Rust and Derusting Grade of Steel Surface (Before Painting)

This standard specifies the visual evaluation grade of rust degree and rust removal quality of steel surface before painting.

It is applicable to hot rolled steel surfaces treated by spraying or jetting, manual and power tool rust removal and flame rust removal.

The evaluation of rust removal grade on the surface of cold rolled steel can also be referred to.

This standard is equivalent to the international standard ISO8501-1:1988 Preparation of Steel before Application of Paints and Related Products – Visual Assessment of Surface Cleanliness – Part 1: Rust Grades and Derusting Grades of Uncoated Steel and Steel after Overall Removal of the Original Coating

Rust and Derusting Grade of Steel Surface (Before Painting) 1

1. General

1.1 This standard divides the original rust degree of uncoated steel surface into four “rust grades”, and divides the quality of uncoated steel surface and steel surface completely cleaned of the original coating into several “rust removal grades”.

The rust grade and derusting grade of the steel surface shall be determined jointly by written descriptions and photos of typical samples.

1.2 This standard expresses the rust grade and derusting grade based on the visual appearance of steel surface.

When evaluating these grades, observe directly with normal vision under moderate lighting conditions without the aid of magnifying glass and other instruments.

2. Rust grade of steel

The four rust grades of steel surface are indicated by A, B, C and D.

These corrosion grades are described as follows:

A. The steel surface is completely covered with oxide skin and almost free of rust;

B. Steel surfaces that have been rusted and some oxide scales have been peeled off;

C. Steel surface whose oxide skin has been peeled off due to corrosion, or can be scraped off, and has a small amount of pitting corrosion;

D. Steel surface where the oxide skin has been completely peeled off due to corrosion and pitting corrosion has occurred generally.

Rust and Derusting Grade of Steel Surface (Before Painting) 2
Rust Grades

3. Derusting grade

3.1 General

3.1.1 The derusting grade of steel surface is indicated by the letters “Sa”, “St” or “FI” representing the derusting method used.

If the letter is followed by an Arabic numeral, it indicates the degree of removal of scale, rust, paint coating and other attachments.

3.1.2 For the text description of the derusting grade of steel surface, see 3.2, 3.3 and 3.4.

Note:

(1) In the definitions of rust removal grades in this chapter, the term “attachment” can include welding slag, welding spatter, soluble salts, etc.

(2) When “oxide skin, rust or paint coating” in this chapter can be peeled off from the steel surface with a metal putty scraper, it shall be considered as not firmly attached.

3.2 Rust removal by spraying or jetting

3.2.1 The letter “Sa” is used for spray or shot derusting.

3.2.2 Thick rust layer shall be removed before spraying or jetting.

Visible grease and dirt should also be removed. After rust removal by spraying or jetting, the steel surface shall be cleaned of floating ash and debris.

3.2.3 There are four rust removal grades in this standard for steel surfaces that have been sprayed or shot for rust removal.

The text is as follows:

Sa1 Mild spray or shot derusting;

The steel surface shall be free of visible grease and dirt, and free of loose oxide skin, rust, paint coating and other attachments.

See photos BSa1.CSal and DSa1

Rust and Derusting Grade of Steel Surface (Before Painting) 3
Sa1 mild spray or shot derusting

Sa2 Thoroughly spray or blast rust removal

The steel surface shall be free of visible grease and dirt, and the attachments such as scale, rust and paint coating have been basically removed, and the residues shall be firmly attached.

See photos BSa2, CSa2 and DS2.

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Sa2 Thorough spray or projection deburring

Sa21/2 Very thorough spray or shot rust removal

The steel surface shall be free of visible attachments such as grease, dirt, oxide skin, rust and paint coating, and any residual trace shall be only a slight spot or stripe.

See photos ASa21/2, BSa1/2, CSa1/2, and DSa21/2

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Sa21/2 Very thorough derusting by shooting or throwing

Sa3 Spraying or jetting to make the steel surface clean

The steel surface shall be free of visible attachments such as grease, dirt, oxide skin, rust and paint coating, and the surface shall show uniform metal color.

See photos ASa3, BSa3, CSa3 and DSa3

Rust and Derusting Grade of Steel Surface (Before Painting) 6
Sa3 Spraying or jetting to make the steel surface clean

3.3 Derusting of manual and power tools

3.3.1 Use manual and power tools, such as blade, manual or power wire brush, power sandpaper tray or grinding wheel, to remove rust, which is indicated by the letter “St”.

3.3.2 Before derusting with manual and power tools, the thick rust layer shall be removed, and visible grease and dirt shall also be removed.

After rust removal with manual and power tools, the steel surface shall be cleaned of floating dust and debris.

3.3.3 For the steel surface that has been derusted by hand and power tools, this standard has two derusting grades, and the text description is as follows:

St2 Thorough manual and power tool derusting

The steel surface shall be free of visible grease and dirt, and free of loose oxide skin, rust, paint coating and other attachments.

See photos BSt2, CSt2 and DSt2.

Rust and Derusting Grade of Steel Surface (Before Painting) 7
St2 Thorough manual and power tool derusting

St3 very thorough manual and power tool derusting

The steel surface shall be free of visible grease and dirt, and free of loose oxide skin, rust, paint coating and other attachments.

Rust removal shall be more thorough than St2, and the surface of exposed parts of the substrate shall have metallic luster.

See photos BSt3, CSt3 and DSt3.

Rust and Derusting Grade of Steel Surface (Before Painting) 8
St3 very thorough manual and power tool derusting

3.4 Flame derusting

3.4.1 Flame derusting is indicated by the letter “FI”.

3.4.2 Before flame derusting, the thick rust layer shall be removed.

Flame derusting shall include the products attached to the steel surface after the flame heating operation and heated by power wire brush.

3.4.3 The derusting grade after flame derusting is described as follows:

The steel surface shall be free of oxide scale, rust, paint coating and other attachments, and any residual traces shall only be surface discoloration (shadows of different colors).

See photos AFI, BFI, CFI and DFI

Rust and Derusting Grade of Steel Surface (Before Painting) 9
FI flame derusting

4. Visual evaluation of rust grade and rust removal grade of steel surface

4.1 The rust grade and rust removal grade of steel surface shall be evaluated under good scattered sunlight or artificial lighting conditions with equivalent illuminance.

The inspector shall have normal vision.

4.2 The steel surface to be inspected shall be visually compared with the corresponding photos (see Chapter 5).

Photographs should be close to the steel surface.

4.3 When evaluating the corrosion grade, the corrosion grade indicated in the photo of the corresponding severely rusted grade shall be taken as the evaluation result;

When evaluating the derusting grade, the derusting grade indicated in the photo closest to the appearance of the steel surface shall be taken as the evaluation result.

Note:

(1) There are many factors affecting the visual evaluation results of the derusting grade of steel surface, mainly including:

  • a. Abrasives used for spraying or jetting rust removal, and tools used for manual and power tool rust removal;
  • b. Rust status of steel surface that does not belong to standard corrosion grade;
  • c. The color of the steel itself;
  • d. The roughness of each part is different due to different corrosion degree;
  • e. The surface is uneven, such as dents;
  • f. Tool scratches;
  • g. Uneven lighting;
  • h. Shadows caused by different angles of abrasive impact on the surface during rust removal by spraying or projection;

(2) Visually assess the rust grade of the originally coated steel surface.

Only photos with rust grade symbols C and D (such as DSt21/2 and CSt21/2) can be used.

The choice of which one (such as DSt21/2 or CSt21/2) depends on the degree of pitting on the steel surface.

5. Photos

5.1 This standard includes 28 photos of typical sample plate of steel surface rust grade, which are the same as those in the international standard ISO 8501 – 1:1988.

In case of any objection, the photos in ISO 8501 – 1 shall be used as the basis for arbitration.

5.1.1 There are 4 photos showing the corrosion grade, marked with A, B, C and D.

5.1.2 There are 24 photos showing the derusting grade achieved by spray or projection derusting, manual and power tool derusting and flame derusting.

These photos are marked with the symbols of the original rust grade before and after rust removal, such as BSa21/2

5.2 Fourteen photos of spray or shot derusting show the surface condition of steel after dry spray derusting with quartz sand abrasive.

When other kinds of abrasive are used for spray or shot derusting, the surface of steel after derusting may have different colors.

5.3 This standard does not contain photos of ASa1, ASa2, ASt2 and Ast3.

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