel structure surface with less anti-rust performance requirements	Brush or spray	Matching with alkyd enamel and pure phenolic enamel
Various color barium borate phenolic antirust paint	It has good resistance to atmospheric rust, fast drying and convenient construction. Gradually replace part of red lead rust-proof paint, save lead, non-toxic	Suitable for anti-rust base of steel structure surface	Brush or spray	Matching with phenolic enamel, alkyd enamel
Iron red, gray ester rubber primer	The paint film is hard, easy to sand and has good adhesion	Suitable for anti-rust base of steel structure surface with less anti-rust requirements	Brush or spray	Matching with blending varnish and phenolic enamel
Red lead alkyd antirust paint	good anti-rust performance, strong paint film, strong adhesion, the drying is fast	Same with Iron red oilbaseanti rust paint	Brush or spray	Matching with alkyd enamel and ester enamel
red iron oxide alkyd primer	good adhesion and certain anti-rust performance, and has good durability under normal climatic conditions, but has poor durability in wet tropical climate and humid conditions.	Suitable for professional anti-rust base of general steel structure	Brush or spray	Matching with alkyd enamel, nitro enamel, asphalt lacquer, perchloroethylene lacquer, etc.
Vinyl phosphating primer	The adhesion to the steel surface is strong, and the phosphate in the paint can form a phosphate film on the surface of the steel to prolong the lifetime of the organic coating.	Suitable to the anti-rust base of steel structure surface, it can save the phosphating fire passivation treatment, but can not replace the general primer, not suitable for the environment with alkaline medium	Brush or spray	matching with other anti-rust paints, primers and finishing coat
Iron oxide red perchlorovinyl primer	has certain rust and chemical resistance, but its adhesion to steel is not very good. If it is used together with phosphating primer, it can withstand maritime and wet tropical climate.	Suitable for anti-rust base of steel structure surface in coastal areas and hot and humid conditions	Brush or spray	Matching with phosphating primer and perchloroethylene anti-rust paint
Iron red epoxy ester primer	The paint film is hard and durable, and has good adhesion. When used together with the phosphating primer, it can improve the moisture resistance, salt spray resistance and rust resistance of the paint film.	Suitable for anti-rust base of steel structure surface in coastal areas and hot and humid conditions	Brush or spray	Matching with phosphating primer and epoxy enamel, epoxy anti-rust paint
Micaceous iron oxide primer	Good thermal stability, alkali resistance, anti-rust performance is better than red lead and boron enamel anti-rust paint, non-toxic, low in price and abundant raw materials.	Suitable for anti-rust base of steel structure surface under tropical climate and hot and humid conditions	Brush or spray	Matching with all types of finishing coat
inorganic zinc-rich primer	It has good water resistance, oil resistance, solvent resistance, heat resistance and resistance to dry and wet salt spray. It has cathodic protection and long-term exposure but not aging.	Suitable for anti-rust base of steel structure building surface such as water towers, water tanks, oil tanks and marine steel structures	Brush or spray	It can be used as a finishing coat, the effect will be better if it is matching with epoxy enamel and vinyl enamel

Commonly used finishing paint
Item	Performance	Application	Paint method	Accessory requirements
Fluorocarbon coating	Excellent fading resistance, anti-blooming, anti-air pollution (acid rain, etc.), strong UV resistance, strong crack resistance and ability to withstand harsh weather conditions	Mainly used for high-performance finishing coats and durable finishing coat in anti-corrosion coating systems with high requirements	Airless spray	Matching with epoxy zinc-rich primer
Colored oil blending paint	Weather resistance is better than ester rubber blending paint, but drying time is longer, paint film is softer	Suitable for the finishing paint of indoor normal steel structure	Brush
Colored ester rubber blending paint	The drying performance is better than the oily blending paint, the paint film is hard and has certain water resistance.	Suitable for the finishing paint of normal steel structure	Brush or spray
Colored phenolic enamels	The paint film is hard, shiny and has good adhesion, but the weather resistance is poor.	Suitable for the finishing paint of indoor normal steel structure	Brush or spray	Matching with ester rubber primer, iron red lead antirust paint, gray antirust paint and iron red antirust paint
Various pure phenolic enamels	Hard film, good water resistance and weather resistance	Suitable for the finishing paint of damp-proof and alternating moisture and dryness steel structure	Brush or spray	Matching with various anti-rust paints and phenolic primers
Colored alkyd enamels	Good weather resistance and good adhesion, but slow drying	Suitable for the finishing paint of steel structure	Brush or spray	Firstly spray 1~2 times C06-1 iron red alkyd primer first, then spray 2 times C06-1 alkyd primer, and finally spray this paint.
Gray phenolic antirust paint	Good weather resistance, certain water resistance and rust resistance	Suitable for the finishing paint of steel structure	Brush or spray	Matching with Hongdan Fire Iron Red Antirust Paint
Colored vinyl chloride anticorrosive paint	Excellent corrosion resistance and moisture resistance. However, the adhesion is poor, but if there a good matching, this shortage can be made up. If baked at 60~65 °C for 1-3 hours, its various mechanical properties are superior to those of nitrocellulose lacquer.	suitable for the finishing paint of steel structure against the corrosion of acid mist	Brush or spray	Matching with X06-1 ethylene phosphating primer and C06-4 iron red perchloroethylene primer
Colored epoxy nitro enamel	Good weather resistance, high physical and mechanical strength, good oil resistance	suitable for finishing coat of steel structure against industrial atmospheric corrosion in hot and humid climates	Brush or spray	Matching with epoxy primer
Asphalt varnish	Good water resistance, moisture and corrosion resistance, but poor mechanical properties, poor weather resistance	Suitable for the primer and finishing coat of steel structure against acid air	Brush or spray	This primer is also used as finishing paint, normally spray for 2 times
Asphalt acid resistant paint	Good sulfuric acid corrosion resistance and good adhesion	Suitable for the primer and finishing paint of anti-rust indoor steel structure	Brush or spray	This primer is also used as finishing paint, normally spray for 2 times
Polyurethane finishing coat (acrylic acid)	The coating is tough, beautiful, excellent adhesion, outstanding wear resistance and corrosion resistance, water resistance, salt water resistance and solvent resistance are excellent, and the coating durability is good.	Mainly used for anti-corrosion decorative finishing coat for mechanical equipment, machine tools, indoor steel structures, light steel structures, etc.	Airless spray
Chlorinated rubber finishing coat	The film is tough and has excellent weather resistance and chemical resistance.	Used in ships, port facilities, chemical equipment and bridges.	Brush or spray

In heavy anti-rust systems, the primary role of the intermediate paint is to enhance the shielding role of the whole coating system by increasing the thickness of the coating. The most commonly used intermediate paint is an epoxy cloud iron intermediate paint.

Commonly used finishing paint
Item	Performance	Application	Accessory requirements
Epoxy cloud iron intermediate paint	Good adhesion, flexibility, wear resistance and sealing properties.	It can be used as an intermediate layer of high-performance anti-rust primer to protect the primer film and enhance the protection performance of the entire coating.	Matching with epoxy iron red primer, epoxy zinc-rich primer, inorganic zinc primer

1.2 Paint matching combination

The matching combination of anti-rust primer, intermediate paint and finishing coat used in steel structure project are as the following table:

The matching combination of primer, intermediate paint and finishing coat used in steel structure project

No.	Primer and intermediate paint	Finishing paint	Lowest anti-rust grade	Applicable environmental components
1	Red Lead series (oily antirust paint, alkyd or phenolic antirust paint) primer 2 times; Iron red series (oily antirust paint, alkyd primer, phenolic antirust paint) primer 2 times; Cloud iron alkyd antirust paint primer 2 times.	Various colors of alkyd enamel 2-3 times	St2	Non-erosion components
2	Chlorinated rubber primer 1 time	Chlorinated rubber finishing coat 2-4 times	Sa2	1. Important components of weak erosion in indoor and outdoor areas; 2. Various load-bearing structures in moderately erosive environments
3	Chlorosulfonated polyethylene primer 2 times; chlorosulfonated polyethylene intermediate paint 1-2 times;	Chlorosulfonated polyethylene finishing coat 2-3 times
4	Iron red epoxy ester primer 1 time; epoxy anti-corrosive paint 2-3 times;	Epoxy clear (color) paint 1-2 times
5	Iron red epoxy primer 1 time; Epoxy cloud iron intermediate paint 1-2 times	Chlorinated rubber paint 2 times
6	Polyurethane primer 1 time; Polyurethane enamel 2-3 times	Polyurethane varnish 1-3 times
7	Epoxy zinc-rich primer 1 time; Epoxy cloud iron intermediate paint 2 times	Chlorinated rubber finishing coat 2 times
8	Inorganic zinc-rich primer 1 time; Epoxy cloud iron intermediate paint 1 time	Chlorinated rubber finishing coat 2 times	Sa2*1/2	The important structure need to strengthen the anti-corrosion
9	Inorganic zinc-rich primer 2 times + epoxy intermediate paint 2-3 times(75~100μm)+(75~125μm)	Polyurethane finishing coat 2 times(50μm)	Sa2*1/2

2. Galvanized

2.1 Overview

Galvanized refers to a surface treatment technique that coats a layer of zinc on the surface of a metal, alloy or other material to achieve the effect of aesthetics, rust prevention, and etc. Can be divided into two types: hot galvanized and cold galvanized. The main method currently used is hot galvanized.

2.2 Classification

2.2.1 Hot galvanized

Hot galvanized, also known as hot-dip galvanized, is a method that the steel components present a non-staining and wetting surface after surface oil and rust removal and then immediately been immersed in a plating tank that has been previously melted by zinc to form a surface of galvanized . The hot-dip galvanized coating is thicker, generally 30-60 microns, and the coating has a higher corrosion resistance. It is suitable for the steel components outdoor, such as highway fences, power towers, large-size fasteners and other relatively "rough" workpieces for long-term rust prevention. The older iron pipes are also hot-dip galvanized.

2.2.2 Cold galvanized

Also known as electroplating zinc, is a method that the steel components present a non-staining and wetting surface after surface oil and rust removal and then hung on the cathode of a special plating tank, and the anode is made of zinc., and when the DC power is turned on, the zinc ions on the anode migrate to the cathode, and discharge on the cathode, so that it is plated with a zinc layer. The surface of the cold-galvanized workpiece is smooth and flat, but because the coating is relatively thin, generally within 5-30 microns, the corrosion prevention time will be shorter. They are used for rust prevention of indoor parts, such as chassis bottoms, panels, and small-sized fasteners.

2.3 Quality characteristics

Smooth appearance, no zinc, burr, silvery white; thickness is controllable, arbitrarily selected within 5-107μm; no hydrogen embrittlement, no temperature hazard, can ensure the mechanical properties of the material unchanged; can replace some parts need hot-dip galvanized process; good corrosion resistance, neutral salt spray test can last for 240 hours.

2.4 Application range

Mainly used in steel nails, nails, fasteners, water pipe joints, scaffolding fasteners, wire rope horse steel chucks. In recent years, with the development of galvanized technology and the use of high-performance galvanizing brighteners, galvanized has entered the protective-decorative application from the purely protective purpose.

3. Comparison with paint

Item	Process	Main application	Advantage	Disadvantage
Steel structure paint	3 times(primers, intermediate paint and finishing coat)	All types of steel structure	On-site materials, general workers can paint directly	Easy to fall off, often maintained, the paint quality may not be good
galvanized	1 time	Generally for the secondary steel structure such as purlin and brace	Smooth surface, not easy to age, good corrosion resistance	Need to go to another professional galvanized company for galvanized, increase transportation costs, etc.