ISO/TR 22770:2019 PDF

Overview

ISO/TR 22770:2019 provides guidance on using analytical colorimetry (portable colorimeters and spectrophotometers) to support the visual assessment of surface preparation grades for steel substrates as described in ISO 8501-1:2007, Clause 4. The technical report shows how objective colour measurements in the CIELAB (Lab)* space and calculated colour differences (ΔE*) can be used as a rapid, reproducible complement to traditional visual inspection. Data examples follow the methodology in Annex A of the report.

Key topics and technical requirements

• Principle: Assess preparation grade by computing colour component differences relative to a reference substrate with the targeted preparation grade; acceptability is based on agreed ΔE* limits between parties.
• Colour space and metrics: Uses CIE 1976 L a b*** coordinates and ΔE* (Euclidean colour difference). Related components (ΔL*, Δa*, Δb*, ΔC*, ΔH*) are defined.
• Instruments: Both spectrophotometers and tristimulus colorimeters (portable types) are suitable. Manufacturers’ specifications should be followed.
• Instrument handling: Ensure close contact with the surface, avoid stray light, maintain constant instrument-to-surface distance, and avoid measurements in very dusty environments.
• Measurement conditions: Fix illuminant, observer (CIE 1931 or CIE 1964 supplemental), and geometric conditions (e.g., 45/0° geometry is commonly used). See CIE 15 for geometric terminology.
• Supporting data & methodology: The report outlines sample preparation, data collection, and presentation of results. Annex A describes the specific methodology used for the example data.

Practical applications

ISO/TR 22770:2019 is intended to make surface cleanliness assessment:

• More objective and reproducible than visual-only methods
• Faster for routine quality control and acceptance decisions

Typical use cases include:

• Quality control of blast-cleaning prior to anticorrosion coatings (steel pipes, freight wagons, trailers)
• Inspection of desanding/descaling operations in foundries and cold-drawn bar production
• On-site acceptance testing by coating specifiers, inspectors, and contractors

Benefits: supports contractual acceptance criteria, reduces subjectivity in visual grades, enables quick pass/fail checks when reference substrates and ΔE* tolerances are agreed.

Who should use this standard

• Coating specifiers and system designers
• QA/QC inspectors and coating contractors
• Steel producers, fabricators and manufacturers (pipes, wagons, automotive parts)
• Laboratory and field testing personnel using portable color measurement instruments

Related standards

• ISO 8501-1 (visual assessment of rust and preparation grades) - primary reference
• ISO 8502 series, ISO 8503 series, ISO 8504 series (related surface cleanliness and preparation guidance)
• CIE publications (CIE 15, CIE 1931/1964 observers) for measurement geometry and observers

Keywords: ISO TR 22770:2019, analytical colorimetry, colorimeter, spectrophotometer, surface preparation grades, ISO 8501-1, CIELAB, ΔE, steel substrates, visual assessment, surface cleanliness.