Surface treatment standards

The surface treatment of steel should comply with the relevant regulations of the Steel Structures Painting Council (USA) or BS, GB and other specifications: SSPC-SP1 Solvent Treatment, SSPC-SP2 Hand Tool Treatment, SSPC-SP3 Power Tool Treatment, SSPC-SP10 Near White Sandblasting Treatment, SSPC-PA1 Factory, Site and Maintenance Paint, SSPC-PA2 Dry Film Thickness Measurement with Magnetic Gauge, BS 4232 Steel Sandblasting Rust Removal Surface Treatment Specification

Rust removal method

The rust removal of steel surfaces can be classified according to different methods. According to the order of rust removal, it can be divided into primary rust removal and secondary rust removal; According to the process stage, it can be divided into workshop raw material pretreatment, segmented rust removal, and overall rust removal; According to the rust removal methods, it can be divided into spray rust removal, power tool rust removal, manual shovel rust removal, and acid washing methods.

Preprocessing

The pre-treatment of steel surface refers to the removal of oxide scale, rust, and dirt and dust caused by external factors on the surface of steel through shot blasting or other methods on the steel pre-treatment assembly line before the primer is applied in the painting workshop. Secondly, surface pretreatment also includes removing floating rust, welding slag, dirt, and dust from steel surfaces that have already been coated with primer or workshop primer before applying anti-corrosion or decorative coatings.

Solvent cleaning

When performing solvent cleaning, specialized solvents should be used.

Wire brush cleaning

When using a wire brush for rust removal and cleaning, pneumatic or electric rotating wire brushes are generally used. This method is not suitable for removing oxide scales, but is suitable for pre-treatment of floating rust. If the surface after treatment has the following conditions: the rust on the surface has not been completely removed; The treated surface is too smooth, and the residual rust in the weld seam, as well as the presence of grease, dirt, etc. on the surface, are not conducive to painting. If painting is carried out in this situation, it will reduce the adhesion of the paint film and affect the effectiveness of the entire paint coating system. It is necessary to use a wire brush to clean and remove rust.

Knock shovel processing

The rust removal method of manual tapping or power tool tapping is usually used in conjunction with the wire brush rust removal method. This method is sometimes also applicable to surface treatment of steel with existing paint film and local repair coating of other paint systems. But this method is not suitable for surface pretreatment before coating epoxy or chlorinated rubber paints. This method can also be used to remove thicker rust layers, so that it can be more economical for future spray rust removal.

Grinding wheel rust removal

Grinding wheel rust removal is a method of using an elastic grinding wheel that rotates by wind or electric force to polish the surface of steel for rust removal. It is suitable for local rust removal and welding seam treatment. This is a more effective method of rust removal, which can achieve more satisfactory results than wire brush rust removal or shovel rust removal.

Pre treatment --->Solvent cleaning --->Wire brush cleaning --->Grinding wheel rust removal

Rust and rust removal standards

The corrosion and rust removal grade of steel surfaces before painting shall refer to the national standard GB8923-88 "Corrosion and rust removal grade of steel surfaces", which is equivalent to the Swedish standard SIS 055900-1967 "Rust removal standard of steel surfaces before painting" and the international rust removal standard ISO8501-1:1988. To distinguish the degree of corrosion and quality grade, China's GB8923-88 clearly compares and explains the various surface states and rust removal quality grades of steel with photos. The inspected surface is observed vertically, but cannot be compared with a magnifying glass.

Corrosion grade

The four levels of corrosion on the surface of steel are represented by A, B, C, and D, respectively, and their wording is as follows:

A. The steel surface is covered with metal oxide scale and has almost no rust. B. The steel surface has rusted and some oxide scales have peeled off. C. The oxide scale has peeled off due to corrosion or can be scraped off, and there is a small amount of pitting corrosion on the steel. D. The oxide scale has been completely peeled off due to corrosion, and pitting corrosion has occurred on the surface of the steel.

Rust removal grade

The rust removal grade on the surface of steel is represented by English letters plus Arabic numerals, such as Sa2.5. The preceding English letters indicate rust removal methods, St and Sa respectively represent manual rust removal and spray rust removal methods. The Arabic numerals at the end indicate the rust removal level, which refers to the degree of adhesion of oxide scale, rust, and old paint (adhesion refers to welding slag, welding spatter, soluble salts, dirt, grease, etc.).

The letter representation of rust removal method is as follows:

Sa - Spray or shot blasting rust removal method. St - Rust removal method for manual and power tools, such as shovels, manual or power elastic grinding wheels or grinding wheels.

Spray rust removal grade

There are four rust removal levels for steel surfaces that have been treated with spray or shot blasting, and their wording is as follows:

Sa1- indicates mild spray or shot blasting rust removal. The surface of the steel should be free of visible oil stains and dirt, and there should be no loosely attached oxide scales, rust, or old paint coatings. Sa2- indicates thorough spraying or shot blasting for rust removal. The surface of the steel should be free of visible grease and dirt, and the attachments such as oxide scale, rust, and old paint coatings have been basically removed. The residue should be firmly attached. Sa2.5- indicates thorough spraying or shot blasting for rust removal. The surface of the steel should be free of visible attachments such as grease, dirt, oxide scale, rust, and paint coatings. Any residual traces should only be slight color spots in the form of dots and stripes. Sa3- Refers to spraying or shot blasting to clean the surface of steel for rust removal. The surface of the steel should be free of visible attachments such as grease, dirt, oxide scale, rust, and paint coatings, and the surface should display a uniform metallic luster.

Manual rust removal grade

When manual tool cleaning is specified, the contractor must ensure that the manual tool cleaning complies with SSPC SP2 63 or equivalent. Manual and power tools, such as shovels, manual or power wire brushes, power elastic grinding wheels or grinding wheels, etc., should first remove the thick rust layer and remove grease and dirt for rust removal. After manual rust removal, the surface of the steel should be cleaned of floating dust and debris. There are two rust removal levels, St2 and St3. Generally used on steel surfaces without oxide scale. The wording is as follows:

St2- indicates thorough manual and power rust removal, with no visible grease or dirt on the steel surface, and no loosely attached oxide scales, rust, or old paint coatings. St3- indicates very thorough manual and power tool rust removal. The surface of steel should be free of visible grease and dirt, and there should be no loosely attached oxide scale, rust, paint coatings, or other attachments. Rust removal should be more thorough than St2, and the surface of the exposed part of the substrate should show a metallic luster.

Rust removal grade of electric tools

When specifying the cleaning of power tools, the contractor must ensure that the cleaning of power tools complies with SSPC SP3 63 or Swedish standard ST3 or equivalent.