ISO 23721:2022

INTERNATIONAL ISO
STANDARD 23721
First edition
2022-03
Corrosion of metals and alloys —
Rating method by appearance of rust
and stains of atmospheric corrosion
for stainless steels
Corrosion des métaux et alliages — Méthode de cotation par
l'apparence de la rouille et des taches de corrosion atmosphérique
pour les aciers inoxydables
Reference number
© ISO 2022
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
4.1 Photographic standard. 1
4.2 Rating method . . . 11
5 Expression of results .12
6 Test report .12
Annex A (informative) Relationship between rating number and total area of rust and
stains .13
Bibliography .14
iii
Foreword
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iv
Introduction
Stainless steels contain at least 10,5 % Cr and are widely used in domestic electric utilities, kitchen
utensils, transportation vehicles, and industrial plants. Corrosion-resistant stainless steels are also
used as architectural materials, e.g. exterior parts and roofs of buildings. Furthermore, stainless steels
are used as braid materials for automotive parts.
Corrosion loss and pitting depth are important factors for selecting, deciding the thickness and
estimating the lifetime of materials. Aesthetic appearance is also important for stainless steels used in
exterior parts. Therefore, a method for evaluating the appearance of stainless steels under atmospheric
exposure is required.
v
INTERNATIONAL STANDARD ISO 23721:2022(E)
Corrosion of metals and alloys — Rating method by
appearance of rust and stains of atmospheric corrosion for
stainless steels
1 Scope
This document specifies a method for evaluating the aesthetic app
...