ISO 21746:2019

INTERNATIONAL ISO
STANDARD 21746
First edition
2019-04
Composites and metal assemblies —
Galvanic corrosion tests of carbon
fibre reinforced plastics (CFRPs)
related bonded or fastened
structures in artificial atmospheres
— Salt spray tests
Assemblages composites et métal — Essais de corrosion galvanique des
structures en plastiques renforcés de fibres de carbone (CFRP) jointes
ou fixées en atmosphères artificielles — Essais au brouillard salin
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test solutions . 2
4.1 Preparation of the sodium chloride solution . 2
4.2 pH adjustment . 3
4.2.1 pH of the salt solution . 3
4.2.2 Neutral salt spray test (NSS) . 3
4.2.3 Acetic acid salt spray test (AASS) . 3
4.2.4 Copper-accelerated acetic acid salt spray test (CASS) . 3
4.3 Filtration . 3
5 Apparatus . 4
6 Method for evaluating cabinet corrosivity . 5
6.1 General . 5
6.2 Reference specimens . 5
6.3 Arrangement of the reference specimens. 6
6.4 Duration of tests . 6
6.5 Determination of mass loss (mass per area) . 6
6.6 Satisfactory performance of cabinet . 6
7 Test specimens. 7
8 Arrangement of the test specimens . 7
9 Operating conditions . 8
10 Duration of tests . 8
11 Treatment of specimens after test . 9
11.1 General . 9
11.2 Non-organic coated specimens: metallic and/or inorganic coated . 9
11.3 Organic coated specimens . 9
11.3.1 Scribed organic coated specimens . 9
11.3.2 Organic coated but not scribed specimens . 9
12 Evaluation of results . 9
13 Test report .10
Annex A (informative) Example schematic diagram of one possible design of spray cabinet
for galvanic corrosion test with means for optional treating fog exhaust and drain .11
Annex B (informative) Complementary method for evaluating galvanic corrosion test
cabinet corrosivity using zinc reference specimens .13
Annex C (normative) Preparation of galvanic corrosion test panels with organic coatings .15
Annex D (normative) Required supplementary information for testing galvanic corrosion
test panels with organic coatings .16
Annex E (informative) Recommended specimen geometries — Salt spray tests to metal and
CFRP assemblies .17
Bibliography .19
Foreword
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This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 13,
Composites and reinforcement fibres.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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iv © ISO 2019 – All rights reserved

Introduction
This document specifies the testing method for galvanic corrosion of composites and metal assemblies
subject to salt spray environment using a bonded or fastened specimen.
The potential benefits to CFRP-metal users of implementing a galvanic corrosion test based on this
document are:
a) addressing corrosion risks relating CFRPs of drastically nobler galvanic potential than metals to
form a global cell between CFRP and metal – new risks drastically exceeding the scope of ISO 9227
for a local cell of isolated metal – utilizing the resources of ISO 9227;
b) expanding CFRP applications to the fields of corrosive environments that still require the
combinations with metallic components;
c) the detection or the prevention of galvanic current insulation loss, such as ion migration and
time-related degradation in sealant film, injected calking layer and glass fibre reinforced plastics
(GFRPs) layer;
d) demonstrating the conformity to specified conditions for type certification requirements in the
engineering such as aircraft developments;
e) evaluating the corrosion related procedures for maintenance, repair and overhaul (MRO) in the
engineering operations such of CFRP aircrafts.
It is not the intent of this document to imply the need for:
— omitting relevant field tests for CFRP related engineering;
— generally specifying the dimensions of test specimen to represent CFRPs related bonded or fastened
structures;
— superimposing test results for specific applications of the parameters that exceed the range of this
document;
— comparative testing as a means of ranking different protections with respect to corrosion resistance.
INTERNATIONAL STANDARD ISO 21746:2019(E)
Composites and metal assemblies — Galvanic corrosion
tests of carbon fibre reinforced plastics (CFRPs) related
bonded or fastened structures in artificial atmospheres —
Salt spray tests
1 Scope
This document specifies the apparatus, the reagents and the procedure to be used in conducting the
neutral salt spray (NSS), acetic acid salt spray (AASS) and copper-accelerated acetic acid salt spray
(CASS) tests for assessment of the galvanic corrosion resistance of joints and bonded structures
between carbon fibre reinforced plastics (CFRPs) and metallic materials, with or without permanent or
temporary insulation for the galvanic current.
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 1514, Paints and varnishes — Standard panels for testing
ISO 2808, Paints and varnishes — Determination of film thickness
ISO 3574, Cold-reduced carbon steel sheet of commercial and drawing qualities
ISO 6361-2, Wrought aluminium and aluminium alloys — Sheets, strips and plates — Part 2: Mechanical
properties
ISO 8044, Corrosion of metals and alloys — Basic terms and definitions
ISO 8407, Corrosion of metals and alloys — Removal of corrosion products from corrosion test specimens
ISO 17872, Paints and varnishes — Guidelines for the introduction of scribe marks through coatings on
metallic panels for corrosion testing
3 Terms and definitions
For
...