M. LI et al.: STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A GALVANIZED X80 PIPELINE STEEL ...
645–653
STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A
GALVANIZED X80 PIPELINE STEEL WELDED JOINT DURING A
CYCLIC SALT SPRAY TEST
[TUDIJ POSPE[ENE KOROZIJE ZVARNIH SPOJEV
GALVANIZIRANEGA JEKLA ZA CEVI X80 V POGOJIH
PREIZKU[ANJA Z IZMENI^NIM NAPR[EVANJEM S SLANICO
Mengmeng Li
1
, Hongchao Ji
1,2*
, Chun Han
3
, Shengqiang Liu
2
, Wenchao Xiao
4
1
College of Mechanical Engineering, North China University of Science and Technology, Tangshan 063210 China
2
School of Materials Science and Engineering, Zhejiang University, Hangzhou 310030, China
3
China 22 MCC Group Corporation Limited, Hebei, Tangshan 063035
4
Shenzhen Institute for Advanced Study, University of Electronic Science and Technology of China, Guangdong, Shenzhen 518000, China
Prejem rokopisa – received: 2023-10-24; sprejem za objavo – accepted for publication: 2023-10-20
doi:10.17222/mit.2023.946
The corrosion behavior of galvanized X80 pipeline steel welded joints in a marine atmospheric environment was studied using
the cyclic salt spray accelerated corrosion test. The corrosion weight loss, corrosion morphology and corrosion products of sam-
ples under different cycles were characterized by means of appearance inspection, SEM and EDS. The results show that with the
rupture of the galvanized layer, cracks first appear when the weld metal is exposed for eight days. With the infiltration of the
corrosive liquid, pitting pits first appear in the weld metal. In the early stage of corrosion in the heat-affected zone, the fracture
degree of the zinc layer is more serious than that in the other two areas. The corrosion products of the zinc layer accumulate ir-
regularly and more pits appear, resulting in early cracks and pitting pits in the later stage. Compared with the first two regions,
the base metal shows better corrosion resistance.
Keywords: galvanized alloy steel, X80 pipeline steel, corrosion of welded joints, cyclic salt spray test
V ~lanku je opisan potek pospe{ene korozije zvarnih spojev legiranega jekla za cevi vrste X80 s pomo~jo korozijskega preizkusa
izmeni~nega napr{evanja s slanico, ki simulira atmosferske pogoje na morju oziroma izpostavljenost koroziji plovil med plovbo
po morju. Avtorji so izvedli meritve izgub na masi, analizo morfologije korozijskih produktov, vizualne teste in karaktrizacijo
na vzorcih s pomo~jo vrsti~ne elektronske mikroskopije in mikrokemijskih analiz (SEM/EDS). Rezultati ka`ejo, da se po
poru{itvi galvanizirane plasti razpoke pojavijo po 8 dneh izvajanja preizkusov izmeni~nega napr{evanja. Z infiltracijo
korozivne kapljevine se korozijske jamice pojavijo najprej na zvarih. V zgodnjem stadiju korozije je plast cinka nad toplotno
vplivano cono mnogo bolj po{kodovana kot v ostalih dveh podro~jih (osnovni kovini in kovini za varjenje oziroma podro~je
staljenega dela zvara). Korozijski produkti plasti cinka se nabirajo neenakomerno, pojavljajo se korozijske jamice, kar vodi do
zgodnje tvorbe ve~ razpok in korozijskih jamic v kasnej{ih stadijih korozije. Medsebojna primerjava prvih dvh podro~ij ka`e, da
ima osnovna kovina bolj{o odpornost proti koroziji.
Klju~ne besede: galvanizirano legirano jeklo, jeklo za cevovode vrste X80, korozija zvarnih spojev, cikli~ni test napr{evanja s
slanico
1 INTRODUCTION
In order to carry out efficient transportation of oil and
natural gas, we have higher expectations regarding the
performance of pipeline steel. It should exhibit not only
high strength and toughness, but also greater thickness
and diameter. As a high-strength low-alloy steel, X80
pipeline steel is widely used in oil and gas transport-
ation
1–3
because it can withstand the large pressure gen-
erated inside a pipeline. Welding is an important process-
ing technology in pipeline production and laying. The
main welding processes currently used are submerged
arc welding and gas shielded welding. In the process of
pipeline transportation, the corrosion of pipeline steel
needs special attention
4,5
and the corrosion of pipeline
steel welded joints is one of the key issues.
6
Welded
joints mainly consist of the heat-affected zone (HAZ),
weld metal (WM) and base metal (BM). The heteroge-
neous microstructure and residual stress between these
regions vary significantly, resulting in different corrosion
behaviors of welded joints.
7
Many methods have been
used to prevent the corrosion of low carbon steel, includ-
ing painting, anodizing and chemical conversion coat-
ings.
8
Zinc and zinc-aluminum materials are often used as
sacrificial anode coatings to protect alloy steel substrates
due to their high chemical activity and low price. The
service life of zinc-coated steel can be as long as several
decades because a zinc coating greatly improves the cor-
rosion resistance of steel products exposed to corrosive
environments.
9
A zinc coating protects the underlying
carbon steel substrate by forming a passivation layer, si-
multaneously providing a sacrificial anode. The zinc
coating has a more negative corrosion potential than the
Materiali in tehnologije / Materials and technology 57 (2023) 6, 645–653 645
UDK 620.193:691.714 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 57(6)645(2023)
*Corresponding author's e-mail:
jihongchao@ncst.edu.cn (Hongchao Ji)

steel substrate. During a corrosion process, the zinc coat-
ing preferentially corrodes and acts as an anode, which
contributes to the corrosion inhibition of the steel sub-
strate. The corrosion of galvanized steel occurs in three
steps. First, corrosion occurs due to the dissolution of the
zinc coating, and then corrosion products are formed,
thereby reducing the overall corrosion rate of the zinc
coating. In the second stage, after the local consumption
of the zinc coating, the steel substrate is corroded. In the
final stage, the zinc coating is completely consumed, and
the bare steel substrate is corroded down to the carbon
steel, covered with corrosion products.
10
With the increasing demand for oil and gas energy
around the world, the exploration, exploitation and trans-
portation of oil and gas from unconventional fields (such
as basins, oceans, etc.) have attracted more and more at-
tention. However, there are few studies on the corrosion
of galvanized X80 pipeline steel welded joints in a ma-
rine atmospheric environment. Previous studies focused
on the corrosion of X80 pipeline steel welded joints in
conventional oil and gas environments
11,12
or the corro-
sion of X80 pipeline steel in unconventional oil and gas
environments.
13,14
Igor et al.
7
found that pitting corrosion in the heat-af-
fected zone is more serious than that in the weld or base
metal. Persson et al.
9
found that corrosion products con-
taining sulfates and chlorides (Zn(OH)
2
)
3
·ZnSO
4
·nH
2
O,
NaZn
4
(SO
4
)(OH)
6
Cl·6H
2
O and Zn
5
(OH)
8
Cl
2
·H
2
O were
formed at the anode of a corrosion pit, and
Zn
5
(OH)
6
(CO
3
)
2
was mainly formed on the outside of the
corrosion product and the cathode area of the corrosion
pit. Corrosion of galvanized steel usually begins with lo-
calized corrosion.
15
Wang et al.
16
found that when there
is a zinc layer on a weld interface, the total electrochemi-
cal corrosion performance of the welded joint is im-
proved. The presence of the zinc layer can reduce the
corrosion rate and improve the strength of the weld.
In addition, the corrosion products of zinc coatings
usually have complex structures and a lower conductiv-
ity, which can greatly reduce the electron transport dur-
ing the electrochemical corrosion reaction and/or physi-
cally prevent the migration of corrosion ions to the
underlying substrate. Therefore, the chemical and physi-
cal properties of a zinc coating and its corrosion products
have always made galvanized steel one of the most com-
monly used structural materials.
In this study, based on an accelerated corrosion test
of simulating the effect of a marine atmospheric environ-
ment, the corrosion behavior of galvanized X80 pipeline
steel and its welded joints was characterized using a cy-
clic salt spray accelerated corrosion test, corrosion
weight loss analysis and scanning electron microscopy.
The corrosion behavior of galvanized X80 pipeline steel
and its welded joints was characterized by corrosion ki-
netics, morphology and composition of corrosion prod-
ucts. The study provides a theoretical basis for pipeline
protection measures, improving the corrosion resistance
of weak areas of welded joints, ensuring a safe transpor-
tation and improving the transportation efficiency.
2 EXPERIMENTAL PART
2.1 Material and specimen preparation
The test sample is X80 pipeline steel with a galva-
nized layer on the surface, and Table 1 shows the chemi-
cal composition of X80 pipeline steel.
In the process of sample preparation, the X80 pipe-
line steel plate was first cut into (50 × 18.4 × 10) mm
samples. The surfaces of the samples were successively
polished with 120–2000# water-grinding sandpaper until
there were no defects such as scratches on them. Surface
oil and impurities of the samples were cleaned with an-
hydrous ethanol and the samples were dried in a dry hot
airflow. The samples were then weighed using an elec-
tronic scale (accurate to 0.01 mg). Secondly, the surface
of the X80 pipeline steel was electroplated and the galva-
nized pipeline steel was weighed; the weighing was also
accurate to 0.01 mg. Finally, in accordance with 'GB/T
10125-2012: Corrosion tests in artificial atmospheres –
Salt spray tests', a test was carried out in a programmable
salt spray test chamber.
2.2 Accelerated corrosion test
In this experiment, the acid salt spray dry-wet cycle
accelerated corrosion method was used. The test condi-
tions were as follows: (a) The salt spray composition was
(5 ± 0.5)%NaCl; b) Salt spray process: the nozzle pres-
sure was 80 kPa, the spray temperature was (3 ± 0.5) °C;
(c) Drying process: the temperature was (60 ± 1) °C, RH
< 30 %; (d) Cycle period: an alternating experiment was
carried out including 8 h of spraying + 16 h of drying per
cycle (1 d), and (4, 8, 16, 24, 32 and 40) cycles were
completed. Sampling and corrosion performance testing
were carried out at the test nodes after (4, 8, 16, 24, 32
and 40) d, respectively, in order to grasp the corrosion
behavior and corrosion damage of the material.
2.3 Corrosion performance test
During the test, three test samples with corrosion
products were regularly taken out; two of them were
used for a corrosion weight loss analysis, and one was
processed into several small test pieces by wire cutting
for a morphology and composition analysis.
M. LI et al.: STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A GALVANIZED X80 PIPELINE STEEL ...
646 Materiali in tehnologije / Materials and technology 57 (2023) 6, 645–653
Table 1: Chemical composition of X80 pipeline steel
Chemical composition C Si Mn P S Cr Ni V Ti Mo Nb
w/% 0.0062 0.28 1.85 0.011 0.0006 0.03 0.016 0.059 0.016 0.22 0.1

2.3.1 Corrosion weight loss analysis
After removing the corrosion products, the mass loss
ratio ( m
) and the corrosion rate (v) were calculated us-
ing the mass loss method, expressed by the following
formulas:
 m
=
− mm
m
01
1
(1)
vm m
St
=− 87600
01
()
 (2)
where  m
is the ratio of the mass loss (%); m
0
is the
mass of the uncorroded specimen (g); m
1
is the mass of
the corroded sample after the rust removal (g); v is the
corrosion rate (μm/d);  is the density of the material
(g/cm
3
); s is the surface exposed to the corrosive envi-
ronment (cm
2
); t is the corrosion time (h). In addition,
the cross-sectional area of the parallel sample is the av-
erage of four equidistant cross-sectional areas in the
corrosion area of the sample. The ratio of the cross-sec-
tional area loss  A is defined as:
ΔA
AV A
A
=
−
1
0
(3)
where A
0
is the cross-sectional area (cm
2
) of the parallel
sample before corrosion, and A
1
is the cross-sectional
area (cm
2
) of the parallel sample after corrosion.
2.3.2 Corrosion morphology observation
The macroscopic morphology of a corrosion sample
was observed using a digital camera, and the appearance
inspection and macroscopic photography were per-
formed. The surface morphology of the samples after
corrosion was observed with a metallographic micro-
scope and scanning electron microscope (SEM), while
the chemical composition of the corrosion products was
analyzed with EDS and X-ray diffractometer (XRD).
The determination was carried out with a SCIOS focused
ion beam field emission scanning electron microscope
produced in Czechia. The voltage was 20 kV and the
current was 0.8 nA. The model of the X-ray diffracto-
meter was APD2000PRO. The scanning range 2 was
10–100°, the step width was 0.0 ° and the scanning rate
was 10°/min.
3 RESULTS AND DISCUSSION
3.1 Corrosion kinetics
The data for the corrosion weight loss and corrosion
rate of the samples exposed to an accelerated corrosion
environment for different times are shown in Table 2,
and the curve of the corrosion exposure time is shown in
Figure 1. It can be seen from the corrosion weight loss
and corrosion rate curves of the X80 pipeline steel ex-
posed to an accelerated corrosion environment for differ-
ent times that the accelerated corrosion exposure of X80
pipeline steel can be roughly divided into four stages. In
the first stage (4–16 d), the trend of corrosion weight loss
and corrosion rate increased slowly, indicating that the
zinc layer had a good protective effect on the substrate at
the initial stage of corrosion. In the second stage
(16–24 d), the trend of corrosion weight loss and corro-
sion rate increased more slowly and the difference be-
tween the two groups was lower than that in the first
stage. At this time, the zinc layer was locally corroded,
M. LI et al.: STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A GALVANIZED X80 PIPELINE STEEL ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 645–653 647
Table 2: Corrosion data for galvanized X80 pipeline steel welded joints exposed to an accelerated corrosion environment for different times
Exposure time 0 d 4 d 8 d 16 d 24 d 32 d 40 d
Sample 1
Weight loss (g/cm
2
) 0 0.005 0.020 0.057 0.110 0.205 0.318
Corrosion rate (um/d) 0 1.75 3.15 4.54 5.83 8.17 10.10
Sample 2
Weight loss (g/cm
2
) 0 0.005 0.016 0.047 0.095 0.163 0.236
Corrosion rate (um/d) 0 1.75 2.62 3.76 5.01 6.47 7.51
Figure 1: Corrosion weight loss curve and corrosion rate curve of galvanized X80 pipeline steel welded joints

and the corrosion products produced due to the exposed
substrate were combined with the corrosion products of
the galvanized layer, increasing the protection of the sub-
strate. In the third stage (24–40 d), with the extension of
the exposure time, the zinc layer on the surface of the
substrate was completely corroded, and the surface rust
layer began to loosen or even fall off. The unprotected
substrate surface was affected by corrosive media such
as Cl and H+, resulting in a rapid increase in the corro-
sion weight loss and corrosion rate.
3.2 Corrosion morphology analysis
Figure 2 shows the macroscopic morphology of gal-
vanized X80 pipeline steel exposed to an accelerated cor-
rosion environment for different periods. By observing
M. LI et al.: STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A GALVANIZED X80 PIPELINE STEEL ...
648 Materiali in tehnologije / Materials and technology 57 (2023) 6, 645–653
Figure 2: Macroscopic diagram and the measuring point of a galvanized X80 pipeline steel welded joint
Figure 3: Microstructure of a galvanized X80 pipeline steel welded joint in an accelerated corrosion environment for 4 d: a) weld metal, b)
heat-affected zone, c) base metal

and comparing, it can be seen that when exposed for 4 d,
the surface of the sample was evenly covered with
gray-white corrosion products dominated by the galva-
nized layer, while other areas retained the original color
and luster. When exposed for 8 d, the corrosion products
of the coating expanded over the whole surface, which
lost its luster, and the corrosion products of the local zinc
layer began to fall off. The exposed substrate surface be-
gan to corrode and form a brown rust layer, mixed with
the corrosion products of the white galvanized layer.
When exposed for 16 d, most of the surface of the sam-
ple was covered by the brown rust layer. In addition to
the loose and easy-to-shed rust layer on the surface, the
brown-red rust layer still covered most of the surface, but
the local area was still mixed with the white-coating cor-
rosion products. When exposed for 24–40 d, the corro-
sion products of the coating completely peeled off, and
the brown rust layer was regenerated, completely cover-
ing the entire surface. As the corrosion time increased,
the thickness of the surface rust layer gradually increased
and the color gradually deepened. The sampling areas
for SEM and EDS are shown in Figure 3.
Figure 3 shows the microstructure of a welded joint
of galvanized X80 pipeline steel kept in an accelerated
corrosion environment for 4 d. It can be seen that the
broken zinc layer in the base metal region was relatively
flat compared with the HAZ and BM regions, and the
whole region had a regular strip shape. The fractured
zinc layer plane in the weld area began to accumulate to
a certain extent, but the whole area still had a regular lath
shape. The broken zinc layer in the heat-affected zone
began to accumulate obviously, and the corrosion prod-
ucts were mostly broken zinc layers, showing irregular
polygons. At the same time, due to the irregularity of the
corrosion products, there were many pits on the surface
of the heat-affected zone.
Figure 4 shows the microstructure of a galvanized
X80 pipeline steel welded joint kept in an accelerated
corrosion environment for 8 d. It can be seen that the
corrosion products on the surface of the entire welded
joint were denser than those after 4 d, but they were still
dominated by bright galvanized layer corrosion products.
The accumulation of corrosion products also began to
occur in the base metal area, but the corrosion products
on the surface of the base metal still mainly belonged to
the zinc layer. The strip-like corrosion products in the
weld area were gradually connected to form a dense 'pro-
tective layer', but it began to crack in some parts. The
zinc layer on the surface of the heat-affected zone repre-
sented a dense 'protective layer'. At this time, the zinc
layer ruptured more seriously, and the corrosion products
were mostly fine needles.
Figure 5 shows the microstructure of a galvanized
X80 pipeline steel welded joint kept in an accelerated
corrosion environment for 16 d. At this time, the corro-
sion products of the local galvanized layer began to fall
off, and the exposed part of the substrate began to cor-
rode and produce a rust layer, having a mixed and inclu-
sion morphology with the corrosion products of the
white coating. The boundary between the zinc layer and
the substrate in the weld zone was most obvious because
the surface mixed rust layer was loose and cracked, fall-
ing off under the action of corrosive media such as Cl-.
Fine cracks with low brightness began to appear in the
matrix. The remaining coating on the surface of the
heat-affected zone was evenly distributed across the ex-
posed substrate, but serious cracks appeared. In addition
to the local inclusion of white coating corrosion products
M. LI et al.: STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A GALVANIZED X80 PIPELINE STEEL ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 645–653 649
Figure 4: Microstructure of a galvanized X80 pipeline steel welded joint in an accelerated corrosion environment for 8 d: a) weld metal, b)
heat-affected zone, c) base metal

in the base metal area, most of the surface was mixed
and replaced by the rust layer formed by the corrosion of
the substrate, while fine cracks began to appear at the
junction.
Figure 6 shows the microstructure of a galvanized
X80 pipeline steel welded joint kept in an accelerated
corrosion environment for 24 d. When exposed for this
period, the corrosion products of the galvanized layer
were basically peeled off; the rust layer on the surface of
the substrate was regenerated and it expanded across the
surface of the whole welded joint. At this time, the gran-
ular corrosion products in the base metal area began to
appear and were scattered across the surface. The granu-
lar corrosion products in the weld area began to accumu-
late; at the same time, small cracks began to appear in
the rust layer on the surface of the substrate and large
cracks appeared in the whole weld area. The granular
corrosion products in the heat-affected area were seri-
ously accumulated, and honeycomb dense granular prod-
ucts gradually covered the cracks on the surface.
Figure 7 shows the microstructure of a galvanized
X80 pipeline steel welded joint kept in an accelerated
M. LI et al.: STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A GALVANIZED X80 PIPELINE STEEL ...
650 Materiali in tehnologije / Materials and technology 57 (2023) 6, 645–653
Figure 5: Microstructure of a galvanized X80 pipeline steel welded joint in an accelerated corrosion environment for 16 d: a) weld metal, b)
heat-affected zone, c) base metal
Figure 6: Microstructure of a galvanized X80 pipeline steel welded joint in an accelerated corrosion environment for 24 d: a) weld metal, b)
heat-affected zone, c) base metal

corrosion environment for 32 d. It can be seen that the
accumulation rate of corrosion products in the heat-af-
fected zone was much smaller than the process of rust
layer rupture and spalling in this area. Cracks were still
there, showing a more serious trend. When exposed for
32 d, the rust layer in the weld area gradually became
dense due to the corrosion liquid, penetrating deep into
the cracks. Some areas began to show pitting pits, ac-
companied by small cracks. The corrosion degree of the
base metal area was lower than that of the other two ar-
eas. Although the accumulation of the surface corrosion
products was more serious, only small cracks appeared.
Figure 8 shows the microstructure of a welded joint
of galvanized X80 pipeline steel kept in an accelerated
corrosion environment for 40 d. At this stage, the pitting
corrosion pits at the weld gradually expanded, and the
entire weld area was covered with dense pitting corro-
sion pits. In the heat-affected zone, pitting pits began to
appear when cracks still existed and occupied nearly half
of the area. The corrosion products in the base metal area
began to show regular floccules, and no obvious cracks
or pitting pits appeared.
M. LI et al.: STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A GALVANIZED X80 PIPELINE STEEL ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 645–653 651
Figure 7: Microstructure of a galvanized X80 pipeline steel welded joint in an accelerated corrosion environment for 32 d: a) weld metal, b) heat
affected zone, c) base metal
Figure 8: Microstructure of a galvanized X80 pipeline steel welded joint in an accelerated corrosion environment for 40 d: a) weld metal, b) heat
affected zone, c) base metal

3.3 Analysis of the corrosion product change
EDS results for corrosion products in different re-
gions of the welded joints of galvanized X80 pipeline
steel after exposure to different cycles are shown in Ta-
bles 3, 4 and 5. From the EDS results and XRD dia-
grams, it can be seen that the corrosion products gener-
ated during the corrosion process gradually transitioned
from the galvanized layer to the substrate rust layer. The
corrosion products on the surface of the samples exposed
for 4–8 d were mainly ZnO. When exposed for 16 d, the
corrosion products of the coating fell off locally, and an
Fe oxide rust layer of the matrix gradually appeared.
When exposed for 24–40 d, the corrosion products of the
galvanized layer were basically peeled off and replaced
by the rust layer, and the content of Fe gradually in-
creased with the increase in the thickness of the rust
layer. In addition, the corrosion products contained cer-
tain amounts of Cl, Na and other elements, mainly due to
the deposition of the salt solution sprayed during the test.
Table 3: Elements of corrosion products in the weld zone of a galva-
nized X80 pipeline steel welded joint in w/%
Exposure
time/d
OF eZ nC lN a
4 24.32 3.43 68.93 1.64 1.70
8 37.83 3.51 47.13 11.53 –
16 42.08 12.35 45.12 0.36 1.10
24 22.56 61.61 13.93 1.90 –
32 0.93 95.73 1.48 1.86 –
40 0.31 99.30 0.37 0.02 –
Table 4: Elements of corrosion products in the heat-affected zone of a
galvanized X80 pipeline steel welded joint in w/%
Exposure
time/d
OF eZ nC lN a
4 20.96 4.37 62.20 11.52 0.95
8 19.09 3.04 64.13 13.66 0.09
16 15.04 14.04 63.95 6.95 0.02
24 33.69 54.29 7.97 4.04 –
32 3.59 94.82 0.42 1.17 –
40 – 99.60 0.40 – –
Table 5: Elements of corrosion products in the base metal area of a
galvanized X80 pipeline steel welded joint in w/%
Exposure
time/d
OF eZ nC lN a
4 22.54 5.70 58.20 12.72 0.83
8 28.24 5.55 39.73 6.78 0.79
16 28.66 11.04 48.09 12.21 –
24 7.12 73.53 17.73 1.62 –
32 23.09 72.35 0.40 4.15 –
40 4.5 94.06 0.33 1.11 –
4 CONCLUSIONS
1) The corrosion rate of a galvanized X80 pipeline
steel welded joint increases slowly at first and then in-
creases extremely. In the early stage of corrosion, due to
the protection of the zinc coating on the substrate, the
trend of the corrosion weight loss and corrosion rate in-
crease slowly. In the middle stage of corrosion, the cor-
rosion products produced on the exposed substrate are
combined with the corrosion products of the galvanized
layer, providing better protection. In the later stage of
corrosion, the galvanized layer on the surface of the sub-
strate peels off completely and its protection is lost. The
surface of the substrate is affected by corrosive media
such as Cl and H +, resulting in a rapid increase in the
corrosion weight loss and corrosion rate.
2) The corrosion change made to the galvanized X80
pipeline steel welded joint includes the following pro-
cesses: the formation of galvanized layer corrosion prod-
ucts; local spalling – galvanized layer corrosion products
basically spall; matrix rust layer formation – galvanized,
matrix, corrosion-product, mixed-matrix, rust-layer
growth; and gradual thickening over the entire sample
surface.
3) After8dofe xposure, the zinc layer in the weld
metal begins to crack, and it begins to lose its protection
of the matrix, thus reducing the corrosion resistance. The
corrosive liquid is in direct contact with the matrix after
the crack is penetrated, which accelerates the reaction
rate, resulting in the first occurrence of pitting pits in the
weld metal after 32 d of exposure. When exposed for
16 d, cracks appear in the base metal and heat-affected
zone at the same time. However, compared with the nar-
row and obvious cracks in the heat-affected zone, the
cracks in the base metal are almost invisible. Therefore,
after the same exposure time, the base metal shows better
corrosion resistance. In the early stage of corrosion, the
corrosion degree of the zinc layer in the heat-affected
zone is more serious than that in the other two regions.
And due to an irregular accumulation of corrosion prod-
ucts, there are many pits on the surface. This leads to an
accumulation of the corrosive medium in the middle
stage of corrosion, so cracks and pitting pits in the
heat-affected zone also appear early.
M. LI et al.: STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A GALVANIZED X80 PIPELINE STEEL ...
652 Materiali in tehnologije / Materials and technology 57 (2023) 6, 645–653
Figure 9: XRD results for corrosion products of galvanized X80 pipe-
line steel welded joints exposed for different times

Acknowledgment
This work was supported by the S&P Program of
Hebei (Grant No. 22281802Z), and also by the Tangshan
Talent Foundation Innovation Team (20130204D), as
well as the Science and Technology Project of the Hebei
Education Department (QN2021117).
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M. LI et al.: STUDY ON THE ACCELERATED CORROSION BEHAVIOR OF A GALVANIZED X80 PIPELINE STEEL ...
Materiali in tehnologije / Materials and technology 57 (2023) 6, 645–653 653