Sustainable Materials and Technologies 11 (2017) 12–18
Contents lists available at ScienceDirect
Sustainable Materials and Technologies
journal homepage: www.elsevier.com/locate/susmat
Green and sustainable local biomaterials for oilfield chemicals: Griffonia
simplicifolia extract as steel corrosion inhibitor in hydrochloric acid
Ekemini Ituen a,b,⁎, Onyewuchi Akaranta b,c, Abosede James c, Shuangqin Sun a
a
b
c
Department of Materials Physics and Chemistry, China University of Petroleum, Qingdao, China
African Centre of Excellence in Oilfield Chemicals Research, Institute of Petroleum Studies, University of Port Harcourt, Nigeria
Department of Pure and Industrial Chemistry, University of Port Harcourt, Nigeria
a r t i c l e
i n f o
Article history:
Received 4 June 2016
Received in revised form 15 December 2016
Accepted 15 December 2016
Available online 18 December 2016
Keywords:
Oilfield chemical
Corrosion inhibitor
EIS
Polarization
Griffonia simplicifolia
a b s t r a c t
Mild steel (MS), X80 and J55 steel are commonly used in construction of oilfield line pipes, casings, tubing and
storage facilities. Their corrosion behaviour was investigated in 1 M HCl solution in absence and presence of
seed extracts of Griffonia simplicifolia (SEGS) at 303 K. Corrosion rates obtained using weight loss technique at
303 K followed the trend J55 N X80 N MS. Inhibition efficiency up to 91.73%, 79.78% and 75.41% for MS, X80
and J55 respectively at 1000 ppm SEGS. SEGS was spontaneously physisorbed on the steel surfaces as best described by Temkin adsorption isotherm. Electrochemical measurements also conducted in the absence and presence of SEGS yielded comparable results. Charge transfer resistance increased as double layer capacitance
decreased due to increase in thickness of SEGS protective film formed. SEGS acted as mixed type inhibitor with
anodic predominance. Scanning Electron Microscopy (SEM) micrographs of the corroded surfaces reveal efficient
protection of all the metal surfaces by addition of SEGS. SEGS could find application as anticorrosive oilfield chemical additive for acidizing, enhanced oil recovery and well treatment fluids.
© 2016 Published by Elsevier B.V.
1. Introduction
The oil and gas industry employs a variety of steel materials for line
pipes, tubing, casings and construction of storage and other facilities.
Depending on application, one of the key factors considered in selecting
the grade of steel is ability to withstand very severe conditions, among
which is corrosive attack [1,2]. These materials deteriorate when they
come in contact with aggressive agents especially acid. Acids like HCl
can be introduced into the pipe work through well stimulation, scale removal or enhanced oil recovery operations [3]. Other acids can be generated in situ through CO2 and H2S dissolution or wastes from some
bacteria. Water itself is a cause of oilfield corrosion because it is a medium where noncorrosive agents like CO2 and H2S dissolve to form corrosive acids [4,5].
Materials selection of corrosion resistant grades of steel is aimed at
reducing corrosion problems. Such steel grades like API 5L X70, X80,
X60, X65, X52 and X42 have now been extensively preferred for line
pipe applications [2,6,7]. Others include API-5CT J55, J55N, N80-P110,
and K55 for welded casing and tubing pipes and mild steel for pipework
and storage facility construction [8,9]. The basic difference in their metallurgy is in the relative amounts of elements blended to fabricate the
⁎ Corresponding author at: Department of Materials Physics and Chemistry, China
University of Petroleum, Qingdao, China.
E-mail address: ebituen@gmail.com (E. Ituen).
http://dx.doi.org/10.1016/j.susmat.2016.12.001
2214-9937/© 2016 Published by Elsevier B.V.
alloys [10]. However, these alloys still corrode or fail and may require replacement or maintenance which could warrant shutting down of plant,
the down production time and other risks which no industry would like
to take [11,12].
Corrosion inhibitors are usually employed to retard the rate of corrosion and increase materials longevity. A wide range of organic adsorption inhibitors currently used in the field are toxic and very expensive.
Paradigm has shifted to ecologically friendly (green) corrosion inhibitors from cheap and sustainable sources. Plant and other biomaterials
sourced locally provide the cheapest and most non-toxic source of corrosion inhibitors [13–15]. Many plants have been tested as corrosion inhibitors for different metals in various corrosive media by several
researchers [16–20], the present study reports SEGS as corrosion inhibitor for different grades of steel used in the oilfield. The wild plant is a
shrub, widely distributed in Southern Nigeria and can propagate rapidly
if cultivated by seeds. It has been classified taxonomically [21] and is
also called children whistle (English), and local names are Arin,
Olabahun, Mba-aba, Alukoko, and Tapara. Application of SEGS as corrosion inhibitor would contribute to local content development, reduce
importation and create internal wealth.
Corrosion inhibitors are believed to act by adsorption [22] resulting
in formation of a thin protective film on the metal surface. Since corrosion is an electrochemical process, the adsorbed layer can be considered
as a double layer formed at the interface between the electrolyte
(corrodent) and metal electrode surface. The self-assembled films
E. Ituen et al. / Sustainable Materials and Technologies 11 (2017) 12–18
13
Table 1
Chemical composition of the steel grades.
Steel Chemical composition (wt.%)
MS
J55
X80
C (0.13), Si (0.18), Mn (0.39), P (0.40), S (0.04), Cu (0.025), Fe (balance)
C (0.24), Si (0.22), Mn (1.1), P (0.103), S (0.004), Cu (0.5), Ni (0.28), Mo
(0.019), Fe (balance)
C (0.065), Si (0.24), Mn (1.58), P (0.011), S (0.003), Cu (0.01), Cr (0.022), Nb
(0.057), V (0.005), Ti (0.024), B (0.0006), Fe (balance)
formed between SEGS and the different grades of oilfield steel were investigated and characterized using electrochemical, gravimetric and
surface examination techniques. Specimens of mild steel (MS), X80
and J55 steels which are frequently used in the oilfield were used for
the study. The nature of interaction of the adsorbed molecules on the respective steels surfaces is predicted using adsorption and thermodynamic models. Hydrochloric acid which is used in acidizing, formation
fracture and enhanced oil recovery was used to simulate the corroding
medium.
2. Material and methods
2.1. Preparation of surfaces of metal specimens
Mild steel (MS) sheets were purchased from Building and Construction Materials Market in Uyo, Akwa Ibom state. The J55 and X80 steel
were purchased from Qingdao Tengxiang Instrument and Equipment
Co. Ltd., China. They were cut into coupons of dimension 2 cm × 2 cm
for gravimetric experiments; 1 cm × 1 cm for electrochemical studies
and 2 cm × 1 cm for surface analysis. The surfaces of the metal coupons
were prepared by following standard procedures reported earlier [23].
In addition, the coupons for electrochemical studies were abraded
using different grades of silicon carbide paper and finished to mirror
surface with CC-22F P1000 grade. The chemical compositions of the
steels were as shown in Table 1 below.
2.2. Preparation of test solutions
The acid was prepared by diluting analytical grade 37% HCl to a concentration of 1.0 M. Mature seeds of Griffonia simplicifolia were harvested from a local bush in Ikot Ambon Ibesikpo, Uyo, Nigeria. The pericarps
were removed and the seeds were air-dried in the laboratory for one
week, ground to powder and soaked in acetone for 48 h. The filtrate
(SEGS) was allowed to air-dry. The dry extract was prepared in the
1 M HCl to concentrations 100 ppm, 500 ppm and 1000 ppm using distilled water.
2.3. Weight loss measurement
The coupons were weighed using Sartorius CPA225D analytical balance of sensitivity ±0.01 mg and immersed in the test solutions with
and without different concentrations of the inhibitor maintained at
303 K for 5 h. Thereafter, they were retrieved, cleaned with detergent
solution with soft brush to remove the corrosion products, washed in
distilled water, dried in air after rinsing in acetone, and reweighed.
The mass losses (mo − m1) were recorded and used to calculate the
Fig. 1. Corrosion rates of MS, J55 and X80 steels in 1 M HCl containing different
concentrations of SEGS at 303 K.
corrosion rate (γ (cmh−1)) of iron of density (ρ (gcm−3)) in the steel
specimens of surface area (A (cm2)) according to Eq. (1). The corrosion
inhibition efficiency (%I) and degree of surface coverage (θ) were calculated using Eqs. (2) and (3) respectively.
γ¼
87:6ðmo −m1 Þ
ρAt
ε WL ¼ 100
ð1Þ
γa −γi
γa
ð2Þ
θ ¼ 0:01 %I
ð3Þ
where mo and m1 are the weights (g) of the coupons before and after
immersion in the test solutions at a time interval, t (sh). The obtained
corrosion rate values were converted to mpy units using conversion factors described in literature [24].
2.4. Electrochemical monitoring techniques
The corrosion process was monitored using Gamry ZRA REF 60018042 electrochemical workstation. The conventional three electrode
set up was used consisting of saturated calomel electrode (SCE) as reference electrode, platinum as counter electrode and the different steel
coupons as working electrode. Electrochemical impedance measurements (EIS) were conducted at frequency of 105 to 10−2 Hz for open circuit immersion time of 30 min at 303 K. The voltage was changed to
−0.15 V to +0.15 V vs. EOC at scan rate of 1 mV/s for Potentiodynamic
Polarization measurements (PDP). Electrochemical Frequency Modulation (EFM) measurements were conducted using two frequencies: 2 Hz
and 5 Hz. The base frequency was 1 Hz, hence the waveform repeats
after 1 s. A peak voltage of 10 mV was used. EChem software package
was used for data fitting and analyses.
Charge transfer resistance from EIS measurements were used to
compute the inhibition efficiency according to Eq. (4). The inhibition
Table 2
Calculated corrosion rate (mpy), inhibition efficiency (%) and degree of surface coverage for corrosion of MS, J55 and X80 in 1 M HCl containing different concentrations of SEGS at 303 K.
System
MS
J55
X80
γ
εWL
Θ
γ
εWL
θ
γ
εWL
θ
0 ppm
100 ppm
500 ppm
1000 ppm
26.72
8.49
3.39
2.21
–
68.23
87.31
91.73
–
0.6823
0.8731
0.9197
54.87
23.35
15.87
13.49
–
57.45
71.08
75.41
–
0.5745
0.7108
0.7541
39.45
13.84
9.47
7.98
–
64.92
76.14
79.78
–
0.6492
0.7614
0.7978
14
E. Ituen et al. / Sustainable Materials and Technologies 11 (2017) 12–18
Fig. 2. Temkin adsorption isotherm for SEGS adsorbed on MS, J55 and X80 at 303 K.
efficiency from PDP and EFM was calculated from the corrosion current
densities using Eq. (5).
εEIS ¼ 100
RctI −RctB
RctI
ð4Þ
obtained for MS in 1000 ppm SEGS and decreased according to the
trend MS N X80 N J55 at all concentrations. This implies that the inhibitor
is more effective with MS than the other grades. Higher efficiency observed for MS may be attributed to larger surface area available for adsorption of inhibitor molecules than J55 and X80 and/or differences in
chemical (Fe) composition of the steel grades.
where RctB and RctI are charge transfer resistances in the absence and
presence of inhibitor respectively.
εPD ¼ 100 1−
Iicorr
3.2. Surface coverage and adsorption isotherm
!
Ibcorr
ð5Þ
where Ibcorr and Iicorr are the corrosion current densities in the absence
and presence of the inhibitor respectively; and RPi and RPb are the polarization resistances with and without the inhibitor respectively. The
magnitude of the double layer capacitance (Cdl) of the adsorbed film
was calculated from constant phase element (CPE) constant (Y0) and
charge transfer resistance (Rct) using Eq. (6)
1n
C dl ¼ Y 0 Rct n−1
ð6Þ
where n is a constant showing degree of roughness of the metal surface
obtained from the phase angle given that (j2 = − 1)α is the phase angle
of CPE and n = 2α/(π) is the CPE exponent.
2.5. Scanning electron microscopic study
By using AMETEX S4800 TSL model operated at 5.0 kV, the micrographs of the metal surfaces were recorded in the vacuum mode after
immersion in 1 M HCl in the absence and presence of 1000 ppm SEGS
for 5 h.
3. Results and discussion
3.1. Weight loss measurement
The corrosion rates of the different steel grades were higher in the
free acid solution than in the inhibited solutions. The highest corrosion
rate was recorded for J55 steel and the corrosion rate decreased according to the trend J55 N X80 N MS (Table 2). However, in the presence of
the inhibitor, corrosion rate decreased greatly as can be seen by downward movement of the curves representing different concentrations of
the inhibitor in Fig. 1. This observation demonstrates effective inhibition
of corrosion of the different steel grades by the SEGS.
The effectiveness of the extracts in reducing the corrosion rate of the
metals is estimated in terms of the inhibition efficiency (εWL). The calculated εWL values are given in Table 1. Inhibition efficiency increased as
concentration of inhibitor increased. The highest εWL of 91.73% was
The fractional surface coverage (θ) of SEGS on the different steel
grades followed the same trend as εWL as shown in Table 2. The coverage
of SEGS on metal active sites and formation of thin protective film that
shields metal surface from the aggressive acid could have led to the reduction in corrosive attack. Fractional surface coverage data were fitted
into different adsorption isotherm models to help explain the nature of
interaction(s) in the adsorbed layer. The models tested were Langmuir,
Temkin, Freundlich, Florry Hugins, Frumkin and El-Awady et al. While
the coverage data of SEGS on all the metal specimens best fitted into
Temkin models (R2 ≥ 0.998). The plots in Fig. 2 depict linear fittings obtained from Temkin adsorption isotherm. The parameters deduced from
the plot are listed in Table 3.
The Temkin isotherms can be expressed as shown in Eq. (7) below.
θ¼−
1
1
ln C−
ln K ads
2a
2a
ð7Þ
where C is the inhibitor concentration, Kads is the adsorption-desorption
equilibrium constant used to describe how strongly the inhibitor molecules are adsorbed on the metal surface, a is the lateral molecular interaction parameter used to predict whether there is attraction or
repulsion in the adsorbed layer [25].
The values of a obtained using Temkin isotherm were all negative indicating that there was repulsion in the adsorbed layer [26]. The
strength of repulsion followed the trend X80 N J55 N MS. The adsorption-desorption equilibrium constant values show considerable binding
strength between the inhibitor and metals, with stronger strength on
X80 surface. This demonstrates that SEGS would provide better protection for pipework, casings and tubings.
Table 3
Parameters deduced from Temkin adsorption isotherm for SEGS.
Steel grade
−a
Kads (ppm−1)
ΔGads (kJmol−1)
R2
MS
J55
X80
4.765
6.316
7.642
6.992
14.560
208.71
−15.016
−16.865
−23.572
0.998
0.993
0.994
E. Ituen et al. / Sustainable Materials and Technologies 11 (2017) 12–18
15
Fig. 3. Nyquist and Bode plots for corrosion of MS, J55 and X80 steels in 1 M HCl in the absence and presence of different concentrations of SEGS.
The free energy of adsorption (Δ Gads) was calculated from Kads
values using Eq. (8).
ΔGads ¼ −RT ln ð55:5K ads Þ
ð8Þ
where 55.5 represents the molar concentration of water. In literature,
when values of ΔGads is around −20 kJmol−1, the adsorption involves
electrostatic interaction (physisorption) while Δ Gads values above
−40 kJmol−1 is attributed to chemisorption [27]. Most of the values obtained in this study are less than −20 kJmol−1 and can be attributed to
physical adsorption mechanism. Results also show possibility of chemical adsorption occurring on X80 steel surface. Such observations can
be also be found in literature [14]. The negative ΔGads values also indicate that the adsorption of SEGS on the metal surfaces is spontaneous.
3.3. Electrochemical impedance spectroscopy
Corrosion of MS, J55 and X80 steel grades were assessed in 1 M HCl
in the absence and presence of different concentrations of SEGS. Nyquist
and Bode diagrams obtained with the different steel grades are shown
in Fig. 3. A single capacitive loop with one capacitive time constant observed demonstrates the occurrence of only one phenomenon. The capacitive loop indicates that charge transfer and double layer
phenomenon occurs at the metal-electrolyte interface. The charge
transfer resistance was obtained by fitting the curves into equivalent
circuit shown in Fig. 4.
The shapes of the Nyquist and Bode diagrams for all the steel grades
and test solutions were similar indicating that the mechanism of corrosion remains the same with or without SEGS. Therefore, addition of inhibitor does not influence the mechanism of corrosion. Diameters of the
Nyquist plot increase as concentration of SEGS in the electrolyte increase corroborating with trend of charge transfer resistance obtained.
This also demonstrates that the influence of the inhibitor on the corrosion rate is concentration dependent. Charge transfer resistance can be
associated with impedance offered by the thin insulating film formed
by SEGS due to adsorption of its molecules on the steel surface. The
thickness and protective efficiency of this film increases with increase
in Rct and inhibitor concentration. A similar behaviour can also be observed with the Bode plots.
The Nyquist plots produced imperfect semicircles, signifying deviations from ideal behaviour. This kind of deviation has been explained
in terms of frequency dispersion of interfacial impedance and attributed
to inhomogeneity of the metal surface arising from surface roughness
[28]. The degree of deviation can be estimated using values of n of the
CPE phase shift, most of which decreased with increase in inhibitor concentration (Table 4). The CPE was introduced instead of a pure capacitor
to compensate for the deviation and the values of n and Y0 of the CPE
were used to compute the double layer capacitance. The values of Cdl decrease on addition of inhibitor (Table 4) which indicate a decrease in the
charge and discharge rates of the capacitor [28]. Decrease in Cdl can also
be due to decrease in local dielectric constant and increase in thickness
of the double layer formed, suggesting strong adsorption of SEGS molecules on the metal surface [27]. A similar trend was observed for all the
grades of steel studied with X80 grade showing the highest difference in
Cdl from that of the blank acid.
The calculated inhibition efficiency increased with increase in SEGS
concentration, similar to the trend of charge transfer resistance. The
highest inhibition efficiency of 96.73% was obtained with X80 grade at
1000 ppm inhibitor concentration. This implies that more SEGS molecules are assembled on X80 making the inhibitor more effective against
Table 4
EIS parameters calculated for MS, J55 and X80 steel grades.
Steel Conc.
(ppm)
Rct
(Ωcm2)
n
Y0
(μΩ−1sn)
Rs
(Ωcm2)
Cdl
(μFcm−2)
εEIS
(%)
MS
102.3
385.5
1089.0
1144.0
76.2
171.3
868.9
1003.2
30.64
124.0
372.1
936.3
0.572
0.566
0.547
0.538
0.555
0.554
0.555
0.625
0.551
0.541
0.554
0.561
157.7
81.62
80.50
60.20
139.6
113.2
115.3
117.8
206.4
126.2
113.8
75.9
1.035
0.999
0.873
0.869
1.131
1.058
0.532
0.983
1.063
1.097
1.038
1.028
127.7
62.2
10.0
3.4
35.1
11.9
3.5
0.8
126.3
10.4
6.5
2.1
–
73.46
90.61
91.06
–
55.52
91.23
92.40
–
75.29
91.77
96.73
J55
X80
Fig. 4. Equivalent circuit model used for fitting EIS data.
0
100
500
1000
0
100
500
1000
0
100
500
1000
16
E. Ituen et al. / Sustainable Materials and Technologies 11 (2017) 12–18
Fig. 5. Molecular structures of some chemical compounds in SEGS.
X80 corrosion than J55 and MS. This can also be attributed to adsorption
of its phyto-compounds like 5-hydroxytryptophan, clomipramine,
griffonin, amitriptyline, fluvoxamine, melatonin, etc. [29] which are
rich in heteroatoms (oxygen and nitrogen) and pie electrons (see structures in Fig. 5). These molecules have large sizes and many potential adsorption sites, hence could adsorb on the steel surface, block the metal
actives sites, achieve large surface coverage and reduce corrosion rate
of the metals. However, at 100 ppm inhibitor concentration, inhibition
efficiency was the lowest (55.52%) with J55 grade.
Table 5
PDP parameters calculated for MS, J55 and X80 steel grades.
Steel Conc.
(ppm)
βa
(mVdec−1)
βc
(mVdec−1)
Icorr
(μAcm−2)
Ecorr
(mV/SCE)
ℇPDP
(%)
MS
95.4
65.9
107.5
124.4
71.3
76.1
60.4
95.8
82.1
103.5
107.3
115.1
64.7
100.3
98.7
92.7
111.2
97.7
78.9
81.2
98.5
124.6
85.0
103.5
969.3
48.8
15.4
14.0
614.9
71.2
62.4
41.5
693.7
114.0
63.0
49.7
−499
−487
−483
−482
−473
−472
−470
−461
−487
−476
−474
−469
–
94.06
98.41
98.55
–
88.42
89.85
93.26
–
83.56
90.93
92.84
J55
3.4. Potentiodynamic polarization
X80
Potentiodynamic polarization measurements were conducted with
the different steel grades to evaluate cathodic and anodic corrosion kinetics in the absence and presence of the inhibitor. The partial electrode
reactions were approximated using Tafel plots (Fig. 6) and the compromise or free corrosion potential (Ecorr) was determined as well as the
corresponding corrosion current density (Icorr). Linear fitting of the
Tafel slopes afforded tafel cathodic and anodic constants, βc and βa respectively. The corrosion potentials obtained for all the metals shifted
to relatively more positive values suggesting that the inhibitor could
be anodic type [30]. However, the differences in Ecorrvalues of the inhibitors from those of the free acid solution were not up to 85 mV, hence
not sufficient to categorize the inhibitor as cathodic or anodic type.
Therefore, EGS can be considered as mixed type inhibitor which inhibits
the corrosion process by geometric blocking of both cathodic and anodic
surface active sites of the different steel grades. Also, corrosion current
density reduced in the presence of the inhibitors and with increase in
SEGS concentration (Table 5) demonstrating the inhibitive effects of
SEGS. The inhibition efficiency also increased with increase in inhibitor
concentration, similar to EIS and weight loss results. Addition of inhibitor was also found to influence the Tafel constants in different ways for
the different metals. While it seems to increase the constants for MS and
X80, the constants showed no definite trend for J55. Inspection of the
Tafel constants reveals the trend MS N J55 N X80 for βa and
X80 N MS N J55 for βc. Also, there are larger dispersion in βa values
0
100
500
1000
0
100
500
1000
0
100
500
1000
than βc which suggests anodic predominance of the inhibitor. This demonstrates that SEGS is a mixed type inhibitor but with predominant anodic activity. The shapes of the curves are similar, supporting that the
inhibitor does not change the mechanism of partial corrosion reactions
at the electrodes [30].
3.5. Electrochemical frequency modulation
EFM measurement was also carried out using small signals to obtain
corrosion current values without prior knowledge of the Tafel slopes.
The corrosion rate, corrosion potential and casuality factors (CF-2 and
CF-3) were also obtained as displayed in Table 6. Inhibition efficiency
calculated from corrosion current values varied with inhibitor concentration similar to results of other measurements, but lower in magnitudes compared to EIS, PDP and LPR results. Experimental causality
factors CF-2 and CF-3 calculated from the frequency spectrum of the
current responses were close to theoretical values with MS and J55
steels indicating that the measurements are of good quality [31].
Fig. 6. Tafel plots for MS, J55 and X80.
E. Ituen et al. / Sustainable Materials and Technologies 11 (2017) 12–18
to Prof. A. P. Udoh, Prof. Hu, Dr. Li, Dr. Wang, Ubong Jerome, Min, Cheng
and Xiang Xiqiang in UPC for their assistance.
Table 6
EFM parameters for MS, X80 and J55 steels.
Steel Conc.
(ppm)
Icorr
(μAcm−2)
βa
(mVdec−1)
βc
CF-2
(mVdec−1)
CF-3
ℇEFM
(%)
MS
162.6
64.9
63.6
41.7
367.4
107.1
87.3
49.4
473.9
276.8
181.0
102.4
64.4
87.5
90.6
92.3
83.7
87.5
85.9
89.5
40.8
93.1
84.6
85.6
107.8
94.4
97.9
100.2
93.4
83.8
97.6
117.4
42.7
105.2
103.3
93.0
2.358
2.362
2.206
2.240
2.727
2.094
2.792
2.211
1.704
3.728
3.000
2.828
–
60.04
60.87
74.33
–
70.85
77.34
86.56
–
41.59
62.60
78.39
X80
J55
0
100
500
1000
0
100
500
1000
0
100
500
1000
17
1.966
1.898
1.487
1.706
2.177
2.655
2.089
2.137
0.945
1.895
1.708
1.350
However, CF-2 exceeded theoretical values with X80 steel, suggesting
the influence of electrochemical noise on that measurement.
3.6. Surface morphology and protection
Fig.7 shows scanned micrographs of the surfaces of different steel
grades after immersion in 1 M HCl in the absence and presence
1000 ppm SEGS. It can be seen from the micrographs that the surface
of the metals, especially J55 steel were greatly damaged (images on
the left) in the absence of the inhibitor. However, in the presence of
SEGS, the pitting or corrosive attack on the metals surfaces reduced. Inspection of the images on the right hand column reveals that SEGS provided good protection for all the metals studied.
Acknowledgements
The authors are pleased to acknowledge the World Bank for support
to carry out laboratory work abroad through the Robert S. McNamara
Fellowship Programme. We also appreciate Materials Physics and
Chemistry Department, China University of Petroleum Qingdao for providing facilities for carrying out this research and African Centre of Excellence in Oilfield Chemicals Research for their support. EI is grateful
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