Reactivity of polyester aliphatic amine surfactants as corrosion inhibitors for carbon steel in formation water (deep well water)

Corrosion Science 48 (2006) 813–828

www.elsevier.com/locate/corsci

Reactivity of polyester aliphatic aminesurfactants as corrosion inhibitors for

carbon steel in formation water(deep well water)

A.M. Alsabagh a, M.A. Migahed a,*, Hayam S. Awad b

a Department of Petroleum Applications, Egyptian Petroleum Research Institute (EPRI),

Ahmed El-Zomor Street 1, Nasr City, Cairo 11727, Egyptb Chemistry Department, Faculty of Girls for Science, Art and Education, Ain Shams University,

Asmaa Fahmi Street, Helliopolis, Cairo, Egypt

Received 12 January 2004; accepted 15 April 2005Available online 20 July 2005

Abstract

Effect of different concentrations, 40–200 ppm, of various polyester aliphatic amine surfac-tants on inhibition of the corrosion of carbon steel in the formation water (deep well water)was investigated. These surfactants exhibit different levels of inhibition particularly at highconcentration (200 ppm). Inhibition efficiencies in the range 86–96% were determined byweight loss method. Comparable results were obtained from electrochemical measurementsusing Tafel extrapolation and polarisation resistance methods. It was shown that all the inves-tigated surfactants act primarily as anodic inhibitors; however, they also affect the rate andmechanism of the cathodic reaction. These compounds function via adsorption on reactivesites on the corroding surface reducing the corrosion rate of the metal. It was revealed thatthe adsorption of these surfactants obey Langmuir adsorption isotherm. The inhibition effec-tiveness increases with the length of the aliphatic hydrocarbon chain, being a maximum inthe presence of surfactant IV (�96% efficiency). The corrosion inhibition feature of thiscompound is attributed to the presence of a long hydrocarbon chain that ensures large surface

0010-938X/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.doi:10.1016/j.corsci.2005.04.009

* Corresponding author.E-mail address: [email protected] (M.A. Migahed).

mailto:[email protected]

814 A.M. Alsabagh et al. / Corrosion Science 48 (2006) 813–828

coverage as well as the presence of multiple active centers for adsorption. Scanning electronmicroscopy, SEM, has been applied to identify the surface morphology of carbon steel alloyin the absence and presence of the inhibitor molecules.� 2005 Elsevier Ltd. All rights reserved.

Keywords: Corrosion inhibition; Carbon steel; Polyester aliphatic amine surfactants; Formation water

1. Introduction

Carbon steel is a common constructional material for many industrial units be-cause of its low cost and excellent mechanical properties. However, it suffers severeattack in service particularly in oil and gas production systems. Although corrosioninhibitors are the most effective and flexible mean of corrosion control in oil and gasproduction systems, the selection and application of inhibitors are actually compli-cated because of the variable corrosive environments in these systems.

Many organic compounds containing oxygen, nitrogen and sulphur atoms havebeen used as corrosion inhibitors for carbon steel in various aggressive environments[1–6]. The addition of high molecular weight organic compounds such as surfactantsto combat corrosion of carbon steel has found wide application in many fields. It hasbeen reported that these compounds possess high inhibition efficiencies for steel cor-rosion [7–9].

It was reported that the inhibition process by surfactants is attributed primarily tothe adsorption of the surfactant molecules, via their functional group, onto the metalsurface [10]. There are many studies in the literature exploring the relationship be-tween adsorption and corrosion and many useful analytical methodologies havebeen developed in this field [11–16].

In fact, introduction of ethylene oxides into surfactant molecule (ethoxylation) in-creases the inhibitive effect of surfactant [17]. The presence of these groups increasesthe solubility of surfactant and hence the extent of its adsorption on the metal sur-face increases and consequently its inhibitive action improves. Many studies on theinhibition of the corrosion of carbon steel by some ethoxylated surfactants have beencarried out in different corrosive environments [18,19].

Osman et al. [17] investigated the effectiveness of benzyltriethanol ammoniumchloride (BTAC) and its ethoxylate (EBTAC) in inhibiting the corrosion of carbonsteel in 0.1 M H2SO4. It was found that both BTAC and EBTAC act as good cor-rosion inhibitor for carbon steel with the latter being more effective. The authors be-lieve that these compounds adsorb on the steel surface forming a monolayer thatshields the surface from the corrosive environment. Hanna et al. [18] studied theinhibitive action of some ethoxylated fatty acid derivatives. They found that thesecompounds are effective corrosion inhibitors for mild steel corrosion in HCl andH2SO4 and behave as mixed type inhibitors. Other study of the effect of some otherethoxylated fatty acids on the corrosion inhibition of low carbon steel has been car-ried out in the formation water [19]. It was shown that the length of the hydrocarbonchain and number of the double bonds in the molecule have a direct effect on the

A.M. Alsabagh et al. / Corrosion Science 48 (2006) 813–828 815

amount of surfactant adsorbed and hence the inhibition efficiency. Migahed et al.[20] studied the effectiveness of some ethoxylated amine surfactants, N-propyl aminolauryl amid and three of its ethoxylated derivatives, on the corrosion inhibition ofcarbon steel in 1 M HCl. These ethoxylated additives were found to act as good cor-rosion inhibitors and their effectiveness increases with the increase in the number ofthe ethylene oxide units.

Formation water [21] that naturally exists in the rocks before drilling contains avariety of dissolved organic and inorganic compounds. This water considers themost corrosive environments in oil field operations due primarily to the presenceof large quantities of the corrosive carbon dioxide and hydrogen sulfide in additionto other aggressive salts such as chloride and sulfate. The formation water also con-tains traces of oxygen that could enter into the sour brine system. Although non-ionic surfactants are widely used for inhibiting the corrosion of carbon steel in oilfield since they exhibit significant inhibition efficiencies in acid media [22,23], therehave been few studies of inhibition of the corrosion of carbon steel in formationwater. The aim of the present work was, therefore, to investigate the inhibitive actionof some ethoxylated non-ionic surfactants on the corrosion of carbon steel in theformation water.

In this work, weight loss and polarisation curve measurements were carried out todetermine the corrosion rates and mechanism from an electrochemical point of view.In addition, scanning electron microscopy, SEM, has been applied to identify thesurface morphology of the carbon steel alloy in the absence and presence of inhibitormolecules. Surface tension measurements were also carried out to investigate theadsorption behavior of the studied surfactants.

2. Experimental details

2.1. Chemicals

Four water-soluble polyester aliphatic amine surfactants (I–IV) with the generalchemical formula:

[MA_(O_CH2_CH2)X

_N_(CH2_CH2

_O)Y _MA_BP]n

R

were applied in this study, where MA is the maliec anhydride C4H2O3, BP is theblock polymer of polyoxyethylene polyoxypropylene (Mw = 5000), X + Y = 10and R is an aliphatic hydrocarbon chain. R = C10H21 for surfactant I, C12H25 forsurfactant II, C14H29 for surfactant III and C16H33 for surfactant IV. These com-pounds were synthesized as follows [24]:

Ethoxylated amine (0.55 mol) and block polymer (0.55 mol) were stirred with anefficient stirrer and then heated to 80 �C by means of a thermostatic mantle under astream of nitrogen gas. Maliec anhydride (1 mol) was then added and the mixturewas heated to 15 �C for 3 h and then to 19 �C for 4 h and then the temperature

Table 1Characteristics of the formation water

Property pH Sp. gr. (60/60 F) Fe3+ (ppm) Ca2+ (ppm) Mg2+ (ppm) Cl� (ppm)

Value 5.7 1.18 28,500 24,620 3800 120,150


was kept constant at 190–200 �C for 1 h. The progress of the reaction was followedby monitoring the acid number.

The formation water used in this investigation was obtained from Qarun Petro-leum Company, Western Desert, Egypt. The most important characteristics of thiswater are listed in Table 1.

2.2. Materials

The specimens were cut from unused petroleum pipelines as regular edged cuboidswith dimensions 2 · 2 · 0.2 cm. The percentage chemical composition of the carbonsteel alloy used is listed in Table 2.

2.3. Measurements

All the measurements were carried out in air-saturated solutions and at ambienttemperature (21 �C).

2.4. Weight loss measurements

Weight loss measurements were carried out using a Sartorius analytical balancewith precision of 0.1 mg. The working specimens were polished with 600-grit SiCpaper until previous coarse are removed, degreased in acetone, washed with bi-dis-tilled water and finally dried. Triplicate specimens were applied in each experimentand the mean weight losses were reported. The corrosion product is a colloidalprecipitate of Fe(OH)3, thus it was washed several times with bi-distilled waterand then an ultrasonic bath was used to clean the surface of the samples.

2.5. Electrochemical measurements

These measurements were performed using an electrochemical cell similar to thatdescribed by Greene [25] with a platinum electrode used as an auxiliary electrode andsaturated calomel electrode as a reference electrode. Electrochemical measurementswere carried out using Wenking model 4B81M potentiostat.

Table 2Chemical composition of carbon steel alloy

Element C S P Ni Mn Si Cr Mo Fe

Composition (wt%) 0.18 0.007 0.008 0.04 1.8 0.007 0.04 0.04 Rest


2.6. Surface tension measurements

Water-soluble polyester aliphatic amine surfactants (I–IV) were subjected to sur-face tension measurements at different concentrations (1 · 10�8–8.4 · 10�3 M). Sur-face tension determination was carried out using Drop Volume Tensiometer‘‘Lauda-Konigshofen/Deutchlandocal’’ at 298 K.

2.7. Scanning electron microscopy (SEM) examination

The surface examination was carried out using scanning electron microscope (Jeol5400); the energy of the acceleration beam employed was 30 kV.

3. Results and discussion

3.1. Corrosion weight loss tests

These were carried out in the formation water in the presence of different concen-trations (0–200 ppm) of the surfactants (I–IV). A general trend is observed in thepresence of all the investigated surfactants, a decrease in the weight loss of carbonsteel in the presence of these additives even at a low concentration (40 ppm) com-pared to the blank, surfactant free, solution. The effect of these compounds appearsto be significant after a long time of immersion. Increasing the surfactant concentra-tion results in a further decrease in the weight loss of carbon steel to be the lowest at200 ppm concentration. Furthermore, the effect of these surfactants increases withincreasing the length of the hydrocarbon chain (R).

These preliminary results have indicated that all the studied surfactants could actas corrosion inhibitors for carbon steel in the formation water particularly at highconcentrations, but to different extent. Among these is surfactant IV that showedthe best performance as seen that from Fig. 1 which presents the weight loss of car-bon steel in the formation water in the absence and presence of different concentra-tions of surfactant IV as a function of time. This compound significantly reduces theweight loss of carbon steel particularly at a high concentration (200 ppm).

Corrosion rate, calculated from weight loss, is presented as a function of inhibitorconcentration for all the different surfactants in Fig. 2. This clearly shows the effectof concentration where the corrosion rate decreases as the inhibitor concentrationincreases to be a minimum at 200 ppm. It is also evident from this figure that inhib-itor IV exhibits the best inhibition effect since it shows the lowest corrosion rate at allthe investigated concentrations compared with the others.

The inhibition efficiency g (%) is determined from weight loss using therelationship

g ¼ ðRwðfreeÞ � RwðinhÞÞ=RwðfreeÞ � 100; ð1Þ

where Rw(free) and Rw(inh) are the weight loss in the absence and presence of inhibitor,respectively. Table 3 reports the percentage efficiency and corrosion rate in the

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50

Time (Day)

Wei

ght

loss

(m

g cm

-2)

Blank 40 ppm 80 ppm

120 ppm 160 ppm 200 ppm

Fig. 1. Weight loss as a function of time for carbon steel in the formation water with differentconcentrations of inhibitor IV.

0

0.5

1

1.5

2

2.5

0 50 100 150 200 250

Concentration (ppm)

Cor

rosi

on R

ate

(mg

cm-2

day

-1)

Inhibitor I Inhibitor II Inhibitor III Inhibitor IV

Fig. 2. Corrosion rate of carbon steel after 30 days immersion in the formation water in the presence of200 ppm of inhibitors (I–IV).


presence of 200 ppm of the inhibitors (I–IV). The studied surfactants can bearranged according to their inhibition effect as follows: IV > III > II > I.

It is generally agreed that the primary action in the inhibition process by surfac-tants is the adsorption of the surfactant molecules via their functional group onto themetal surface [10]. Therefore, it was of a particular interest to investigate the phe-nomenon of adsorption of such compounds and determine the degree of surface cov-erage (h) by the adsorbed surfactant molecules. The degree of surface coverage iscalculated from weight loss (hwtloss) using the relationship

Table 3Corrosion rate, degree of surface coverage and percentage efficiency (obtained from weigh loss) after 30days in the formation water in the absence and presence of 200 ppm of inhibitors (I–IV)

Inhibitor Corrosion rate(mg cm�2 day�1)

Degree of surfacecoverage (h)

Percentageefficiency g (%)

Formation water 1.92 – –I 0.258 0.866 86.6II 0.208 0.892 89.2III 0.126 0.934 93.4IV 0.082 0.958 95.8


hwtloss ¼ 1� RwðinhÞ=RwðfreeÞ. ð2Þ

The values of hwtloss determined in the presence of 200 ppm of the different inhibitorsare reported with the corrosion rates and percentage efficiencies calculated at thesame concentration in Table 3. hwtloss are in good agreement with the corrosion rateresults. As indicated from Table 3, the higher the degree of the surface coverage thelower the corrosion rate of carbon steel and hence the higher the inhibitor efficiency.

It is clearly evident from Table 3 that inhibitor IV exhibits the highest extent ofsurface coverage, corresponding to the best inhibition effect. hwtloss in the presenceof this surfactant approaches unity, indicating almost a full coverage of the surfacewith the adsorbed surfactant molecules. These appear to act as a good physical bar-rier shielding the corroding surface from the corrosive environment and thus bring-ing down the corrosion rate of carbon steel very significantly.

To investigate the type of adsorption, Ci/h is plotted against Ci for the surfactants(I–IV) in Fig. 3. The experimental results give straight lines with unit slopes suggest-ing that the inhibitor molecules adsorbed on the carbon steel/formation water inter-face obey the Langmuir adsorption isotherm, which represented by the followingequation:

Fig. 3. Ci/h as a function of logCi for inhibitors (I–IV).


Ci=h ¼ 1=kads þ Ci; ð3Þwhere Ci is the inhibitor concentration and kads represents the adsorption equilib-rium constant. It is clear from Fig. 3 that the adsorption ability follows the order:IV > III > II > I, indicating that the adsorption ability of the investigated surfactantsincreases with increasing the chain length of the alkyl group in the surfactantmolecule.

3.2. Potentiostatic polarisation measurements

The effect of the different surfactants on the free corrosion potential of carbonsteel was investigated. Fig. 4 shows the measured open circuit potential in the forma-tion water in the absence and presence of 200 ppm of inhibitors I–IV as a function oftime. All the surfactants raise the free corrosion potential of carbon steel (shifted it tomore noble values) compared to the blank solution with the effect of inhibitor IVbeing more pronounced. This initially indicates that the studied aliphatic amine sur-factants act as anodic inhibitors.

The effect of these compounds on the mechanism of inhibition can be investigatedfrom the polarisation curve measurements. Fig. 5 shows an example of the anodicand cathodic polarisation curves measured in the formation water with different con-centrations of inhibitor IV since it showed the best performance. At low concentra-tion, 40 ppm, there is a shift in the corrosion potential to the positive (noble)direction with a significant decrease in the anodic current density. Increasing theinhibitor concentration gives rise to a further shift in the corrosion potential tothe noble direction and a decrease in the anodic current density.

-900

-850

-800

-750

-700

-650

-600

-550

-500

0 50 100 150 200 250

Time (min)

Ope

n C

ircu

it P

oten

tial

(m

V v

s. S

CE

)

Blank Inhibitor I Inhibitor IIInhibitor III Inhibitor IV

Fig. 4. Open circuit potential–time plot for carbon steel in the formation water with 200 ppm of inhibitors(I–IV).

-1100

-1000

-900

-800

-700

-600

-500

-400

1 10 100 1000 10000

Current Density (A cm-2)

Pot

enti

al (

mV

vs.

SC

E)

0 ppm 40 ppm 80 ppm

120 ppm 160 ppm 200 ppm

Fig. 5. Polarisation curves for carbon steel in the formation water in absence and presence of differentconcentrations of inhibitor IV.


It is clearly seen from the polarisation curves that whilst the inhibitor primarilyreduces the anodic, metal dissolution, reaction it appears to affect the rate and mech-anism of the cathodic reaction. Generally, surfactant molecules can inhibit eitheranodic or cathodic reaction either by occupying reactive sites on the corroding sur-face or by simply providing resistance to the supply of oxidant to, or transport ofreaction products away from, the metal surface.

The electrochemical parameters, Ecorr, icorr, ba and bc, determined from the polar-isation curves are presented for inhibitor IV in Table 4. The Table also reports thepercentage efficiency ðgicorr

Þ and degree of surface coverage ðhicorrÞ determined fromthe corrosion current density, icorr, using the relationship

gicorr¼ ði0 � iÞ=i0 � 100; ð4Þ

hicorr ¼ 1� i=i0; ð5Þ

Table 4Electrochemical parameters obtained from polarisation of carbon steel in the formation water in thepresence of different concentrations of inhibitor IV

Concentration(ppm)

Ecorr (mV) icorr

(lA cm�2)ba bc hðicorrÞ gðicorrÞ

(%)

0 �780 90.00 64 64 – –40 �776 29.50 105 136 0.6722 67.2280 �766 23.80 107 129 0.7333 73.34120 �756 22.80 111 120 0.7467 74.67160 �746 19.50 113 123 0.7833 78.33200 �726 12.00 118 100 0.8667 86.67


where i0 and i are the corrosion current densities in the absence and presence ofinhibitor, respectively. As reflected from this table, the corrosion current density de-creases and the corrosion potential increases (being more anodic) as the inhibitorconcentration increases. Furthermore, the degree of surface coverage and the per-centage efficiency increase with increasing the inhibitor concentration.

The degree of surface coverage ðhRpÞ was also determined from polarisation resis-tances (Rp) derived from the corrosion current density using the relationship

Rp ¼ b=icorr; ð6Þwhere b (Stern–Geary constant) = babc/2.303(ba + bc). Table 5 compares the degreesof surface coverage obtained from different measurements, (hwtloss), ðhicorrÞ, ðhRpÞ inthe presence of different concentrations of inhibitor IV. These show similar trend,an increase with the increase in the inhibitor concentration and are in goodagreement.

Tables 6 and 7 compare the inhibition efficiencies derived from different measure-ments for all the studied surfactants. A general trend is observed, an increase in theinhibition efficiencies with increasing the inhibitor concentration. The efficienciesdetermined from weight loss (gwtloss) are in accordance with those derived from cor-rosion current densities ðgicorr

Þ. The inhibition efficiency follows the order:IV > III > II > I.

Table 5Surface coverage determined from different measurements as a function of inhibitor concentration forcarbon steel in the formation water with inhibitor IV

Concentration (ppm) h(wtloss) hðicorrÞ hðRpÞ0 – – –40 0.8081 0.6722 0.823080 0.8613 0.7333 0.8557120 0.8880 0.7467 0.8597160 0.9240 0.7833 0.8850200 0.9575 0.8667 0.9211

Table 6Percentage efficiencies determined from weight loss as a function of inhibitor concentration for carbonsteel in the formation water with inhibitors (I–IV)

Concentration (ppm) Inhibition efficiency

I II III IV

0 – – – –40 39.515 51.334 70.503 80.81580 56.257 64.783 78.665 86.135120 64.679 71.300 82.773 88.804160 76.153 80.797 88.371 92.409200 86.586 89.185 93.449 95.754

Table 7Percentage efficiencies determined from polarisation as a function of inhibitor concentration for carbonsteel in the formation water with inhibitors (I–IV)

Concentration(ppm)

Inhibition efficiency

I II III IV

0 – – – –40 27.37 32.78 46.02 67.2280 34.74 39.87 54.30 73.34120 45.26 49.67 59.68 74.67160 57.90 62.10 67.73 78.33200 62.41 71.78 75.05 86.67


4. Surface tension measurements

Surface tension was measured in the presence of different concentrations of thesurfactants (I–IV). Fig. 6 shows the relationship between the surface tension (c)and ln surfactant concentration, lnC. The intercept of the two straight lines desig-nates the critical micelle concentration (CMC). It is clear that for all types of surfac-tants, the surface tension decreases with increasing the concentration until CMC isreached above which the surface tension is not affect by a further increase in the sur-factant concentration.

On the basis of the view that corrosion inhibition by surfactants depends on theability of these compounds to adsorb on the corroding surface which is directly re-lated to its capacity to aggregate to form clusters (micelles). The critical micelle con-centration (CMC) considers a key factor in determining the effectiveness of

25

30

35

40

45

50

55

60

-20 -15 -10 -5 0

ln C (mol/l)

Surf

ace

Ten

sion

(m

N m

-1)

I II III IV

Fig. 6. Surface tension–lnC isotherm for aliphatic polyester amine surfactants.


surfactants as corrosion inhibitors. Below the CMC, as the surfactant concentrationincreases, the surfactant molecules tend to aggregate on exposed interfaces and thisinterfacial aggregation reduces surface tension and this is what is shown in Fig. 6.The aggregation takes place with the surfactant hydrophobic group directed towardsthe interior of the micelle and its hydrophilic group directed towards the solvent.Micellization is therefore a related mechanism alternative to adsorption at the inter-face for removing hydrophobic groups from contact with the solvents, therebyreducing the free energy of the system [26]. Since this interfacial aggregation occurson a corroding metal surface, it tends to inhibit corrosion. This indicates that reduc-ing the surface tension with increasing the surfactant concentration, below CMC, iscorrelated with the decrease of the corrosion rate of carbon steel. This is clearlyshown in Fig. 7, which illustrates the effect of the surfactant concentration on thecorrosion rate.

On the other hand, increasing the surfactant concentration above CMC does notaffect the surface tension, as shown in Fig. 6, which is, in turn, does not influence thecorrosion rate of carbon steel. This could be attributed to the fact that above CMCthe surface of carbon steel is covered with a monolayer of surfactant molecules andthe additional molecules combine to form micelles or multiple layers of adsorbedsurfactant molecules. This, consequently, does not alter the surface tension and cor-rosion rate.

It has to be noted that for a surfactant to be an excellent corrosion inhibitor itshould exhibit a low CMC value, the inhibition effectiveness decreases as theCMC value increases. On the basis of this view, among all the studied compoundsis surfactant IV which shows the lowest CMC value and hence it considers the mosteffective corrosion inhibitor for carbon steel in this study. This, in fact, agrees withthe weight loss and polarisation results. Surfactant IV appears to create a good

0

0.2

0.4

0.6

0.8

1

1.2

0 0.000002 0.000004 0.000006 0.000008 0.00001

Concentration (M)

Cor

rosi

on R

ate

(mg

cm-2

day

-1 )

I II III IV

Fig. 7. Effect of inhibitor concentration on the corrosion rate of carbon steel in the formation water.


hydrophobic physical barrier to the aggressive ions and this accounts for its highinhibition efficiency.

The surface excess concentration (Cmax) can be calculated from Gibbs equation

Cmax ¼ 1=RT ½dc=d ln C�. ð7ÞCmax values are used to calculate the surface area per molecule (Amin) as follows:

Amin ¼ 1=Cmax � NA; ð8Þwhere NA is the Avogadro�s number.

The data presented in Table 8 show some of the surface active properties for theinvestigated surfactants. It is observed that the surface value of Amin increases withincreasing the chain length of the aliphatic polyester amine surfactant. This is be-cause Amin depends primarily on the adsorption interface which is, in turn, affectedby the total number of carbon atoms in the chain and hence on the hydrophobicityof the surfactant [27].

The results so far have demonstrated that all the investigated surfactants exhibitsome level of inhibition for carbon steel in the formation water but to different ex-tent. It is agreed that the primary action in the inhibition process by surfactants isthe adsorption of these compounds onto the metal surface [10] via at least one func-tional group considered as the reaction center for the adsorption process. Generally,adsorption of inhibitors is attributed to the presence of neucleophilic atoms (such asnitrogen, oxygen, phosphorus and sulphur) and triple bond or aromatic ring in theirmolecular structure. All the surfactants applied in this study contain several sites(such as nitrogen atom as well as many oxygen atoms), which can act as reaction cen-ters for the adsorption of these compounds onto the carbon steel surface. All the sur-factants contain the same number of these centers, but they differ only on the lengthof the aliphatic hydrocarbon chain, i.e. in the total number of carbon atoms in thechain. Thus, the length of the hydrocarbon chain considers the controlling factor inthe inhibition process by these different surfactants.

The results have shown that the effectiveness of the studied compounds as corro-sion inhibitors for carbon steel in the formation water depends primarily on the totalnumber of carbon atoms in the aliphatic hydrocarbon chain, the greater this numberthe more effective is the surfactant. Inhibitor IV that contains the greatest numberof carbon atoms exhibits the best inhibition for the carbon steel corrosion in the

Table 8Some of the surface active properties for the investigated aliphatic polyester amines at 298 K

Inhibitor Parameters

CMC(mol/l)

ccmc

(mN m�1)Cmax · 10�10

(mol/cm2)Amin · 10�3

(nm2)

I 2.5 · 10�4 36 4.6945 0.087II 1.3 · 10�4 34 4.4976 0.091III 9.2 · 10�5 32 3.9936 0.103IV 3.2 · 10�5 30 3.4118 0.120


formation water. This could be attributed to the presence of a long hydrocarbonchain that provides large surface coverage with the strongly adsorbed surfactantmolecules forming a good barrier between the metal surface and the corrosivemedium.

5. SEM examination

Surface examination using scanning electron microscope was carried out to inves-tigate the effect of inhibitor on the surface morphology of carbon steel. Fig. 8(a)shows the micrographs taken to the surface of carbon steel after 6 days immersionin the formation water with no additives. This reveals a badly corroded surface withthe corrosion products are dissipated all over the surface of the specimen in a non-

Fig. 8. Micrographs of the surface of carbon steel after 6 days immersion in: (a) Formation water.(b) Formation water in the presence of 200 ppm of inhibitor IV.


uniform manner. Fig. 8(b) presents the micrographs of the carbon steel surface afterimmersion, for the same period of time, in the formation water in the presence of200 ppm of inhibitor IV which shows a well inhibited surface.

6. Conclusions

1. All the studied surfactants reduce the corrosion rate of carbon steel particularly ata high concentration (200 ppm). The inhibition effectiveness of these compoundsincreases with the total number of carbon atoms in the aliphatic hydrocarbonchain. Surfactant IV shows the best performance over all the studied surfactants,it exhibits an efficiency of �96% at 200 ppm concentration.

2. Inhibition is primarily due to a decrease in the anodic, metal dissolution, reaction.3. The inhibition is attributed to the adsorption of the surfactant molecules onto

reactive sites on the metal surface preventing supply of the aggressive ions tothe surface and/or transport of reaction products away from the surface. Theadsorption of all the studied surfactants obeys Langmuir adsorption isotherm.

References

[1] W.W. Frenier, F.B. Growcock, V.R. Lopp, Corrosion Science 44 (9) (1998) 590.[2] B. Gaur, T.B. Singh, D.D.N. Singh, Corrosion Science 52 (2) (1996) 154.[3] S. Sharma, R. Arora, R.S. Chaudary, Journal of Electrochemical Society, India 48 (3) (1999)

476.[4] M. Ajmal, A.S. Mideen, M.A. Quraishi, Corrosion Science 36 (1) (1993) 79.[5] I. Singh, Corrosion Science 49 (6) (1993) 473.[6] M.A. Migahed, A.A. El-Shafei, M.A. Morsi, Egyptian Journal of Chemistry 45 (3) (2002) 587.[7] A.A. Abdel Fattach, K.M. Atia, F.S. Ahmed, M.I. Roushdy, Corrosion Prevention and Control 33

(3) (1986) 67.[8] M. Elachouri, M.S. Hajji, M. Salem, S. Kertit, E.M. Essassi, Corrosion Science 37 (1995) 381.[9] M. Elachouri, M.S. Hajji, M. Salem, S. Kertit, J. Aride, R. Coudert, E. Essassi, Corrosion 52 (1996)

103.[10] I.L. Rozenfeld, Corrosion Inhibitors, McGraw-Hill, New York, 1981.[11] B.A. Abd-EI-Nabey, E. Khamis, M.Sh. Ramadan, A. EI-Gindy, Corrosion 52 (1996) 671.[12] H. Luo, Y.C. Guan, K.N. Han, Corrosion 54 (1998) 726.[13] M.L. Free, Corrosion Science 44 (2002) 2865.[14] M.L. Free, Corrosion 58 (2002) 1025.[15] S. Omanovic, S.G. Roscoe, Corrosion 56 (2000) 684.[16] T. Zhao, G. Mu, Corrosion Science 41 (1999) 1937.[17] M.M. Osman, A.M.A. Omar, A.M. Sabagh, Materials Chemistry and Physics 50 (1997) 271.[18] F. Hanna, G.M. Sherbini, Y. Brakat, British Corrosion Journal 24 (1989) 269.[19] M.M. Osman, M.N. Shalaby, Materials Chemistry and Physics 77 (2002) 261.[20] M.A. Migahed, H.M. Mahmoud, A.M. Al-Sabagh, Materials Chemistry and Physics 80 (2003)

169.[21] F.N. Speller, Corrosion Causes and Prevention, McGraw-Hill, New York, 1951.[22] M.M. Osman, M.N. Shalaby, Anti-Corrosion Methods and Materials 44 (5) (1997) 318.[23] D. Gobi, N. Bhuvaneswaran, S. Rajeswarai, K. Ramadas, Anti-Corrosion Methods and Materials 47

(6) (2000) 332.[24] W. Hrezuch, K. Kozle, Tenside Surfactants Detergents 38 (2) (2001) 72.


[25] N.D. Greene (Ed.), Experimental Electrode Kinetics, Rensselaer Polytechnic Institute, New York,1962.

[26] W. Adamson, Physical Chemistry of Surfaces, Interscience, New York, 1960.[27] W. Wang, M.L. Free, Anti-Corrosion Methods and Materials 50 (3) (2003) 186.

Documents

Reactivity of polyester aliphatic amine surfactants as corrosion inhibitors for carbon steel in formation water (deep well water)