Degree of purity (steel)

Formerly "standard purity", standard term (ISO 12944) today "surface preparation level". Various institutions have defined standards for the surface preparation of steel , so-called degrees of cleanliness . They assess the purity of the surface of a component with regard to adhering particles or the existing wetting with fluids. The surface preparation is used for a subsequent coating ( anti-corrosion coating ). A certain degree of purity is usually required by the manufacturer of a coating or the owner of a project and is defined in the tender documents.

The specification of the content of non-metallic inclusions in the material, which influence its performance properties, is dealt with in the article Purity grade (material) .

Common standards

The most frequently used and internationally widely recognized standards for surface preparation are: NACE (National Association of Corrosion Engineers), SSPC (Steel Structures and Paint Council), the Swedish Standard (according to SIS 05 5900) and the English Standard (according to BS 4232, United Kingdom Standards). In Europe , the classification according to the Swedish standard has prevailed.

The ISO standard (DIN EN) ISO 12 944 as well as the now withdrawn German standard DIN 55 928 and DIN EN ISO 8501-1 (basis for DIN EN ISO 12 944) correspond to the classification according to the Swedish standard.

Classification according to the Swedish standard SIS 05 5900

In combination with the rust grades A, B, C and D (non-corroded mill skin, partially rusted mill skin, completely rusted mill skin / full-surface rust with at most small pits, rust with strong pitting), different optical appearances result for the surface preparation grades apart from Sa 3. The type of blasting agent (e.g. melting chamber slag (dark) / chrome ore slag, garnet sand (light)) leads to surfaces of different lightness (especially SA 2 ½ and Sa 3), so that the photos shown in the standard are only an approximate approximation which may differ in individual cases.

SA 1 - "Brush-off Blast Cleaning"

The surface is defined as free of oil , grease , dirt, loose scale (burn-off) , loose rust and loose paint or coating. Remaining scale, rust and paint should be firmly adhering and the surface should be sufficiently roughened in order to achieve good adhesion of the coating to be applied.

A surface according to standard SA 1 is comparable to SP-7 (SSPC) and NACE 4

SA 2 - "Commercial Blast Cleaning"

The surface is defined as free of any oil, grease, dirt, scale, rust, paint and other foreign bodies. Only slight traces or discoloration due to rust or scale or slight, adherent residues of paint or coating may remain. Slight residues of rust or paint may remain in the depressions on a roughened surface. At least 2/3 of every square inch should be free of visible residues and these should be limited to only slight discoloration, stains or small residues of the substances mentioned.

A surface according to standard SA 2 is comparable to SP-6 (SSPC), NACE 3 and Third Quality (British standard)

SA 2 ½ - "Near White Blast Cleaning"

The surface is defined as free of any oil, grease, dirt, scale, rust, corrosion , oxides , paint and other foreign bodies. Only slight traces or discoloration due to rust or scale and slight, adherent residues of paint or coating may remain. At least 95% of every square inch should be free of visible residues and these should be limited to only slight discoloration, stains or small residues of the substances mentioned.

A surface according to the SA 2 ½ standard is comparable to SP-10 (SSPC), NACE 2, Second Quality (British standard)

SA 3 - “White Metal Blast Cleaning”

The surface is defined as having a uniform gray-white metallic appearance, slightly roughened in order to enable good adhesion of the coating to be applied. When viewed without magnification, the surface should be free of any oil, grease, dirt, visible scale, rust, corrosion products, oxides, paint or other foreign bodies.

A surface according to standard SA 3 is comparable to SP-5 (SSPC), NACE 1, First Quality (British standard)

ST 3 - "Power Tool Cleaning"

Removal of all rust, scale, loose rust, and paint using machine-operated wire brushes , scraping or sanding tools, or a combination of these methods. The surface should be shiny metal and free from oil, grease, dirt, earth , salt or other impurities. The surface should not be polished or smoothed.

ST 2 - "Hand Tool Cleaning"

Removal of all rust, scale, loose rust and loose paint by hand working with a wire brush, sandpaper , grinding tools, by hand tapping or scraping off or a combination of these methods.

Comparability of the standards

While each institution uses a different terminology and the defined requirements differ slightly from one another, the standards can still be compared.

Swedish SIS 05 5900	German DIN 55 928	International ISO standard 8501-1	American SSPC-SP	NACE	English BS 4232
SAT 3	SAT 3	SAT 3	SSPC-SP5 White Metal Blast Cleaning	NACE 1	First quality
SA 2 ½	SA 2 ½	SA 2 ½	SSPC-SP10 Near White Metal Blast Cleaning	NACE 2	Second quality
SAT 2	SAT 2	SAT 2	SSPC-SP6 Commercial Blast Cleaning	NACE 3	Third quality
Sat 1	Sat 1	Sat 1	SSPC-SP7 Brush-Off Blast Cleaning	NACE 4	-
ST 3	ST 3	ST 3	SSPC-SP3 Powertool Cleaning	-	-
ST 2	ST 2	ST 2	SSPC-SP2 Hand Tool Cleaning	-	-

Web links

• "Surface Preparation Standards" including a description of the SSPC standards

Individual evidence

1. ↑ The steel cleaning by means of blasting - sandblasting
2. ↑ Surface Preparation Standards  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF file, English; 66 kB)  
3. ↑ Surface Preparation Standards (English)