the quality guide

Visual assessment of surface cleanliness
ISO Standards 8501-1; 2007

  • For Rust Grades: record the assessment as the worst grade that is evident. For preparation grades record the assessment as that grade nearest in appearance to that of the steel surface.
  • Either in good diffuse daylight or in equivalent artificial illumination examines the steel surface and compare it with each of the photographs, using normal vision, place the appropriate photograph close to and in the plane of the steel surface to be assessed.
Rust Grade “A”
Rust Grade “A”Steel surface largely covered with adhering mill scale but little if any rust
Rust Grade “B”
Rust Grade “B”Steel surface which has begun to rust and from which the mill scale has begun to flake.
Rust Grade “C”
Rust Grade “C”Steel surface on which the mill scale has rusted away or from which it can be scraped, but with slight pitting visible under normal vision
Rust Grade “D”
Rust Grade “D”Steel surface on which the mill scale has rusted away and on which general pitting is visible under normal vision


  • In addition to the type of cleaning method used for example dry blast cleaning using a particular types of abrasive the following factors can influence the result of the visual assessment:
  1. Initial state of the steel surface other than any of the standard rust grades A,B,C and D
  2. Colour of the steel itself
  3. Regions of differing roughness, resulting from differential corrosion attack or uneven removal of materials.
  4. Surface irregularities such as dents
  5. Marks for tools
  6. Uneven lighting
  7. Shadowing of the surface profile caused by angled projection of abrasive.
  8. Embedded abrasive.
  9. For previously painted surfaces that have been prepared for renewed painting only photographs with rust grade designations D or C used for the visual assessment. The choice depends on the degree of pitting.
  10. The term “foreign matter” may include water soluble salts and welding residues. These contaminates cannot be completely removed from the surface by dry blast cleaning, hand and power tool cleaning or flame cleaning wet blast cleaning should be used.

Cleaning –Sa, St, FI

  1. Surface preparation by blast cleaning is designated the letters “Sa”
  2. Surface preparation by hand or power tool cleaning is designated the letters “St”
  3. Surface preparation by flame cleaning is designated the letters “FI”