ISO/TR 22770:2019

TECHNICAL ISO/TR
REPORT 22770
First edition
2019-07
Preparation of steel substrates before
application of paints and related
products — Analytical colorimetry
method to support visual assessment
of surface preparation grades
Reference number
ISO/TR 22770:2019(E)
©
ISO 2019

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ISO/TR 22770:2019(E)

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ISO/TR 22770:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Principle . 2
6 Recommendations for instruments . 3
6.1 Instrument handling . 3
6.2 Instrument specifications . 3
6.2.1 Illuminant and observer . 3
6.2.2 Illuminating and viewing conditions. 3
6.2.3 Tolerance of the instrument . 4
7 Supporting data . 4
7.1 General . 4
7.2 Sample preparation . 4
7.3 Results . 4
8 Examples of application . 5
8.1 General . 5
8.2 Steel pipes producer for oil and gas industry . 5
8.2.1 Application: control quality of blasting operation prior to anticorrosion coating . 5
8.2.2 Reference substrate . 6
8.2.3 Quality control . 6
8.3 Cast iron foundry . 6
8.3.1 Application: control quality of desanding operation of cast iron
automotive parts . 6
8.3.2 Reference substrate . 6
8.3.3 Quality control . 6
8.4 Trailers manufacturer . 6
8.4.1 Application: control quality of blasting operation prior to painting . 6
8.4.2 Reference substrate . 6
8.4.3 Quality control . 7
8.5 Production of freight wagons . 7
8.5.1 Application: control quality of blasting operation prior to anticorrosion coating . 7
8.5.2 Reference substrate . 7
8.5.3 Quality control . 7
8.6 Cold drawn bars producer . 7
8.6.1 Application: optimisation of descaling operation . 7
8.6.2 Reference substrate . 7
8.6.3 Quality control . 7
Annex A (informative) Methodology . 8
Bibliography .11
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ISO/TR 22770:2019(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee
SC 12, Preparation of steel substrates before application of paints and related products.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
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ISO/TR 22770:2019(E)

Introduction
The performance of protective coatings of paint and related products applied to steel is significantly
affected by the state of the steel surface immediately prior to painting. The principal factors that are
known to influence this performance are
a) the presence of rust and mill scale,
b) the presence of surface contaminants, including salts, dust, oils and greases, and
c) the surface profile.
The ISO 8501 series, the ISO 8502 series and the ISO 8503 series provide methods for assessing these
factors, while the ISO 8504 series provides guidance on the preparation methods that are available for
cleaning steel substrates, indicating the capabilities of each in attaining specified levels of cleanliness.
These International Standards do not contain provisions on the protective coating systems applied
to the steel surface. They do not contain provisions related to the surface quality requirements for
specific situations even though surface quality can have a direct influence on the choice of protective
coating applied and on its performance. Such provisions are given in other documents such as national
standards and codes of practice. It would be useful for users of these International Standards to ensure
that the qualities specified are
— compatible and appropriate both for the environmental conditions to which the steel will be exposed
and for the protective coating system used, and
— within the capability of the cleaning procedure specified.
While these four series of International Standards deal with specific aspects of the preparation of steel
substrates, the ISO 8501 series covers the visual assessment of surface cleanliness.
ISO 8501-1 is intended to be a tool for visual assessment of rust grades and of preparation grades. It
identifies four levels (designated as “rust grades”) of mill scale and rust that are commonly found on
surfaces of uncoated erected steel and steel held in stock. It also identifies certain degrees of visual
cleanliness (designated as “preparation grades”) after surface preparation of uncoated steel surfaces
and of steel surfaces after overall removal of any previous coating. These levels of visual cleanliness are
related to the common methods of surface cleaning that are used prior to painting.
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TECHNICAL REPORT ISO/TR 22770:2019(E)
Preparation of steel substrates before application of paints
and related products — Analytical colorimetry method to
support visual assessment of surface preparation grades
1 Scope
This document provides guidance on the usage of analytical colorimetry to support visual assessment
of surface preparation grades described in ISO 8501-1:2007, Clause 4.
This document provides examples of applications where the use of a colorimeter or spectrophotometer
can enable a quick and objective assessment of the preparation grade of the substrate.
NOTE The data given in this document was obtained using the methodology described in Annex A.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 8501-1, Preparation of steel substrates before application of paints and related products — Visual
assessment of surface cleanliness — Part 1: Rust grades and preparation grades of uncoated steel substrates
and of steel substrates after overall removal of previous coatings
3 Terms and definitions
For the purposes of this document, the terms and definitions given in in ISO 8501-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
CIELAB colour space
CIE 1976 L* a* b* colour space
three-dimensional L *, a*, b* colour space
3.2
colour difference
difference between two colour stimuli defined as the Euclidean distance between the points
representing them in the L* a* b* space and calculated as follows
2 2 2 1/2
ΔE* = [(ΔL*) + (Δa*) + (Δb*) ]
3.3
illuminant
radiation with a relative spectral power distribution defined over the wavelength range that influences
object colour perception
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ISO/TR 22770:2019(E)

3.4
standard illuminant
illuminants (3.3) by the CIE defined in terms of relative spectral power distributions
Note 1 to entry: These illuminants are intended to represent the following:
a) Planckian radiation at a temperature of about 2 856 K;
b) direct solar radiation (obsolete);
c) average daylight;
d) daylight.
The 2-digit number associated to D illuminant denotes the correlated colour temperature.
3.5
observer
CIE 1931 standard colorimetric observer
ideal observer whose colour-matching properties correspond to the CIE colour-matching functions
adopted by the CIE in 1931
Note 1 to entry: This standard colorimetric system is applicable to centrally-viewed fields of angular subtending
between about 1° and about 4°.
3.6
supplementary standardized observer
CIE 1964 supplementary standard colorimetric observer
ideal observer whose colour-matching properties correspond to the CIE colour-matching functions
adopted by the CIE in 1964
Note 1 to entry: This standard colorimetric system is applicable to centrally-viewed fields of angular subtense
greater than about 4°.
Note 2 to entry: When this system is used, all symbols that represent colorimetric measures are distinguished by
use of the subscript 10.
4 Symbols
L* CIELAB lightness
a*, b* CIELAB a*, b* coordinates
ΔL* CIELAB lightness difference
Δa*, Δb* CIELAB a*, b* difference
ΔE* CIELAB colour difference
ΔC* CIELAB chroma difference
ΔH* CIELAB hue difference
5 Principle
The assessment of preparation grade of the surface is done by calculation of the colour difference
components, taking as reference the colour components values of a substrate with the targeted surface
preparation grade.
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ISO/TR 22770:2019(E)

The surface preparation will be considered as acceptable if the colour difference is below a certain
...