Corrosion Behavior of Steel 37 under Dynamic Conditions in 0.1 N
H2SO4
\\Jalan\\

Alaa Abdulhasan Atiyah & Dhuha Albusalih*
1

Department of Materials Engineering, University of Technology, Baghdad, Iraq
Al-Furat Al-Awsat Technical University, Najaf, Iraq

2

*Corresponding author: dhuha.kleef@atu.edu.iq

Abstract
An aggressive environment has a substantial effect on the progression of corrosion on metal surfaces and alloys. This study
investigated the effect of one of the parameters that affect the corrosion process, the stirring rate, on the behavior of Steel
37 in 0.1 N of sulfuric acid. The main method used in this study is an electrochemical method (using a potentiostat at a scan
rate of 3 MV.sec-1), applied at three different temperatures (25, 30, and ˚C). To evaluate the parameters of corrosion in this
study, the Tafel extrapolation method was used. At a constant stirring rate, the corrosion current density was found to be
increased with increasing temperature at a constant stirring rate. In addition, the corrosion rate increased with increasing
stirring rate at a constant temperature due to the rise of the diffusion coefficient of oxygen. The Levich equation was used
to calculate the limiting current densities, as well as the mass transfer coefficient (Km) and the Sherwood number (Sh). The
Km values were calculated and it was found that the mass transfer coefficient was greater at higher temperatures and stirring
rates. The results also revealed that the smallest values of Sh (2.575, 3.897) occurred at 30 °C at two stirring rates (200 and
400 rpm).
Keywords: corrosion failure; dynamic corrosion; limiting current density; Sherwood number; static corrosion; Steel 37.

Introduction
With steel being selected increasingly for numerous applications, failure of steel parts due to corrosion limits
their usage. Particularly in aggressive environments, corrosion failure can be considered a major problem in
many industrial systems. Pipe corrosion and pipe wall thinning due to pressure vessel leakage lead to equipment
failure, which can have catastrophic consequences and lead to considerable economic losses. Several factors
also influence the rate of corrosion development for metals and alloys, i.e., the composition of the alloy [1-8]
and the product operating condition [9-11]. In addition, the environmental hostility degree, which includes the
liquid flow, protective measures, and service life of the product, has also been considered [8]. Flow corrosion
results in rapid premature failure of materials when compared to static corrosion if both are in contact with a
corrosive environment. Work has been carried out to study the effect of flow on mild steel erosion–corrosion
behavior in several corrosive conditions, including acidity, alkalinity, and neutral solutions with corrosive CO2 gas
or erosion particles [12]. Relative motion between the environment and the surface of the metal causes
modification of the metal surface corrosion rate. This phenomenon is chiefly evident in the difficulty of applying
the results of static corrosion testing alone to the selection of fabrics for the construction of chemical process
equipment.
A sequence of simultaneous processes occurs during corrosion, which include physical, chemical, and
electrochemical transport on the metal’s surface during anodic and cathodic polarization. These involve metal
dissolution, passive film formation, the evolution of hydrogen, and the reduction of oxygen. The first of the three
processes requires ionic movement within the liquid phase to and/or from the metal surface under the influence
of the electrical potential gradient. The oxygen reduction reaction requires the diffusion of oxygen molecules
down a chemical potential gradient. The overall electrochemical behavior of the metal is difficult to elucidate
from electrochemical experiments in a stationary solution alone, but it may be ascertained with more confidence
by the introduction of flow [13]. Moreover, it is important to mention that the velocity of the fluid plays an

Copyright ©2023 Published by IRCS - ITB
ISSN: 2337-5779

J. Eng. Technol. Sci. Vol. 55, No. 6, 2023, 639-646
DOI: 10.5614/j.eng.technol.sci.2023.55.6.2

Research Paper

Journal of Engineering and Technological Sciences

640

Alaa Abdulhasan Atiyah & Dhuha Albusalih

essential role in increasing the metal corrosion rate, whereas at higher velocities it may become independent of
this parameter. However, as the speed is further increased, the reduction reaction eventually becomes totally
activation-controlled. Consequently, the reaction rate becomes independent of velocity at very high velocities
[13].
Several studies have been conducted on the mass transfer with the current conditions and corrosion [14-18],
while other studies examined flow-accelerated corrosion (FAC) [19-24]. Both the rotating disc electrode (RDE)
and the rotating cylinder have been effectively implemented in the laboratory to study the flow effect on the
rate of corrosion. They are much faster to use than actual pipelines and other real geometries. Several studies
used RDE in electrochemistry to examine the metal dissolution kinetics under dynamic laboratory conditions
[25-30]. Ethirajulu et al. [33] considered CO2 corrosion prediction in pipe flow under FeCO3 scale-forming
conditions. Donghong Z. et al. [31] examined the impact of hydrodynamics on the boundary layer and the
diffusion boundary layer in the near wall zone on gas–liquid two-phase-flow-prompted corrosion in pipelines.
The study also took into account the hydrodynamic effect of fully developed gas–liquid slug flow in an upward
tube with limiting diffusion current probes. In addition, conductivity probes and digital high-speed video systems
were studied. The study considered both the shear stress and the mass transfer coefficient, particularly in the
near-wall zone. It was found that all increase with the rise of the superficial gas velocity and decrease with the
improvement of the superficial liquid velocity. In addition, the local void fraction of the slug unit and the liquid
slug increases when the superficial gas velocity increases.
Temperature variation plays an important role in metal product corrosion development processes, equipment,
and structures. This can be related to the effects of the rate of all chemical reactions. Few studies have been
implemented to study the effect of temperature on the corrosion rate of steel. Recent research on iron-carbon
alloys in 0.1 N solution suggested that temperature plays an important role in the corrosion progress processes
for the surface of metals and alloys [8]. The authors suggest a considerable effect at different temperatures. The
corrosion rate parameters for the iron–carbon system in 0.1 N solution were calculated at different
temperatures. The study claimed that a temperature increase of 10 °C results in an acceleration of the
dissolution of the iron carbon by approximately 2.3 times. Accordingly, the dissolution of the metal accelerates
as a result. The work also proposed that corrosion increases in iron–carbon alloys with high carbon contents.
The current study addressed the influence of dynamic conditions at 200 and 400 rpm for corrosion of Steel 37
in 0.1 N H2SO4 solution at three temperatures to evaluate the mass transfer coefficients and the Sherwood
numbers.

Experimental Procedure
Material and Chemicals
Steel 37 was used in this work. The used material was cut into a cylindric shape with dimensions of 10 x 10 x 3
mm and it was mounted using a Qx-Machine Inlay hot mounting device (manufactured in China). Mounting was
carried out by formaldehyde (bakelite) at 138 ℃ for 8 minutes. Mounting was conducted by leaving the
specimen’s upper side exposed with a surface area of 1 cm2. In electrochemical studies, suitable provisions were
made on the side for electrical contact. Subsequently, the mounted samples were wet-grounded with silicon
carbide papers of varying degrees (600, 800, 1000, and 1200). During grinding, all samples were rotated 90° for
each degree of grinding paper. The samples were polished using a Ma-Pao 160E Grinder and Polisher machine
(manufactured in China), by using a cloth and alumina slurry with 0.3 µm particle size. The specimens were
polished and washed with water, degreased with methanol, and used for electrochemical tests.
The basic solution was 0.1 N H2SO4 (98%). All experiments were conducted at three different temperatures 25,
30, and 35℃. Stirring speeds were applied at 200 and 400 rpm with a Digital Magnetic Stirrer/Hotplate
Stirrer/Hot plate from Daihan Labtech Co., Ltd.

Corrosion Behavior of Steel 37 under Dynamic Conditions in 0.1 N H2SO4

641

DOI: 10.5614/j.eng.technol.sci.2023.55.6.2

Instruments
The polarization study in this work was carried out in a Winking M Lab 200 Potentiostat from Bank-electronic
using an electrochemical standard cell. Electrochemical measurements were conducted by using a potentiostat
by SCI electrochemical software at a scan rate of 3 mV.sec-1. The studies were started when the open circuit
potential (Eoc) change was less and more than 200 mV average. Two chief measurements were considered:
corrosion potential (Ecorr) and corrosion current density (icorr) additional to the Tafel slope measurement.

Results and Discussions
Figure 1 shows the variation of potential with time for Steel 37 in 0.1 N sulphuric acid under static and dynamic
conditions at 200 and 400 rpm. This figure indicates a small change, i.e., about 20, in the potential under dynamic
conditions.

Figure 1

Potential–time measurements of Steel 37 in 0.1 N H2SO4 solution under dynamic conditions.

Figure 2 shows the Tafel plots of Steel 37 in 0.1 N sulphuric acid at three temperatures under static and dynamic
conditions. Stirring was used to improve the convection in the metal surface neighborhood. Another reason for
using stirring is to lower the thickness of the diffusion boundary layer and to supply the cathodic reactant, i.e.,
oxygen, at a higher rate. The oxygen reduction, therefore, comes to be a more facile process. The corrosion
parameters are listed in Table 1, representing the increase of corrosion current density with increasing
temperature at a constant stirring rate. The table also shows an increase in the current densities with the
improvement of the stirring rate of the medium at a constant temperature. The temperature impacts the
corrosion rate for metals fundamentally by affecting factors that control the oxygen rate diffusion.

642

Alaa Abdulhasan Atiyah & Dhuha Albusalih

Tafel plots of Steel 37 in 0.1 N H2SO4 solution under 0 rpm dynamic conditions.

Tafel plots of Steel 37 in 0.1 N H2SO4 solution under 0 rpm dynamic conditions.

Tafel plots of Steel 37 in 0.1 N H2SO4 solution under 400 rpm dynamic conditions.
Figure 2

Tafel plots of Steel 37 in 0.1 N H2SO4 solution in 0, 200 under 400 rpm dynamic conditions.

Corrosion Behavior of Steel 37 under Dynamic Conditions in 0.1 N H2SO4

643

DOI: 10.5614/j.eng.technol.sci.2023.55.6.2

Table 1 Corrosion parameters of Steel 37 in 0.1 N H2SO4 solution at three temperatures and two stirring
speeds.
Speed
0

200

400

Temp. c°C
25
30
35
25
30
35
25
30
35

Eoc
mV
-514
-523
-524
-512
-526
-509
-523
-506
-510

Ecorr
mV
-544.7
-520.9
-545.6
-524.2
-497.6
-497.9
-495.8
-501.7
-496.5

icorr
μA.cm-2
68.44
71.68
83.27
80.96
112.73
141.38
81.19
119.46
220.25

-bc
mV.dec-1
73.2
205.7
144.6
106.7
151.7
190.2
93.5
120.0
259.9

+ba
mV.dec-1
50.4
130.1
44.7
38.4
80.9
108.2
59.5
83.3
150.7

On the other hand, the velocity mainly affects the rate of corrosion by influencing the diffusion phenomena.
When the velocity affects the limiting diffusion current, this is considered to be a function of the physical
geometry of the system. In addition, the diffusion process is affected by the velocity when the flow conditions
are laminar compared to the turbulence availability. The maximum flux of a species can be derived by the Levich
equation to a unit area of the electrode surface under laminar flow. For a particular species, under isothermal
conditions:

𝑖𝐿 𝛼𝜔0.5

(1)

The theoretical value of the limiting current density (iL) for the oxygen reduction reaction can be evaluated from
the kinematics viscosity (υ), the fluid angular velocity (ω), the diffusion coefficient (D), and the concentration of
oxygen (the electroactive species) (Cb) using the Levich equation [16], as follows:
𝑖𝐿 = 0.62𝐹𝜔0.5 𝐷0.667 𝜐 −0.166 𝐶𝑏

(2)

Eqs. (1) and (2) are usually applied to the analysis of the mass transfer controlled cathodic process and Eq. (2)
predicts a linear dependence of the limiting current density on (ω0.5). Moreover, the extrapolated line should
pass through the origin of the coordinate system, as shown in Figure 3.

Figure 3 Limiting current density of the oxygen reduction versus ω0.5 at different temperatures for Steel 37 in 0.1
N H2SO4 solution under dynamic conditions.

The limiting current density was calculated at three temperatures for the four-electron process mechanism of
the oxygen reduction reaction at various stirring rates. The results are tabulated in Table 2.

644

Alaa Abdulhasan Atiyah & Dhuha Albusalih

Table 2 Limiting current density of Steel 37 in 0.1 N H2SO4 under dynamic conditions.
rpm

ω

ω0.5

200
400

20.93333
41.86667

4.575296
6.470446

25oC
1.178
1.666

iL/ A.cm-2
30 oC
1.185
1.676

35oC
2.003
2.832

The coefficient of mass transfer Km can be calculated approximately using Eq.(3):
K_m=i_L/(zFC_b )

(3)

where z is the transferred charge (= 2), F is the Faraday constant, and Cb is the oxygen concentration. The Km
values are listed in Table 3. They increased as the stirring rate increased. At a constant stirring rate, Km also
increased with increasing temperature.
Table 3 Values of the mass transfer coefficient and Sherwood number.
rpm
200

400

Temp./oC
25
30
35
25
30
35

Km x 10-6
4.73
5.25
9.27
6.69
7.42
13.1

Sh. No. x103
2.815
2.757
4.308
3.982
3.897
6.087

An improvement in iL values is considered to be a result of the increase in stirring and temperature. This results
in an improvement in the oxygen flux that arrives at the surface and decreases in the resistance that restricts
the oxygen transfer.
The mass transfer coefficient (Km) value can often be correlated with the dimensionless quantities Reynolds
number (Re) and Schmidt number (Sc). The mass transfer coefficient is expressed in terms of the Sherwood
number (Sh) as shown in Eq. (4) [32].
Sh = (K_m d)/2D

(4)

where D is the diffusion coefficient, and d is the disc diameter (2.5 cm). The Sherwood numbers are listed in
Table 3. The smallest value of Sh was at 30 °C at a constant stirring rate. This confirms the Tafel plot shifting to
lower values of current densities in Figure 1 at 30 °C.

Conclusions
The results of this study indicate a minor change in the potential variation with dynamic conditions in 0.1 N
sulphuric acid. There was an increase in the corrosion current density with increasing temperature at a constant
stirring rate. There was an increase in the current densities with increasing stirring rate of the medium at a
constant temperature. The results also showed that the temperature changes the metal corrosion rate mainly
by prompting factors that control the oxygen diffusion rate. Finally, as the temperature rises, the diffusion
coefficient of oxygen also increases, which tends to improve the rate of corrosion.

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Manuscript Received: 27 May 2023
Revised Manuscript Received: 26 December 2023
Accepted Manuscript: 28 December 2023