ISO 8057:2024

International
Standard
ISO 8057
First edition
Determination of galvanic corrosion
2024-01
rate for assembled forms of carbon
fibre reinforced plastics (CFRPs)
and protection-coated metal —
Electrochemical tests in neutral
sodium chloride solution
Détermination du taux de corrosion galvanique pour les formes
assemblées de plastiques renforcés de fibres de carbone (CFRP)
et de métal revêtu de protection — Essais électrochimiques en
solution neutre de chlorure de sodium
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 2
5 Principle . 3
5.1 General .3
5.2 Capacitor model .3
5.3 Fick’s diffusion coefficient for thin coating layer .4
5.4 Corrosion rate estimation .6
6 Test solutions . 7
7 Apparatus . 8
7.1 Potentio/Galvanostat .8
7.2 Test cell .8
8 Test specimen preparation . 9
9 Test procedure . 9
9.1 Fick’s diffusion parameter — Setups .9
9.2 Fick’s diffusion parameter — Calculation .10
9.3 Corrosion rate estimation .11
10 Test report .11
Annex A (informative) Example of measurement for Fick’s diffusion parameter .12

iii
Foreword
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iv
International Standard ISO 8057:2024(en)
Determination of galvanic corrosion rate for assembled forms
of carbon fibre reinforced plastics (CFRPs) and protection-
coated metal — Electrochemical tests in neutral sodium
chloride solution
1 Scope
1.1 This document specifies the electrochemical test for determining galvanic corrosion rate of CFRPs and
metal assemblies with protection-coating, subjected to the corrosive environment of electrolyte diffusion
through the coating. It specifies the apparatus, the test solutions, and the procedure to be used in conducting
the electrochemical tests for
a) the assessment of the Fick's diffusion parameter for protective coating on metallic materials, and
b) the estimation of the galvanic corrosion rates with the conversion of ISO 21746 coating-free sample
data.
1.2 The following are intended situations of implementing an electrochemical test based on this document:
a) when interested parties estimate the galvanic corrosion rate of bonded joints relating engineering
metals with protection-coating and CFRPs of the potential drastically nobler than those of most metals,
utilizing the resources of ISO 17475;
b) when expanding CFRP-metal bonded joints applications using coatings to the fields of corrosion-
sensitive environments caused by electrolytes.
1.3 It is not the intent of this document to fulfil the need for:
— omitting relevant field tests for the applications in corrosive environment;
— superimposing test data for specific applications for the range of relevant data;
— comparative testing as a means of ranking different protections with respect to corrosion rates;
— ignoring the field hazards such as erosion, abrasion, and ultraviolet irradiation.
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 2808, Paints and varnishes — Determination of film thickness
ISO 17475, Corrosion of metals and alloys — Electrochemical test methods — Guidelines for conducting
potentiostatic and potentiodynamic polarization measurements
ISO 21746, Composites and metal assemblies — Galvanic corrosion tests of carbon fibre reinforced plastics
(CFRPs) related bonded or fastened structures in artificial atmospheres — Salt spray tests

3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Symbols
a slope of Q-t plot
b error in Q-t plot owing to charge duration and other factors
C static capacity of capacitor
c saturated oxygen density in water
O
c(x) electrolyte density function
d coating thickness
D Fick’s diffusion parameter
D oxygen diffusion constant in water
ox
E estimation of galvanic corrosion rate for coated sample
cr
F protection efficiency
pe
J diffusion flux
J oxygen flux in air saturated static water
ASO
J steady flux through thin protective coating
PC
J oxygen flux through protection coating
PCO
J oxygen flux of air saturated water for protection free sample
PFO
J the maximum through coating flux of oxygen in the form of water solution
OMax
K galvanic corrosion rate of coating-free sample derived with ISO 21746
cr
Q charge at a time t
Q charge at linearly extrapolated time point t
0 0
S grid area of capacitor
t time
t flux onset time
t upper bound time of linear section in time-charge plot
V inter-grid potential of capacitor
x inter-grid distance of capacitor
x locational dimension in flux direction
x diffusion layer thickness
DL
ε
permittivity of vacuum
ε
relative permittivity
r
5 Principle
5.1 General
Protection coating behaves as a capacitor in the form between conductive materials and conductive
electrolytes. Focusing on the capacitance, Fick's diffusion parameter is monitored by analysing the drift in
charge due to the distance shrinkage with electrolyte absorption from the surface of the protective coating
in the plate-shaped sample. The effect of the protective coating is evaluated by converting the value into the
salt spray flux in the galvanic corrosion test.
5.2 Capacitor model
Static capacity, C, of a capacitor in Figure 1 is expressed as Formula (1):
S
C =εε (1)
r 0
x
−12
whereε =×8,85418762 10 is the permittivity of vacuum.
The charge, Q, is expressed as follows when inter-grid potential, V, is loaded.
QC= V (2)
Formulae (1) and (2) lead to the following expression.
SV
Q=εε (3)
r 0
x
When the inter-grid distance x shrinks to x -Δx through diffusion, the charge drift ΔQ is expressed using
1 1 1
Formula (3) as follows.
xQΔΔ+=Qx 0 (4)
Figure 1 — Schematic diagram of capacitor
A capacitor in Figure 1 is expressed as is shown in Figure 2 for a grid of conductive base material, a grid of
electrolyte, and thin coating with the thickness, x , to separate the grids.
Key
1 water/electrolyte
2 thin coating layer
3 conductive base
Figure 2 — Capacitor formation with thin coating layer
5.3 Fick’s diffusion coefficient for thin coating layer
A. Fick expressed the phenomenon of water diffusion in a mathematical form using an analogy with the
...