Volume 7 Preprint 47
Development of a flash test for fast qualification of the durability of painted galvanised steel sheets used for roofing in equatorial/tropical environment
Jacques Pigerre, Pablo Rodriguez and Jean-Louis Mansot
Keywords: ultrasound, cavitation, wet adhesion
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Volume 7 Paper 47
Development of a flash test for fast qualification
of the durability of painted galvanised steel sheets used for
roofing in equatorial/ tropical environment.
Jacques PIGERRE a, Pablo RODRIGUEZ a and Jean-Louis MANSOT b
Groupe de Technologie des Surfaces et Interfaces (GTSI EA
Université des Antilles et de la Guyane, Institut d’Enseignement
Supérieur de Guyane, aAvenue d’Estrées Campus Saint-Denis BP
792, 97337 Cayenne Cedex, French Guiana, bFaculté des Sciences
Exactes et Naturelles, Campus Fouillole, 97159 Pointe à Pitre
cedex Guadeloupe (France).
characterize the toughness of the paint /metal interface of
manufactured prepainted galvanized steel sheet used for roofing
in the Caribbean area. The morphologies and kinetics of damage
processes of the painted surfaces generated by the ultrasonic
solicitations, are quantitatively followed and correlated to long
term efficiency of the tested anticorrosion treatments.
Keywords : ultrasounds, cavitation, wet adhesion
This is a preprint of a paper that has been submitted for publication in the Journal of Corrosion Science
and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at
http://www.umist.ac.uk/corrosion/jcse in due course. Until such time as it has been fully published it
should not normally be referenced in published work. © UMIST 2004.
Galvanised steel sheets are extensively used in the
Caribbean area for the roofing of houses. Due to the high
aggressiveness of the tropical/equatorial climate, the protection
against corrosion of such materials must be strongly reinforced
in order to increase their durability.
A classical low cost process of protection of non stainless steel
consists of application of galvanization coatings. In order to
reinforce the efficiency and for aesthetic purpose, such
galvanized materials can be covered by various organic coatings
such as paints. These coatings are supposed to enhance the
protection effect by addition of corrosion inhibitors in the
primary layer and to reduce the intrusion of water to the interface
by a barrier effect of the finishing layer.
The main problem which has to be solved is the evaluation of
the durability and/or long term efficiency of such treatments. Up
to now, the classical procedure used to evaluate these properties
is the exposure in severe environmental conditions in order to
accelerate the damage processes. This is done in stands where
UV, moisture, temperature mechanical stresses can be applied
simultaneously in a controlled manner. Such procedures need
however long time experiments (up to ten years in natural
exposure). Some shorter tests (scratch test, friction test, pilling
test…) are also used to evaluate some mechanical or adhesive
properties of the coatings which can have significant influences
on the durability of the materials.
In this work a flash test (few minutes experiment) based on
ultrasonic solicitations is developed  in order to qualify the
adhesion of organic coatings used for corrosion protection of
The behaviour of various samples during the flash test
(stripping kinetic, morphology of the stripping) is deeply
investigated and the quantitative results are correlated to the
long term behaviour of the same samples in natural exposure on
a C5 class stand in Cayenne.
Some relevant quantitative parameters are used in order to
classify long term efficiency of such coatings.
The studied materials are composite coatings made of four
layers deposited on steel substrates as described in the
schematic cross-section presented in figure 1 .
The galvanization treatment, consisting of covering steel
with a zinc-based alloy, is the first protection layer against
corrosion. The second layer enhances the adhesion between the
metal and the organic coating. The first paint layer (primary
layer) is composed of a polymer containing corrosion inhibitors.
The second paint layer (finishing layer) containing pigments and
UV stabilizers operates as a barrier [3-4] to avoid diffusion of
Figure 1 : Schematic representation of the different layers used for the protection of
the steel sheets 
Classical “natural exposure test” for the
qualification of the
system of paint
Pieces of the samples of interest were exposed according to
standard ECCA T19 on the stand located in Cayenne (French
Guyana, figure 2a) during four years from 1998 to 2002. The
environmental stand parameters over one year were readily
stable during the four years of exposure, with a monthly
sunshine light of 200 hours, monthly averages temperatures
between 26 and 28 °C, relative humidity between 82 and 92 %,
annual rainfall of 3000 millimetres mainly between December
and July. These parameters lead to a C5 classification of the
stand according to ISO 9223-1992 .
To enable the classification of the systems of paint, and by
the way to give an image of there durability, a few parameters are
taken into account as it can be seen on figure 2b:
Figure 2 : Natural exposure in Cayenne (French Guiana)
a ) the stand, b ) Typical aspect of a 4 years exposed sample
width of cathodic delamination from the edges, presence or
not of cracks on the folds, paint metal disbondment ...
The test has been developed from published works of J.
SCHULTZ  and H. HAIDARA  on metal thin films (a few
nanometres thick) vapour deposited on polymer substrates.
The conditions of our test are described in figure 3. The
samples are discs of 18 mm diameter obtained by stamping steel
sheets of interest. Each sample is glued on the probe so that the
painted face keeps in contact with the liquid (see figure 4). The
samples are then submitted to ultrasonic solicitations (90W,
20kHz) by sequences of 30 sec to 1 min depending on the
behaviour of the coating. After each sequence, a digitized picture
of the painted surface is recorded. At the end of the test (total
stripping of the paint layers) computerised analyses of the
digitized pictures allow us to quantitatively evaluate the surface
fraction still covered by the paint (non stripped area fraction).
Substrate of sample
Figure 3 : device used for the test using ultrasounds
generator : a) experimental design, b) detail of the
sample during the test
Mechanical effects of ultrasounds
Due to the high velocity of the probe’s tip surface, bubbles
of water vapour appear near the tip as soon as the test runs
(figure 3b). In the same time, whirlpool streams of the liquid
medium take place in the becker [8, 9].
It is well known that ultrasounds make the liquid medium
unstable and produce in a very short time the evaporation of the
liquid into small bubbles (cavitation bubbles) of different sizes. It
has been demonstrated , solving the motion equation of a
bubble frontier in a high powered ultrasound field, that mainly
two kinds of bubbles exist : stationary and transitory cavitation
The stationary cavitation bubbles oscillate in the field of
ultrasounds at there own rhythm. Their volume periodically
varies inducing an alternative pumping effect on the paint able to
initiate disbondment at the paint metal interface (fatigue
phenomenon) and periodic intrusion of water at the interface
(figure 4a, b) . These effects can lead to the stripping of large
flakes (figure 4c) .
The transitory cavitation bubbles oscillate at the rhythm of
ultrasound waves and collapse, after one or two oscillations,
generating locally very high pressures. In addition, when such
bubble collapses near a solid surface, a phenomenon described
by PLESSET  (illustrated in figure 4d ) occurs. In its collapse
motion, the bubble changes its shape so that a water jet appears
opposite to the substrate and hit the solid surface as a real
hammer (pressure range of about 100 MPa). One can easily
imagine that the jet produces high superficial stresses leading to
local damages (pitting) of the solid material (figure 4 e, f).
Figure 4 : mechanical effects of ultrasounds : a) and b) disbondment
occur by the way of oscillations of stationary cavitation bubbles, c)
ASEM view of a sample after 3 minutes of ultrasonic solicitations.
d) Different steps of the collapse motion of a transitory cavitation
bubble near a solid boundary by M. S. PLESSET . e) ASEM view and f)
optical micrograph picture of surfaces damaged by pitting resulting
from cavitation bubble collapses
The areas of the non stripped zones are quantitatively
measured by means of image analyses based on
recognition software developed in the laboratory. For each curve,
we can notice an horizontal step at the beginning followed by the
decrease of the central non stripped area of paint, but if we
calculate the average radius of this area, we notice that it
decreases rather linearly (figure 5).
The two systems of paint of the figure 5 have opposite
behaviours in natural exposure (left hand pictures on the graphs)
and comparable duration in the flash test. So we must admit that
the strongness/toughness of a system of paint in the flash test
can not be directly related with its durability in natural
On the other hand, as it can be seen also on figure 5 (right hand
pictures on the graphs) , there is two main kind of morphological
aspect of the samples during the test, and it has been possible to
relate this morphology of damages process with the sorting of
the system of paint by their performances in natural exposure.
Then, assuming that the extraction process of large flakes
of paint should lead to a larger dispersion of the stripping kinetic
curves than the pitting process, we expressed a “flash test index”
as the normalized area defined by the dispersion of the graphs
obtained on six samples of the same system of paint (figure 5).
The “flash test index” of eight systems of paint are reported in
Table 1. A classification of efficiency is proposed on this criterion
(greatest index corresponding to lowest efficiency, and smallest
index to highest efficiency) and compared to the long term
behaviour in natural exposure.
A32P : Evo lu tion d e la sur face d e
A32P : Evolution
of non-stripped area
pe intu re fonc tion du tem ps d'exp ositi on
A23P : Evolution de la surface de peintur e
of non-stripped area
ion du temps d' exposit ion aux
str ipped aux
as a function
tag eedde ar e a
su rfa ce res tan t e
p ercent age
s u r n te
non str ipped a rea
as a function of
10 11 12 13 14 15
Figure 5 : graphs for six samples of two systems of paint. The flash test index is
deduced from the area limited by the two extreme (red color) kinetic curves divided by the
time of total stripping.
Table 1 : Efficiency classification : Comparison between flash test and four years
natural exposure results.
four years natural
flakes stripping & pitting
flakes stripping & pitting
The flash test developed for this study, first designed for
the monitoring of the quality stability of industrial materials,
points out some specific parameters which can be interpreted
and correlated to long term efficiency. Especially the morphology
of the stripped particles and consequently the dispersion of
stripping kinetic curves appear to be strongly dependent on the
paint metal adhesion. This property strongly affects the long
term behaviour of the manufactured material. These remarks
induced the definition of a “flash test index” as the ratio of
Measurements carried out on six specimens of the same system
of paint allowed us to establish a paint/metal adhesion
classification of eight systems. The correlation of this last one to
long time natural exposure behaviour revealed a good agreement
between the two types of results. This seems to show that the
flash test could be a short time experiment for paint coating
Department, Région Guadeloupe and Europe for their financial
1. J. PIGERRE , C. Roos, T. Mehinto, I. Pierrejean, P. Rodriguez,
J.L. Mansot, C. Barreau, Prog. Org. Coat. 50 (2004) 132-137.
2. D. QUANTIN
« Les aciers plats revêtus », Colloque « Les
Entretiens de la Technologie »,
CONSEIL (March 15-16,1994).
3. W. FUNKE, J. Coat. Technology, 55 n° 705, (1983) 31-38.
4. H. LEIDHEISER and W. FUNKE, J. Org. Col. Coat. Ass. , 70, n° 5,
5. ISO 9223: Corrosion of metals and alloys-corrosivity of
atmospheres. Classification (1992)
6. J. SCHULTZ, M. F. VALLAT, H. HAIDARA « Films polymères
métallisés : mesure de l’adhésion polymère métal », Eur.
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