Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi
In order to on-line detect the ground grid corrosion, the relationship between the corrosion rate of Q235 steel and electrical resistance was studied by an accelerated corrosion in the soil where a 750 kV high-voltage transformer substation was established. The corrosion products and morphology were...
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Фізико-механічний інститут ім. Г.В. Карпенка НАН України
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| Цитувати: | Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi / Yan Aijun, Hou Juanling, Chen Yi, Feng Lajund // Фізико-хімічна механіка матеріалів. — 2011. — Т. 47, № 1. — С. 104-108. — Бібліогр.: 9 назв. — англ. |
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irk-123456789-1381302018-06-19T03:06:52Z Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi Yan Aijun Hou Juanling Chen Yi Feng Lajund In order to on-line detect the ground grid corrosion, the relationship between the corrosion rate of Q235 steel and electrical resistance was studied by an accelerated corrosion in the soil where a 750 kV high-voltage transformer substation was established. The corrosion products and morphology were characterized by SEM (scanning electron microscopy) and XRD (X-ray diffraction). The results show that the rusty layer by the accelerated corrosion has the same structure as that by natural corrosion, and the corrosion products consisted mainly of γ-Fe₂O₃ and Fe₃O₄. One-year monitoring was conducted and the relationship of the corrosion rate (V) and the resistivity (R) was established. The error between the nature corrosion rate and the calculated corrosion rate is less than 3%. В операційному режимі виконано пришвидшені корозійні випробування сітки електричного заземлення зі сталі Q235 у ґрунті трансформаторної підстанції. Залежність глибини корозії від електричного опору сітки вивчали на спеціальній установці. Особливості корозії металу та склад її продуктів досліджували за допомогою сканівної електронної мікроскопії та методу рентгенодифракції. Встановлено, що продукти корозії сталі Q235 відповідають природі іржі, утвореної під час тривалої експлуатації сіткової конструкції. На основі річних спостережень запропоновано формулу для визначення швидкості корозії сталі за цих умов. В операционном режиме проведены ускоренные коррозионные испытания сетки электрического заземления из стали Q235 в почве трансформаторной подстанции. Зависимость глубины коррозии от электрического сопротивления сетки изучали на специальной установке. Особенности коррозии металла и состав ее продуктов исследовали с помощью сканирующей электронной микроскопии и метода рентгенодифракции. Установлено, что продукты коррозии стали Q235 отвечают природе ржавчины, образованной во время длительной эксплуатации сеточной конструкции. На основе годовых наблюдений предложено формула для определения скорости коррозии стали при данных условиях. 2011 Article Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi / Yan Aijun, Hou Juanling, Chen Yi, Feng Lajund // Фізико-хімічна механіка матеріалів. — 2011. — Т. 47, № 1. — С. 104-108. — Бібліогр.: 9 назв. — англ. 0430-6252 http://dspace.nbuv.gov.ua/handle/123456789/138130 en Фізико-хімічна механіка матеріалів Фізико-механічний інститут ім. Г.В. Карпенка НАН України |
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In order to on-line detect the ground grid corrosion, the relationship between the corrosion rate of Q235 steel and electrical resistance was studied by an accelerated corrosion in the soil where a 750 kV high-voltage transformer substation was established. The corrosion products and morphology were characterized by SEM (scanning electron microscopy) and XRD (X-ray diffraction). The results show that the rusty layer by the accelerated corrosion has the same structure as that by natural corrosion, and the corrosion products consisted mainly of γ-Fe₂O₃ and Fe₃O₄. One-year monitoring was conducted and the relationship of the corrosion rate (V) and the resistivity (R) was established. The error between the nature corrosion rate and the calculated corrosion rate is less than 3%. |
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Article |
| author |
Yan Aijun Hou Juanling Chen Yi Feng Lajund |
| spellingShingle |
Yan Aijun Hou Juanling Chen Yi Feng Lajund Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi Фізико-хімічна механіка матеріалів |
| author_facet |
Yan Aijun Hou Juanling Chen Yi Feng Lajund |
| author_sort |
Yan Aijun |
| title |
Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi |
| title_short |
Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi |
| title_full |
Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi |
| title_fullStr |
Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi |
| title_full_unstemmed |
Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi |
| title_sort |
study on soil corrosion principles of the q235 steel ground net in weinan shaanxi |
| publisher |
Фізико-механічний інститут ім. Г.В. Карпенка НАН України |
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2011 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/138130 |
| citation_txt |
Study on soil corrosion principles of the Q235 steel ground net in Weinan Shaanxi / Yan Aijun, Hou Juanling, Chen Yi, Feng Lajund // Фізико-хімічна механіка матеріалів. — 2011. — Т. 47, № 1. — С. 104-108. — Бібліогр.: 9 назв. — англ. |
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Фізико-хімічна механіка матеріалів |
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2025-07-10T05:10:05Z |
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| fulltext |
104
Ô³çèêî-õ³ì³÷íà ìåõàí³êà ìàòåð³àë³â. – 2011. – ¹ 1. – Physicochemical Mechanics of Materials
STUDY ON SOIL CORROSION OF THE Q235 STEEL GROUND GRID
IN WEINAN SHAANXI
YAN AIJUN, HOU JUANLING, CHEN YI, FENG LAJUND
Xi’an University of Technology, P. R. China
In order to on-line detect the ground grid corrosion, the relationship between the corrosion
rate of Q235 steel and electrical resistance was studied by an accelerated corrosion in the
soil where a 750 kV high-voltage transformer substation was established. The corrosion
products and morphology were characterized by SEM (scanning electron microscopy) and
XRD (X-ray diffraction). The results show that the rusty layer by the accelerated corrosion
has the same structure as that by natural corrosion, and the corrosion products consisted
mainly of γ-Fe2O3 and Fe3O4. One-year monitoring was conducted and the relationship of
the corrosion rate (V) and the resistivity (R) was established. The error between the nature
corrosion rate and the calculated corrosion rate is less than 3%.
Keywords: ground grid, accelerated corrosion, soil, electric resistance.
The ground grid is used for the system of earthing, lightening protection and
protective earthing of transformer. At present, the corrosive degree of the ground grid
is evaluated by the change of the electrical resistance of actual ground grid which is
usually regarded as a pure electrical resistance network during detection [1, 2]. Hence,
it is necessary for the ground grid corrosion monitoring to establish a relation between
corrosion rate and electrical resistance.
Due to the low corrosion rate in soil, it takes a quite long time to establish a for-
mula between corrosion rate and electrical resistance [3]. Consequently, no literature
on the new-built high-voltage transformer substation is available. In the present investi-
gation the relation of the corrosion rate and resistance of the ground grid was studied
utilizing the electrolytic accelerated corrosion method [4]. The research can afford
theory basis for on-line ground grid monitoring of the new built high-voltage transfor-
mer substation.
Experimental methods. The Q235 steel with the dimension of 1100×58.9×7.7 mm
was selected as the ground grid material in the study, and soil collected from the depth
of 0.8 m in the construction site of 750 kV transformer station at Weinan City of
Shaanxi Province was adopted as the corrosion medium. The physical and chemical
properties are given in Table 1.
The experiment devices include an adjustable 110 V–15 A voltage-stabilized DC
source, an ammeter with a range of 0–3 A, an electrical resistance of 1 Ω, and a ca-
thode box with the sizes of 1000×120×80 mm.
The cathode box was firstly filled with soil [5], followed by burring a polished
Q235 steel sample in the box. Considering a partial exposure of actual ground grid to
the air, and the error caused by the galvanic corrosion at the joints, the covered length
of soil is 850 mm and other potion was exposed to the air. The experimental principle
is shown in Fig. 1.
Corresponding author: HOU JUANLING, e-mail: houjuanling@yahoo.cn
105
Table 1. Physical and chemical properties of soil in Weinan, Shaanxi Province
Resistivity,
Ω·m
Oxidation & reduction
potential, mV
Water
content, %
Porosity,
%
pH
values
Na+,
mg/kg
K+,
mg/kg
48.98 322 19.46 33.7 7.89 65.45 48.62
Ca2+,
mg/kg
Mg2+,
mg/kg
Cl–,
mg/kg
2
4SO − ,
mg/kg
3NO− ,
mg/kg
3HCO− ,
mg/kg
Total salt,
mg/kg
140.42 38.59 12.75 136.36 95.39 621.2 1160
At the initial stage of the experiment,
the circuit system was corrected, i.e. the
voltage of the standard electrical resistance
was read by a multimeter, then the current
was calculated and corrected until it was
equal to the reading of the ammeter. Then,
one hour after the soil was moistened, the
corrosion test was conducted. The charge
exerted on samples can be solved by inte-
gration on the collected current of the cir-
cuit. The theoretical corrosion rate was
calculated by Faraday’s law (see Eq. (1))
[6], and the practical corrosion rate by
Weight-loss method (see Eq. (2)) [7].
2t
Q M kV
F S t
⋅
= ⋅
⋅ ⋅ ⋅ ρ
, (1)
1 2
m
m m kV
S t
−
= ⋅
⋅ ρ
. (2)
In the equations, Vt and Vm represent the theoretical and practical corrosion rate,
mm/a; Q is the exerted charge, C; M is the mole quantity of iron, g/mol; 2 is the num-
ber of losing electron number when Fe is corroded into Fe2+; F is the Faraday’s cons-
tant, 1 F = 96485 C; S is the surface area of samples covered with soil, m2; t is the
corrosion time, h; k is the conversion factor of the corrosion rate unit from g·m–2·h–1 to
mm/a, 8.76; ρ is the density of iron, g·cm–3; m1 and m2 are the practical mass of samp-
les before and after corrosion, g.
The Transformer Station Comprehensive Diagnosis System of ground grid Faults’
was employed to measure the electrical resistance. Its principle is to apply a constant
direct current at both ends of samples, detect the voltage of the sample at a certain
length, and calculate the electrical resistance. The variation of electrical resistance after
corrosion can be obtained by dividing the electrical resistances before and after corro-
sion.
Experimental results and discussion. Relation between electrolytic current and
time. The change of electrolytic corrosion current with time is shown in Fig. 2. In this
figure the electrolytic current drops rapidly during the initial 5 h, while current has no
obvious change if the time is above 5 h. In order to accelerate corrosion, water was
added into the cathode box every 24 h to restore the maximum current.
The reason why the corrosion electric current decreases with time can be explained
as follows. Three sorts of water, i.e. free water, bound water and equilibrium water,
exist in soil [8]. When the water in soil exists as free water, the salinity in the soil can
move freely, resulting in a higher electric conductivity, as shown in the early stage of
Fig. 1. Schematic diagram of the test:
1 – direct electric current;
2 – cathode box; 3 – steel samples;
4 – soil medium.
106
less than 5 h (Fig. 2). When it is as the
bound water, both the water and salt in the
soil will be absorbed in the internal soil,
and, thus, the moving distance will be
constrained, and the resistivity of the soil
increases, as illustrated in the range of 5 to
24 h. When water of soil is in equilibrium
state, the soil will be almost dry, thus
causing much higher resistivity.
Current efficiency of electrolytic
corrosion. The theoretical and practical
corrosion rate of the samples could be
calculated by equations (1) and (2). The
current efficiency could be obtained from the equation η = (practical corrosion rate/
theoretical corrosion rate) ×100%.
As seen in Table 2, the current efficiency decreases from about 90% at initial cor-
rosion to less than 85% for the later period. That derives from the fact that all
theoretically calculated current is exclusively treated as electrolytic current. In fact,
there is some electrical resistance in the practical medium. In addition, the sample
surface is adhered with a large amount of corrosion products during the corrosion
process, which increases the electrical resistance, and thus decreases the corrosion rate.
On the other hand, partial Fe will be corroded into Fe3+ at strong current, which will
consume one more charge when compared with Fe2+. This is not coincided with the
assumption in the theoretical calculation. Therefore, the practical ground grid materials
have a larger corrosion rate at the initial stage, and lowered corrosion rate once the
corrosion products film was formed.
Table 2. The current efficiency of corrosion process
Theoretical corrosion rate, mm 0.30 1.06 1.95 3.05 4.75 6.27 6.80 8.66
Practical corrosion rate, mm 0.28 0.96 1.67 2.60 4.03 5.29 5.73 7.26
Current efficiency, % 93.33 90.57 85.64 85.25 84.84 84.37 84.26 83.83
Analysis of corrosion products. In order to verify whether the relationship
between the corrosion data and the resistance can be used in the practical diagnosis, the
morphology of the carbon steel samples for electrolytic accelerated corrosion and
natural corrosion was checked by SEM, and the corrosion products were analyzed by
XRD. It is found that surface rusty layer in the electrolytic corrosion is almost the same
as in natural corrosion. Two layers present in the samples. The Fe2O3 product is formed
in the internal layer due to the corrosion of Q235 steel, while the external layer consists
of the mixture of corrosion products and substance in soil as SiO2, Al2SiO5 and CaCO3
[9]. Due to no tight bond with the matrix surface, the external layer is easily peeled off
in the later treatment. The corrosion products were characterized by XRD. The XRD
patterns of accelerated-corroded Q235 steel and nature-corroded Q235 steel are shown
in Fig. 3a and Fig. 3b, respectively.
From Fig. 3, it could be known that Si in Q235 material was transformed into
SiO2 under the two corrosion conditions. In the accelerated corrosion, the corrosion
products of carbon steel are α-Fe2O3, γ-Fe2O3, Fe3O4, FeOOH and FeSiO3 in natural
corrosion. Although there are some differences in the corrosion products under both
corrosion conditions, the main corrosion products are almost the same, which are
mainly γ-Fe2O3 and Fe3O4.
Fig. 2. Electrolytic current – time curve.
107
Fig. 3. XRD energy spectrum of Q235 rusty scale in: a – accelerated corrosion
(■ – SiO2, ▼ – γ-Fe2O3, ◁ – Fe3O4); b – nature corrosion
(■ – SiO2, △ – α-Fe2O3, ▼ – γ-Fe2O3, ◁ – Fe3O4, ► – FeOOH, – FeSiO3).
Relationship between corrosion rate
and resistivity. In Fig. 4, it can be seen that
the electrical resistance increases slightly
with the corrosion rate. When the corrosion
rate is less than 2.02 mm, the change in the
electrical resistance is quite low, which is
no more than 2. When the corrosion rate
reaches 2.94 mm, the variation in electrical
resistance is 4.9 times. At a depth of
3.63 mm, the sample is in severe corrosion
state and the corrosion is almost finished,
while the variation in electrical resistance
is 8.4 times.
Based on the electrical resistance
equation, the direct current electrical re-
sistance is related with the inherent para-
meters, such as the resistivity, the length
and the cross section areas of the metal conductors. As the corrosion progresses, the
decreased cross-section of the samples leads to the increase in electrical resistance. The
following equation can be obtained by fitting the non-linear curve in Fig. 4.
2
1.029
0.21 0.311( 1.029) 0.008( 1.029)
RV
R R
−
=
+ − − −
(mm). (3)
The fitting is shown as the dotted line in Fig. 4, and the related coefficient of
fitting curve R2 is over 0.99.
In-situ test. After one-year monitoring on the ground grid corrosion of 750 kV
transformer substation in Weinan city of Shaanxi Province, the corrosion morphology
of the ground grid buried beneath 0.8 m at the substation was observed. It was found
that the corrosion occurred on the surface but no great change in the electrical resis-
tance was detected after 3 months. After 12 months, the measured resistance is 1.037,
and the corrosion rate calculated by formula (3) is 0.038 mm, while the practical
corrosion rate obtained by the Weight-loss experiment is 0.039 mm. The error is only
2.56%, which can meet the requirement of the in-site test on the ground grid corrosion.
Fig. 4. The variation of electrical resistance
with corrosion rate:
1 – experiment curve; 2 – fitting curve.
108
CONCLUSION
The electrolytic accelerated corrosion of Q235 ground grid was studied by simu-
lating soil environment of Weinan city of Shaanxi Province. Under the constant vol-
tage, the electrolytic corrosion electric current of Q235 steel in soil changes with cor-
rosion time. At the initial stage of 5 h, the electrolytic current drops significantly, and
the current changes slightly above 5 h. The electrolytic efficiency decreased from the
90% to 85% with increase of corrosion rate. The electrical resistance of Q235 steel in
corrosion increases with the corrosion rate. The corrosion products in electrolytic
accelerated corrosion of Q235 steel are similar to the natural corrosion, which are
mainly composed of γ-Fe2O3 and Fe3O4. The relationship between corrosion rate V and
electric resistivity R is established. The error between that in site test and the calculated
value is less than 3%.
РЕЗЮМЕ. В операційному режимі виконано пришвидшені корозійні випробування
сітки електричного заземлення зі сталі Q235 у ґрунті трансформаторної підстанції. Залеж-
ність глибини корозії від електричного опору сітки вивчали на спеціальній установці.
Особливості корозії металу та склад її продуктів досліджували за допомогою сканівної
електронної мікроскопії та методу рентгенодифракції. Встановлено, що продукти корозії
сталі Q235 відповідають природі іржі, утвореної під час тривалої експлуатації сіткової
конструкції. На основі річних спостережень запропоновано формулу для визначення
швидкості корозії сталі за цих умов.
РЕЗЮМЕ. В операционном режиме проведены ускоренные коррозионные испыта-
ния сетки электрического заземления из стали Q235 в почве трансформаторной подстан-
ции. Зависимость глубины коррозии от электрического сопротивления сетки изучали на
специальной установке. Особенности коррозии металла и состав ее продуктов исследова-
ли с помощью сканирующей электронной микроскопии и метода рентгенодифракции.
Установлено, что продукты коррозии стали Q235 отвечают природе ржавчины, образо-
ванной во время длительной эксплуатации сеточной конструкции. На основе годовых на-
блюдений предложено формула для определения скорости коррозии стали при данных
условиях.
1. Experimental study and data process of soil corrosion / Dong Chaofang, Li Xiaogang et al. //
Corros. Scie. and Protec. Technol. – 2003. – 15(3). – P. 157–159.
2. Corrosion Experimental Methods and Anti-Corrosion Test Technology / Wu Yinshun, Fang
Zhi et al. – Beijing: Chemical Industry Press, 1996. – P. 67–69; 142–147.
3. Li Changrong and Qu Zuyu. Correlation among corrosive factors of soil // J. of University of
Science and Technology Beijing. – 1996. – 3. – P. 21–25.
4. GaoYing and Zhang Shuquan. Study on the indoors accelerated corrosion in soil in Lingning
Province // Corros. Scie. and Protec. Technol. – 1992. – 4(3). – P. 204–208.
5. Accelerated corrosion methods of concrete iron electrolyte in concrete / Fang Congqi, Qian
Zhiwei, et al. // Concrete. – 2007. – 2. – P. 16–19.
6. Feng Naixiang. Aluminum Electrolyte. – Beijing: Chemical Industry Press, 2006. – P. 96–97.
7. Zhao Maiqun and Lei Ali. Corrosion and Protection of Metals. – Beijing: National Defense
Industry Press, 2002. – P. 85–86.
8. Chemical Principles / Zhong Qin, Chen Qianqiao, et al. – Beijing: National Defense Industry
Press, 2007. – P. 330.
9. Monitoring the corrosion susceptibility of mild steel in varied soil textures by corrosion
product count technique / E. E. Oguzie, I. B. Agochukwu, et al. // Mater. Chem. and Phys.
– 2004. – 84. – P. 1–6.
Received 17.06.2010
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