ISO 19691

• Abstract:

  This international standard specifies a method for measuring the corrosion loss of each part of structures using unpainted steel such as weathering steel by using the attached coupons Also this standard provides a prediction method for corrosion loss over a long period from the measurement results and a method for determining the applicability of existing and new constructing weathering steel structures. Also this standard provides a method for evaluating the type of corrosion by visual inspection of the appearance of rust on an existing weathering steel structure.

• Status: Not Published
• ICS: 77.060 - Corrosion of metals
• ICS: 91.080.13 - Steel structures
• Technical Committee: ISO/TC 156 - Corrosion of metals and alloys
• Drafting Committee: ISO/TC 156 - Corrosion of metals and alloys
• Current Stage: 6000 - International Standard under publication
• Start Date: 27-Jun-2026
• Completion Date: 29-Aug-2026

Overview

ISO 19691: Measurement method of corrosion for weathering steel structures is an international standard developed by ISO that outlines a systematic approach for assessing corrosion in unpainted steel structures, such as those made from weathering steel. The standard specifies the use of attached coupons to measure corrosion loss on various parts of steel structures. In addition to quantifying corrosion, ISO 19691 offers methodologies for predicting long-term corrosion loss, evaluating the applicability of weathering steel for both existing and new structures, and visually inspecting corrosion types based on rust appearance.

Key Topics

• Corrosion Measurement Using Coupons:
  The core method defined in ISO 19691 involves attaching standardized steel coupons directly to structure components. These coupons, made of the same material as the structure, are exposed for set periods and later analyzed for mass loss to determine corrosion rates.

• Exposure Test Method:
  The document covers:

  • Coupon specifications (size, thickness, material),
  • Proper installation techniques (using adhesive tape, mechanical fasteners, or wires),
  • Specific guidance on positioning coupons based on environmental and microclimate factors.

• Evaluation and Data Interpretation:
  After exposure, the procedure for cleaning, weighing, and assessing coupons is detailed, following referenced standards such as ISO 8407 for rust removal. Photography is used to document coupon appearance before cleaning.

• Long-term Corrosion Prediction:
  Procedures for predicting corrosion loss over several years are provided, using regression formulas to enable reliable maintenance and design planning.

• Suitability Assessment:
  The standard includes a methodology for determining whether weathering steel is appropriate for new or existing applications, taking into account performance requirements and site-specific environmental data.

• Visual Rust Inspection:
  Guidelines for identifying types of corrosion visually are included to complement quantitative measurements.

Applications

ISO 19691 finds significant practical value in various industries and scenarios, particularly in:

• Bridge and Infrastructure Maintenance:
  Enables engineers to accurately monitor weathering steel corrosion, schedule timely maintenance, and prevent structural failures due to material degradation.
• Design of New Steel Structures:
  Offers a scientific method for evaluating the viability of weathering steel in new construction projects, enhancing durability and cost-effectiveness.
• Asset Management:
  Improves lifecycle management for steel structures by providing data-driven corrosion predictions and insights into environmental suitability.
• Quality Assurance:
  Facilitates objective, standardized assessments required for regulatory compliance and quality control.

By following ISO 19691, organizations ensure consistent and reproducible corrosion assessment across different climates and structure types. The use of standardized coupons and reporting procedures leads to comparable results, supporting global best practices in corrosion management.

Related Standards

ISO 19691 references and complements several other ISO standards for corrosion and atmospheric effects on metals, including:

• ISO 8407:Corrosion of metals and alloys - Removal of corrosion products from corrosion test specimens.
• ISO 9223:Corrosion of metals and alloys - Corrosivity of atmospheres - Classification, determination, and estimation.
• ISO 9224:Corrosion of metals and alloys - Corrosivity of atmospheres - Guiding values for the corrosivity categories.
• ISO 22410:Corrosion of metals and alloys - Electrochemical measurement of ion transfer resistance to characterize the protective rust layer on weathering steel.

Summary

ISO 19691 is an essential standard for the assessment and prediction of corrosion in unpainted weathering steel structures. Its methodologies enhance structural integrity, promote effective maintenance programs, and support the sustainable application of weathering steel in infrastructure and construction. Compliance with this international standard ensures reliable corrosion management and aligns practices with global industry benchmarks.

DRAFT
International
Standard
ISO/DIS 19691
ISO/TC 156
Measurement method of corrosion
Secretariat: SAC
for weathering steel structures
Voting begins on:
ICS: 77.060; 91.080.13
2025-03-07
Voting terminates on:
2025-05-30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
This document is circulated as received from the committee secretariat.
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
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 SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 19691:2025(en)
DRAFT
ISO/DIS 19691:2025(en)
International
Standard
ISO/DIS 19691
ISO/TC 156
Measurement method of corrosion
Secretariat: SAC
for weathering steel structures
Voting begins on:
ICS: 77.060; 91.080.13
Voting terminates on:
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
This document is circulated as received from the committee secretariat. BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 19691:2025(en)
ii
ISO/DIS 19691:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Object . 1
5 Exposure test method . 2
5.1 Shape of coupon .2
5.2 Installation .2
5.3 Installation part .3
5.4 Exposure period .3
6 Evaluation methods . 4
6.1 Documentation of coupon appearance .4
6.2 Method of removing corrosion product on coupon surface .4
6.3 Calculation of corrosion loss .4
6.4 Prediction method.5
7 Electrochemical measurement of ion transfer resistance to characterize the protective
rust layer on weathering steel . 5
8 Report . 5
Annex A (informative) a prediction method for corrosion loss over a long period from the
measurement results and a method for determining the applicability of existing and
new constructing weathering steel structures. . 6
Bibliography . 9

iii
ISO/DIS 19691:2025(en)
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 [or Project Committee] ISO/TC [or ISO/PC] 156,
Atmospheric corrosion testing classification of corrosivity of atmosphere
A list of all parts in the ISO ##### series can be found on the ISO website.
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.

iv
ISO/DIS 19691:2025(en)
Introduction
Weathering steels are environmentally friendly steels that are used in structures without painting. For
example, weathering steel is often used in bridges in mountainous areas in the world. In structural steels,
reduction of the cross section of members due to corrosion can cause deformation and buckling and thus
fracture. For this reason, it is important to understand the corrosion behaviour of each part of structural
members.
Corrosion depends on the microclimate of each part of a member. For example, corrosion is affected by
whether the member is directly exposed to rainfall, whether its surface is horizontal or vertical, how much
de-icing salt is applied, etc.
In the outdoor exposure test using a normal rack of ISO 8565, there is a problem that the corrosion behaviour
of the individual parts of complicated structures cannot be evaluated. Although evaluation is possible by
using a simulation or the actual structure, coring samples cannot be evaluated by weight loss. A method
using a depth gauge and ultrasonic waves is also possible, but has low accuracy for thickness reduction.
To solve the problems mentioned above, a unique exposure test method, in which small steel coupons are
attached to the target parts of members of the actual structure has been studied. This method makes it
possible to measure the corrosion loss on only one side of the members of the structure. It is useful for
making decisions regarding the timing of maintenance, or whether a new structure should be constructed
at the site.
This standard is useful and effective for the security of structures worldwide.

v
DRAFT International Standard ISO/DIS 19691:2025(en)
Measurement method of corrosion for weathering steel
structures
1 Scope
This international standard specifies a method for measuring the corrosion loss of each part of structures
using unpainted steel such as weathering steel by using the attached coupons
Also this standard provides a prediction method for corrosion loss over a long period from the measurement
results and a method for determining the applicability of existing and new constructing weathering steel
structures.
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 8407, Corrosion of metals and alloys — Removal of corrosion products from corrosion test specimens
ISO 9223, Corrosion of metals and alloys — Corrosivity of atmospheres — Classification, determination and
estimation
ISO 9224, Corrosion of metals and alloys — Corrosivity of atmospheres — Guiding values for the corrosivity
categories
ISO 9226, Corrosion of metals and alloys — Corrosivity of atmospheres — Determination of corrosion rate of
standard specimens for the evaluation of corrosivity
ISO 22410, Corrosion of metals and alloys — Electrochemical measurement of ion transfer resistance to
characterize the protective rust layer on weathering steel
ISO 8565, Metals and alloys — Atmospheric corrosion testing — General requirements
3 Terms and definitions
3.1
Weathering steel
Weathering steel containing Cu, Ni, P, etc., is widely used for bridges, buildings, towers and other large
structures because of its low maintenance characteristics resulting from the formation of a protective and
adhesive rust layer when exposed to the atmosphere.
4 Object
The object of measurement of corrosion loss by this test is large structures with specific microclimate
for different elements and/or surfaces. The material of the object structures is uncoated steel, such as
weathering steel to which a corrosion protective covering is not applied, and is limited to cases that take the
form of general corrosion.
ISO/DIS 19691:2025(en)
5 Exposure test method
5.1 Shape of coupon
The coupon structure shall be as follows.
a) The standard shape of the coupon is square with a one-side length of 50 mm as shown in Figure 1.
However, square coupons with a one-side length of 40 mm to 150 mm may also be used, provided it is
possible to secure the accuracy of mass measurements.
b) The standard thickness of the coupon is 2 mm. Thicknesses in the range of 1,5 mm to 3 mm should also
be used
...

FINAL DRAFT
International
Standard
ISO/FDIS 19691
ISO/TC 156
Measurement method of corrosion
Secretariat: SAC
for weathering steel structures
Voting begins on:
2026-05-01
Voting terminates on:
2026-06-26
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
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
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.
Reference number
ISO/FDIS 19691:2026(en) © ISO 2026

FINAL DRAFT
ISO/FDIS 19691:2026(en)
International
Standard
ISO/FDIS 19691
ISO/TC 156
Measurement method of corrosion
Secretariat: SAC
for weathering steel structures
Voting begins on:
Voting terminates on:
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.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 19691:2026(en) © ISO 2026

ii
ISO/FDIS 19691:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Object . 1
5 Exposure test method . 1
5.1 Shape of coupon .1
5.2 Installation .2
5.3 Installation part .4
5.4 Exposure period .4
6 Evaluation methods . 4
6.1 General .4
6.2 Documentation of coupon appearance .4
6.3 Method of removing corrosion product on coupon surface .5
6.4 Calculation of corrosion loss .5
6.5 Prediction method.5
7 Electrochemical measurement of ion transfer resistance to characterize the protective
rust layer on weathering steel . 5
8 Test report . 5
Annex A (informative) Prediction method for long term corrosion loss and determining the
applicability of weathering steel structures . 7
Bibliography .10

iii
ISO/FDIS 19691:2026(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 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.

iv
ISO/FDIS 19691:2026(en)
Introduction
Weathering steels are environmentally friendly steels that are used in structures without painting. For
example, weathering steel is often used in bridges in mountainous areas in the world. In structural steels,
reduction of the cross section of members due to corrosion can cause deformation and buckling and thus
fracture. For this reason, it is important to understand the corrosion behaviour of each part of the structural
members.
Corrosion depends on the microclimate of each part of a member. For example, corrosion is affected by
whether the member is directly exposed to rainfall, whether its surface is horizontal or vertical, how much
de-icing salt is applied, etc.
In the outdoor exposure test using a normal rack, the corrosion behaviour of the individual parts of
complicated structures cannot be evaluated. Although evaluation is possible by using a simulation or the
actual structure, coring samples cannot be evaluated by weight loss. A method using a depth gauge and
ultrasonic waves is also possible but has low accuracy for thickness reduction.
To solve these problems, a unique exposure test method, in which small steel coupons are attached to the
target parts of members of the actual structure, has been established. This method makes it possible to
measure the corrosion loss on only one side of the members of the structure. It is useful for making decisions
regarding the timing of maintenance, or whether a new structure should be constructed at the site.
This document is useful and effective for the security of structures worldwide.

v
FINAL DRAFT International Standard ISO/FDIS 19691:2026(en)
Measurement method of corrosion for weathering steel
structures
1 Scope
This document specifies a method for measuring the corrosion loss of each part of structures using
unpainted steel such as weathering steel by using the attached coupons.
This document also provides a prediction method for corrosion loss over a long period from the measurement
results and a method for determining the applicability of existing and new constructing weathering steel
structures.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
weathering steel
low-maintenance steel widely used for large structures
Note 1 to entry: Weathering steel typically contains Cu and Ni. It is widely used for large structures like
bridges, buildings and towers.
Note 2 to entry: This type of steel is low maintenance because a protective and adhesive rust layer forms
when exposed to the atmosphere.
4 Object
For this test, the object of measurement of corrosion loss is large structures with specific microclimates
for either different elements or different surfaces or both. The material of the object structures is uncoated
steel, such as weathering steel, to which a corrosion protective covering is not applied and is limited to cases
that take the form of general corrosion.
5 Exposure test method
5.1 Shape of coupon
The coupon structure shall be as follows:
a) The standard shape of the coupon is square with a one-side length of 50 mm as shown in Figure 1.
However, square coupons with a one-side length of 40 mm to 150 mm may also be used, provided it is
possible to secure the accuracy of mass measurements.

ISO/FDIS 19691:2026(en)
b) The standard thickness of the coupon is 2 mm. Thicknesses in the range of 1,5 mm to 3 mm should be
used.
c) The edges of the coupon shall be chamfered.
d) The material of the coupon shall be the steel material which the formula evaluated. To evaluate corrosion
of each part of the structure, the test coupons should be made of the same alloys of the structure
material.
e) The coupon number shall be marked on the adhesive side of the coupon. Mechanical finishing of both
the front and back of the exposed side should be performed.
Key
1 test piece
2 chamfer
3 exposed side
4 back side
Figure 1 — Standard shape and specifications of test piece
5.2 Installation
The coupon shall be attached as follows:
a) The standard coupon attachment method is shown in Figure 2. Dust shall be removed from the surface
to which the coupon is to be attached, and the coupon shall be attached using double-sided adhesive
tape as the standard method.
b) The double-sided tape shall have sufficient adhesion and durability so that the coupon does not detach
during the exposure period. If an exposure period of 5 or more years is applicable, the panels should be
checked at least every year. Make use of a fa
...

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ISO/TC 156
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Secretariat: SAC
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Date: 2025-122026-04-15
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St l D fi iti
ISO/FDIS 19691:2026(en)
Formatted: Font: Bold
Formatted: HeaderCentered
Formatted: Default Paragraph Font
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
Formatted: Right: 1.5 cm, Bottom: 1 cm, Gutter: 0 cm,
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
Header distance from edge: 1.27 cm, Footer distance
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
from edge: 0.5 cm
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Formatted: French (Switzerland)
EmailE-mail: [e-mail]
Formatted: French (Switzerland)
Website: www.iso.orgwww.iso.org
Formatted: French (Switzerland)
Published in Switzerland
Formatted: Font: 10 pt
Formatted: Font: 10 pt
Formatted: Font: 11 pt
Formatted: FooterPageRomanNumber, Space After: 0
pt, Line spacing: single
ii © ISO #### 2026 – All rights reserved
ii
ISO/FDIS 19691:20252026(en)
Formatted: Font: Bold
Formatted: Font: Bold, English (United Kingdom)
Formatted: Font: Bold
Contents
Formatted: Font: Bold
Formatted: HeaderCentered, Left
Foreword . v
Formatted: Adjust space between Latin and Asian text,
Introduction . vi
Adjust space between Asian text and numbers
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Object . 2
5 Exposure test method . 2
5.1 Shape of coupon. 2
5.2 Installation . 3
5.3 Installation part . 5
5.4 Exposure period . 6
6 Evaluation methods . 6
6.1 General. 6
6.2 Documentation of coupon appearance . 6
6.3 Method of removing corrosion product on coupon surface . 7
6.4 Calculation of corrosion loss. 7
6.5 Prediction method . 8
7 Electrochemical measurement of ion transfer resistance to characterize the protective
rust layer on weathering steel . 8
8 Test report . 8
Annex A (informative) Prediction method for long term corrosion loss and determining the
applicability of weathering steel structures . 10
Bibliography . 13

Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references  . 1
3 Terms and definitions . 1
4 Object . 1
5 Exposure test method . 1
6 Evaluation methods . 4
7 Report . 5
Annex A (informative) Annex title e.g. Example of a figure and a table . 7
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A.1 Method for prediction of corrosion loss . 7
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A.1.1 Regression equation . 7
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A.1.2 Number of data (exposure period) . 7
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A.2 Method for selecting coupon attachment positions . 8 Formatted: Font: 11 pt
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A.2.1 When the purpose is partial evaluation of the structure . 8
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iii
ISO/FDIS 19691:2026(en)
Formatted: Font: Bold
Formatted: HeaderCentered
A.2.2 When the purpose is overall evaluation of the structure . 8
A.3 Corrosion prediction method for newly-constructed structures . 8
A.3.1 When a nearby existing structure can be used . 8
A.3.2 When a nearby existing structure cannot be used . 8
A.4 Method for determination of the suitability of the structure . 9
A.4.1 Determination based on required performance . 9
A.4.2 Determination based on the corrosion environment . 9
Bibliography . 10
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iv © ISO #### 2026 – All rights reserved
iv
ISO/FDIS 19691:20252026(en)
Formatted: Font: Bold
Formatted: Font: Bold, English (United Kingdom)
Formatted: Font: Bold
Foreword
Formatted: Font: Bold
ISO (the International Organization for Standardization) is a worldwide federation of national standards
Formatted: HeaderCentered, Left
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
Formatted: Adjust space between Latin and Asian text,
ISO technical committees. Each member body interested in a subject for which a technical committee has been
Adjust space between Asian text and numbers
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 document should be noted. This document was drafted in accordance with the editorial rules of the
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This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
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v
ISO/FDIS 19691:2026(en)
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Introduction
Weathering steels are environmentally friendly steels that are used in structures without painting. For
example, weathering steel is often used in bridges in mountainous areas in the world. In structural steels,
reduction of the cross section of members due to corrosion can cause deformation and buckling and thus
fracture. For this reason, it is important to understand the corrosion behaviour of each part of the structural
members.
Corrosion depends on the microclimate of each part of a member. For example, corrosion is affected by
whether the member is directly exposed to rainfall, whether its surface is horizontal or vertical, how much de-
icing salt is applied, etc.
In the outdoor exposure test using a normal rack , there is a problem that, the corrosion behaviour of the
individual parts of complicated structures cannot be evaluated. Although evaluation is possible by using a
simulation or the actual structure, coring samples cannot be evaluated by weight loss. A method using a depth
gauge and ultrasonic waves is also possible but has low accuracy for thickness reduction.
To solve these problems, a unique exposure test method, in which small steel coupons are attached to the
target parts of members of the actual structure, has been established. This method makes it possible to
measure the corrosion loss on only one side of the members of the structure. It is useful for making decisions
regarding the timing of maintenance, or whether a new structure should be constructed at the site.
This document is useful and effective for the security of structures worldwide.
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vi © ISO #### 2026 – All rights reserved
vi
DRAFT International Standard ISO/DIS 19691:2025(en)

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Measurement method of corrosion for weathering steel structures
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1 Scope
Header distance from edge: 1.27 cm, Footer distance
from edge: 0.5 cm
This document specifies a method for measuring the corrosion loss of each part of structures using unpainted
steel such as weathering steel by using the attached coupons.
This document also provides a prediction method for corrosion loss over a long period from the measurement
results and a method for determining the applicability of existing and new constructing weathering steel
structures.
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 8407, Corrosion of metals and alloys — Removal of corrosion products from corrosion test specimens
ISO 9223, Corrosion of metals and alloys — Corrosivity of atmospheres — Classification, determination and
estimation
ISO 9224, Corrosion of metals and alloys — Corrosivity of atmospheres — Guiding values for the corrosivity
categories
ISO 22410, Corrosion of metals and alloys — Electrochemical measurement of ion transfer resistance to
characterize the protective rust layer on weathering steel
There are no normative references in this document.
3 Terms and definitions Formatted: Adjust space between Latin and Asian text,
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For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
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— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
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— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
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3.1 3.1
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weathering steel
and Asian text, Adjust space between Asian text and
low-maintenance steel widely used for large structures numbers
Note 1 to entry: Weathering steel containingtypically contains Cu, and Ni.,. It is widely used for large structures
like bridges, buildings, and towers and other large structures.
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Note 2 to entry: This type of steel is low maintenance because of its low maintenance characteristics resulting
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from the formation of a protective and adhesive rust layer forms when exposed to the atmosphere.
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ISO/FDIS 19691:2026(en)
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4 Object
TheFor this test, the object of measurement of corrosion loss by this test is large structures with specific
microclimatemicroclimates for either different elements or different surfaces, or both. The material of the
object structures is uncoated steel, such as weathering steel, to which a corrosion protective covering is not
applied and is limited to cases that take the form of general corrosion.
5 Exposure test method
5.1 Shape of coupon
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The coupon structure shall be as follows:
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a) a) The standard shape of the coupon is square with a one-side length of 50 mm as shown in
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Figure 1.Figure 1. However, square coupons with a one-side length of 40 mm to 150 mm may also be used,
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provided it is possible to secure the accuracy of mass measurements.
b, c, … + Start at: 1 + Alignment: Left + Aligned at: 0
cm + Indent at: 0 cm, Adjust space between Latin and
b) b) The standard thickness of the coupon is 2 mm. Thicknesses in the range of 1,5 mm to 3 mm
Asian text, Adjust space between Asian text and
should also be used if necessary.
numbers
c) c) The edges of the coupon are toshall be chamfered.
d) d) The material of the coupon shall be the steel material which the formula evaluated. To evaluate
corrosion of each part of the structure, the test coupons should be made of the same alloys of the structure
material.
e) e) The coupon number shall be marked on the adhesive side of the coupon. Mechanical finishing
of both the front and back of the exposed side should be performed.

50 2
2 2
3 4
(unit : mm)
2 2
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Key
1 test piece
2 chanfer
3 exposed side
4 back side
1 test piece
2 chamfer
3 exposed side
4 back side
Figure 1 — Standard shape and specifications of test piece.
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Asian text, Adjust space between Asian text and
numbers
5.2 Installation
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The method of attaching the coupon shall be attached as follows: Adjust space between Asian text and numbers, Tab
stops: Not at 0.71 cm
a) a) The standard coupon attachment method is shown in Figure 2.Figure 2. Dust shall be removed
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from the surface to which the coupon is to be attached, and the coupon is toshall be attached using double-
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sided adhesive tape as the standard method.
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b, c, … + Start at: 1 + Alignment: Left + Aligned at: 0
b) b) The double-sided tape shall have sufficient adhesion and durability so that the coupon does
cm + Indent at: 0 cm, Adjust space between Latin and
not detach during the exposure period. If an exposure period of 5 or more years is applicable, the panels
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should be checked at least every year. Make use of a fall prevention aid, see 5.2,5.2, list item d).
numbers
c) c) The double-sided tape is toshall be set so that it is larger than the dimensions of the coupon.
As a guideline, theThe tape should protrude from the outer periphery of the coupon by approximately
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1 mm.
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d) d) Examples of the condition of coupon installation are shown in Figure 2Figure 2 and
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Figure 3.Figure 3. As shown in Figure 3, in orderFigure 3, to prevent the test pieces from falling and
damaging pedestrians, cars, etc., a method is used in which a hole of about 2 mm ⌀ is made in the sample Formatted: FooterCentered, Left, Space Before: 0 pt,
and a wire is passed through it. Tab stops: Not at 17.2 cm
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ISO/FDIS 19691:2026(en)
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Key
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1 test piece
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2 double-sided tape
3 steel member
4 surface preparation
1 test piece
2 double-sided tape
3 steel member
4 surface preparation
1 1
4 4
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Figure 2 — Method of attaching test piece
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numbers
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Key
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1 test piece
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2 coated wire
3 steel member
4 Nylon thread
1 test piece
2 coated wire Formatted: None, Adjust space between Latin and
Asian text, Adjust space between Asian text and
3 steel member
numbers
4 Nylon thread
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Figure 3 — Outline of test piece attachment
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a) In addition, the following conditions apply:
Asian text and numbers
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1) — Position the hole in the panel so that it is about 5 mm from the edge and the dripping water
Numbering Style: 1, 2, 3, … + Start at: 1 + Alignment:
does not run over the whole panel, see Figure 3.Figure 3.
Left + Aligned at: 0 c
...