Main factors of anti-corrosion quality of anti-corrosion coatings and purchase items

The anti-corrosion construction of coatings is guided by engineering design documents.

In fact, the factors that affect the service life of coatings also include maintenance and repair of coatings

For example, if the surface treatment is lower than St3 level, rust surface coating or rust surface treatment agent is used.

1.

Influence of the original state of the steel on the service life of the coating

The pretreatment of steel before painting is affected by the original state of the steel, that is, the rust grade of the material

In the experiment, the Hongdan linseed oil paint was tested, and the difference in the service life of the coating was 50%

The influence of surface treatment factors

The surface treatment factor refers to the effect on the use of the coating when the design is basically correct, and cannot be understood as poor surface treatment

In the Code for Anti-corrosion Design of Industrial Buildings (GB50046-95), "Steel structure must be derusted before painting", and the minimum derusting level corresponding to the paint variety is listed in the table.

Although the specification does not discuss the durability relationship between surface treatment and coating varieties, it can be shown that the national specification has specific guidelines for the construction process of construction engineering coatings
.

The difference between the text description and the photo of "rust grade and rust removal grade of steel surface before painting" rust removal grade BSt3

Comparison of China's steel surface treatment standards with similar foreign standards Instructions "Very thorough hand and power tool rust removal: The steel surface should be free of visible grease and dirt, and free of loose scale, rust and paint coatings
.
Rust removal should be more thorough than St2, bottom The surface of the exposed part of the material should have a metallic luster
.
" The CSt3 photos in Part 5 of this standard have obvious traces of hand tools cleaning, showing a slight metallic luster, while the rust spots revealed in the BSt3 photos are still obvious, obviously untouched.
The rusted surface has been treated and is only suitable as a photo of a grade B or C rust
.

The national standard requires the corresponding surface treatment and rust removal grade for the selection of paint varieties.
The new project manager can prevent errors from several links such as design documents, construction tenders, and project supervision on-site management to ensure the quality of the painting project
.

2.
The influence of coating thickness on protection life

General rules for coating protection

The thickness of the coating film affects the anti-corrosion effect of the coating.
The oil-based anti-rust coating and the alkyd resin surface coating are matched with the exposure test.
The time required for the rust rate to reach % is proportional to the coating thickness, but the shrinkage caused by the increase of the coating thickness , cracks, spalling; the formation of temperature changes and the shrinkage rate of the coating surface are inconsistent, resulting in delamination and cracking of the coating film
.
Bridge steel structures are generally designed with a coating thickness of 200~250um.
When the coating thickness reaches 400um, the durability can be greatly increased
.
In fact, the designer will take an optimal point that comprehensively considers the coating cost, protective performance and maintenance cycle
.
The transmitting antenna tower of Shanghai TV station, bridges such as Nanpu and Yangpu, as well as the Oriental Pearl Steel Structure, etc.
, have followed this rule and have achieved good results
.

Design of coating thickness

Design and positioning of "Code for Design of Anti-corrosion of Industrial Buildings" (GB50046-95) Design and Positioning of "Code for Design of Anti-corrosion of Industrial Buildings" (GB50046-95), the rust removal level of important components that are not easy to maintain is increased from Sa2 to Sa2.
The thickness of the installation is increased by 20~60um, which ensures the protection requirements of important components and special parts of steel components
.

Precautions for the purchase of anti-corrosion coatings

1.
The environment

When purchasing anti-corrosion coatings, we must first consider the environment, and choose the appropriate anti-corrosion coatings according to the environmental location, temperature and humidity
.
For acidic media, phenolic resin paint with excellent acid resistance can be used, and for alkaline media, epoxy resin paint with excellent alkali resistance should be used
.

The feasibility of construction

When purchasing anti-corrosion coatings, it is also necessary to pay attention to the feasibility of construction conditions, and it is necessary to adopt suitable construction methods, such as: brushing, spraying, natural drying to form a film,
etc.
For the general case, we can choose a dry, easy-to-spray cold-set paint
.

3.
Consider supporting performance

How to choose a suitable anti-corrosion material, in addition to considering the environment and construction, should also pay attention to the matching system, matching the primer, intermediate paint and top coat, in order to maximize the performance and advantages of anti-corrosion coatings
.