ISO 23721:2022

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 23721
ISO/TC 156
Corrosion of metals and alloys —
Secretariat: SAC
Rating method by appearance of rust
Voting begins on:
2021-12-13 and stains of atmospheric corrosion
for stainless steels
Voting terminates on:
2022-02-07
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 23721:2021(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2021

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ISO/FDIS 23721:2021(E)
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© ISO 2021
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ISO/FDIS 23721:2021(E)
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
© ISO 2021 – All rights reserved

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ISO/FDIS 23721:2021(E)
Foreword
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
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described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
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This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
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/FDIS 23721:2021(E)
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.
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© ISO 2021 – All rights reserved

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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 23721:2021(E)
Corrosio
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