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Paper No. PP1 NIGIS * CORCON 2017 * 17-20 September * Mumbai, India Copyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS. CORROSION INHIBITION OF MILD STEEL USED IN OIL AND NATURAL GAS INDUSTRIES USING 5-PHENYL TETRAZOLE Pratap P.Kamble Chemistry Research Laboratory Department of Chemistry, R.J.College,Ghatkopar,Mumbai,India Email- [email protected] Dr. R.S.Dubey Chemistry Research Laboratory Department of Chemistry, R.J.College,Ghatkopar,Mumbai,India ABSTRACT: The inhibitive action of 5 phenyl tetrazole on corrosion of mild steel in 1 M HCl was studied by weight loss, open circuit potential (OCP) and potentiodynamic polarization technique. The inhibition efficiency increased with increase in concentration of inhibitor. Electrochemical studies support the conclusion that compound is efficient inhibitor for mild steel corrosion. The adsorption of compound obeys Langmuir’s adsorption isotherm. Polarization study indicated that the inhibitor acted as mixed type. The protective film formed on surface is confirmed by scanning electron microscopy (SEM) and energy dispersive analysis by X-ray (EDX).Result obtained from weight loss technique are in good agreement with electrochemical and surface analytical results. Key words: mild steel, corrosion, HCl, Tetrazole, SEM, EDX.

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Page 1: PaperNo. PP1 - icspl.orgicspl.org/Corcon 2017/html/PDF/PP1.pdf · PaperNo. PP1 NIGIS*CORCON2017*17-20September*Mumbai,India Copyright2017byNIGIS.Thematerialpresentedandtheviewsexpressedinthispaperaresolelythoseoftheauthor(s

Paper No.PP1

NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

CORROSION INHIBITION OF MILD STEEL USED IN OIL AND NATURALGAS INDUSTRIES USING 5-PHENYL TETRAZOLE

Pratap P.Kamble

Chemistry Research LaboratoryDepartment of Chemistry, R.J.College,Ghatkopar,Mumbai,India

Email- [email protected]

Dr. R.S.Dubey

Chemistry Research LaboratoryDepartment of Chemistry, R.J.College,Ghatkopar,Mumbai,India

ABSTRACT:The inhibitive action of 5 phenyl tetrazole on corrosion of mild steel in 1 M HCl was studied byweight loss, open circuit potential (OCP) and potentiodynamic polarization technique. The inhibitionefficiency increased with increase in concentration of inhibitor. Electrochemical studies support theconclusion that compound is efficient inhibitor for mild steel corrosion. The adsorption of compoundobeys Langmuir’s adsorption isotherm. Polarization study indicated that the inhibitor acted as mixedtype. The protective film formed on surface is confirmed by scanning electron microscopy (SEM)and energy dispersive analysis by X-ray (EDX).Result obtained from weight loss technique are ingood agreement with electrochemical and surface analytical results.

Key words: mild steel, corrosion, HCl, Tetrazole, SEM, EDX.

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NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

1. INTRODUCTION:Mild steel is the most widely used metal in industrial application due to its excellent mechanicalproperties and low cost [1-3]. Acidic conditions were applied in many industrial methods andprocessing, such as industrial metal cleaning and treating, chemical descaling, and the oil and gasindustry[4-6].An organic corrosion inhibitors is a chemical substance that can be applied to liquid orgas within industrial process to decrease a corrosion rate of metal or its alloy [7]. Organiccompounds containing atoms with a lone pair of electrons (N, O, S and p) can decrease corrosionprocess of metal in aqueous acidic solutions [8].

The aim of this work is to evaluate the corrosion inhibition efficiency of 5-phenyl tetrazole for mildsteel in 1molar HCI using weight loss, open circuit potential, potentiodynamic polarization andsurface analytical techniques such as SEM and EDX.

2. EXPERIMENTAL PROCEDURE:

2.1. MATERIAL AND METHODS:Mild steel refers to low carbon steel which is usually used for structural application in industry. Mildsteel coupons having composition (c-o.16%, si-0.10%, Mn-0.40%, P-0.013%, Si-0.02% andremaining iron.) have been used in present investigation.

SURFACE TRETMENT OF MILD STEEL:

For electrochemical and polarization and gravimetric analysis, coupons of 1cm x 3cm x 0.025cmwere sheared from the commercial grade sheet. The surface of mild steel coupons were abradedsuccessively by different grades of metallographic emery paper 1/0, 2/0, 3/0 and 4/0. So as to getthe surface free from scratches and other apparent defects. Polished sample were wash with soapsolution, rinsed with doubled distilled water, degreased with acetone and finally dried. The surfacetreatment was carried out immediately before each experiment of corrosion test.

TEST SOLUTION:

1M HCI was prepared by dilution of 36% HCI (analytical grade) in bi-distilled water. Theconcentration ranged from 100 to 500 ppm solution of 5- phenyl tetrazole in 1M HCI.

2.2 SYNTHESIS OF INHIBITORS:

The tetrazole used in the present study were synthesized according to previously describedprocedure [9]. The characterization data, IUPAC name, structure and abbreviation used for thesynthesized compound are given below in Table 1.

Inhibitor Molecular Structure Analytical data5-aminotetrazole

MP – 2140C - 2160C.FT-IR- max/cm3.3120,2970,2830,2760,2606,2575,2488,1560,1465,1160,720,703.

Table 1: IUPAC name, molecular structure, melting point and analytical data of studiedinhibitor.

Page 3: PaperNo. PP1 - icspl.orgicspl.org/Corcon 2017/html/PDF/PP1.pdf · PaperNo. PP1 NIGIS*CORCON2017*17-20September*Mumbai,India Copyright2017byNIGIS.Thematerialpresentedandtheviewsexpressedinthispaperaresolelythoseoftheauthor(s

NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

2.3 WEIGHT LOSS MESUREMENTS

Weight loss measurement was carried out in a test tube containing 10 ml test solution with andwithout inhibitors solution at the range from 100 to 500ppm.The immersion time was 24 hours at260C +10C. The coupons were withdrawn from test solution ,rinsed with doubled distilled water,washed with acetone ,dried and weighted .the average value of weight loss were reported.

2.4 OPEN CIRCUIT POTENTIAL (OCP) AND POLARISATION MEASUREMENT

Electrochemical measurement system, DC105, containing software of DC corrosion technique fromM/S Gamery instrument, USA was used for OCP and potential polarization experimental studies.Above mentioned polished and cleaned mild steel coupons were masked with enamel lacquer byleaving 1 cm2 working area on one side and a small portion at the tip to provide electrical contact.Finally the coupons were dried in desiccators for further use. A Saturated calomel electrodes andgraphite electrodes were used as reference and counter electrode respectively. The working surfacearea of mild steel electrodes and remaining these electrodes were sufficiently immersed in to thePyrex glass vessel containing 50ml of test solution and connected to gamery instruments. Potentialwas swept between -0.5 and 0.5v at the scan rate of 5mv/s. the open circuit potential was carriedout for 1 hours to obtained steady horizontal curve and then potentiodynamic polarization wasrun .The variation in potential and polarization of mild steel with respect to with and without inhibitorwas measured against saturated calomel electrode.

2.5 SEM AND EDX ANALYSIS

The composition and surface morphology of corrosion product on mild steel sample after immersionfor 24 hours in 1M HCI in absence and a presence of 500 ppm of 5-phenyl tetrazole, was studiedusing a SEM and EDX .The accelerating voltage for SEM picture as 20.0 kv.

3 RESULTS AND DISCUSSION:

3.1 WEIGHT LOSS MEASUREMENT:

Weight loss data of mild steel in 1 molar HCI in the absence and presence of various concentrationsof inhibitors were obtained and are given in table 2. Inhibitors efficiencies were calculated accordingto following equation.

%IE =w0−wcorr

wcorr.

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NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

Wcorr and W0 are weight loss of mild steel in presence and absence of inhibitors respectively. Theresults showed that the inhibitor efficiencies increase with increasing the concentration of inhibitors.The results obtained from the weight loss measurement were in good agreement with thoseobtained from electrochemical measurements.

Inhibitor Concentration(ppm)

Weightloss(mg)

Surfacecoverage

Inhibitionefficiency (%E)

Blank - 235 - -5-Phenyltetrazole

100 61 0.7404 74.04200 32 0.8638 86.38300 28 0.8808 88.08400 21 0.9106 91.06500 11 0.9531 95.31

Table 2: The weight loss parameter obtained for mild steel in 1 M HCl containing differentconcentrations of 5- Phenyl tetrazole.

3.2 ADSORPTION ISOTHERM:

In corrosion field Adsorption isotherm provides basics information regarding interaction between theinhibitors molecules and metal surface [10].To find suitable adsorption isotherm in the present study,several commonly used isotherms were tested, among which Langmuir adsorption isotherms werefound to fit well with experimental data. Assumption of Langmuir relates the concentration of theadsorbate in the bulk of the electrolyte (C) to the degree of surface coverage (θ) according toequation: C/θ=1/K +C, where K is equilibrium constant of adsorption. The graph of C/θ vs Cobtained straight line with R2 value obtained varied close to unity confirming the validity of thisapproach .The slop of the straight line was almost close to unity, suggesting that adsorbed moleculeformed monolayer on mild steel surface.

Free energy of the adsorption (∆G0ads ) can be calculated using∆G0ads =-RT ln(55.5 kads)

Fig 1: Langmuir isotherm plot for adsorption of 5-Phenyl tetrazole on mild steel surface in 1M HCl.

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NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

Generally, value of ∆G0ads up to -20 kjmol-1 are associated with physisorption while those around -40kjmol-1 or higher are associated with chemisorptions. In present case the value was -29.34. Whichwas lower than -40 kj mol-1 but higher than -20 kj mol-1 indicating that the adsorption was neithertypical physisorption nor chemisorption but it was complex mix typed. Thus in present caseadsorption of inhibitor molecule on the mild steel involved both physisorption and chemisorptionsbut physisorption was the predominant mode of adsorption. The negative value of ∆G0ads indicatedthe spontaneous adsorption of inhibitors on the surface of the metal [11,12]

4 ELECTROCHEMICAL MEASUREMENTS:

4.1 OPEN CIRCUIT POTENTIAL (OCP) CURVES:

The potential developed on the mild steel electrodes relative to the potential of the referenceelectrodes is term as open circuit potential. The stabilization of OCP is essential before performingelectrochemical measurement .The variation of OCP of the working electrodes with respect to timein 1 molar HCI in absence and presence of inhibitors is shown in fig 2. The OCP curves givesstraight line in absence and presence of inhibitors, indicating that steady state potential has beenestablished after 30 min. immersion. It can be observed from OCP curves that in presence oftetrazole , the steady state potential ( Ecorr) shifted towards more positive direction without changingcommon feature of the OCP vs. time curves indicative that a physical barrier form between metaland inhibitors.

Fig 2: Open circuit potential diagram for mild steel in 1 M HCl without and with differentconcentrations of 5-Phenyl tetrazole.

4.2 POTENTIODYNAMIC POLARISATION STUDIESThe polarization behavior of mild steel in 1 M HCI in the absence and presence of differentconcentration of inhibitors are shown in fig.3.

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NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

Electrochemical parameters such as corrosion current (icorr), corrosion potential (Ecorr), and Tafelslopes constant βa and βc calculated from Tafel plots are given in table3. From the evaluated icorrvalue, η% can be calculated using the relation η% = i0−icorr

i0.where i0 and icorr are the corrosion

current densities in the absence and presence of inhibitors. From the table and figure, it is clear thatin the presence of tetrazole there was remarkable decrease in icorr value by shifting both anodic andcathodic Tafel slopes towards low current densities [13]. It was further confirmed that the shape ofpolarization curves were similar in absence and presence of inhibitors, suggesting that 5-phenyltetrazole inhibited mild steel corrosion by simply adsorbing on the mild steel surface withoutchanging the mechanism of mild steel dissolution[14]. An inhibitor can be classified as anodic,cathodic or mix type depending upon the displacement in Ecorr value. If the displacement in Ecorr forthe inhibited and uninhibited solution is more than 85mv it can be classified as cathodic or anodictype. But the displacement in Ecorr is less than 85 mv then it can be classified as mix type. Since themaximum displacement for studied compound was 21mv indicating that tetrazole is mixed typeinhibitors [15].

Fig 3: Polarization curve of mild steel in the absence and presence of 5-Phenyl tetrazole.

AcidMedium

Concentration(ppm)

-Ecorr(mv)

Icorr(A/cm2)

βa(v/dec)

βc(v/dec) IE %

1 M HCl

- -470.0 548.0 86.60 e-3 171.4 e-3 -100 -466.0 133.0 68.20 e-3 133.9 e-3 75.73200 -462.0 71.0 61.20 e-3 129.1 e-3 87.04300 -488.0 67.30 67.40 e-3 156.8 e-3 87.72400 -491.0 41.70 74.50 e-3 171.1 e-3 92.39500 -491.0 36.90 66.80 e-3 164.8 e-3 93.27

Table 3: Tafel polarization parameters for mild steel in 1 M HCl in absence and presenceof 5-Phenyl tetrazole.

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NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

4.3 SURFACE STUDIES:

4.3.1Scaning Electron microscope (SEM) studies

5-phenyl tetrazole forms protective film on surface of mild steel is further supported by SEMmicrograph of the mild steel surface obtained after immersion in 1 mol HCl for 24 hours in absenceand presence of 500ppm of 5-phenyl tetrazole. Figure [3a] represents the surface of mild steelwithout any addition. From figure [3b] it can be visualized that the specimen surface was rough andstrongly damaged in the presence of acid solution. Figure [3c] shows SEM micrographs of the mildsteel surface immersed in1M HCI containing 500 ppm of inhibitors. It can be concluded that extentof damaged to the mild steel surface was small and rate of corrosion was greatly reduced inpresence of inhibitors. This is due to formation of protective surface film on mild steel, which act asbarrier and was responsible for inhibition of corrosion.

Fig.3 SEM micro graphs of mild surface (a) before immersion in 1 M HCl, (b) after one dayimmersion in 1 M HCl and (c) after one day of immersion in 1 M HCl+500 ppm of 5-Phenyltetrazole.

4.3.2 Energy Dispersive X ray spectroscopy (EDX) studies.

To support weight loss and electrochemical studies, EDX spectra were collected from mild steel inthe presence and absence of 500 ppm inhibitors. Figure 4(a) shows EDX spectra of polished mildsteel surface with the characteristic peak for Fe. From fig.4[b] it is clear that the EDX spectra inabsence of 5-phenyl tetrazole shows characteristic signal for Fe, Mn, Cr, O and Cl due to damagecaused by 1 M HCl. However in presence of tetrazole the EDX spectra shown in fig.4[c] indicatessignal for nitrogen, confirming the presence of this element on surface, which could be due toadsorption of studied inhibitors on mild steel surface. One can also observe that the damage causeby 1M HCL is curtailed by inhibitors.

a) Polished surface of mildsteel

b) Mild steel in 1M HCl

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NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

Fig.4 EDX spectra of a) Polished surface of mild steel b) Mild steel in 1 M HCl c) Mild steel +500 ppm of 5-Phenyl tetrazole.

5. MECHANISM OF INHIBITION:

The inhibition effect of tetrazole derivatives on corrosion of mild steel in 1 M HCI solution may beattributed to the adsorption of this compound to the metal solution interface [16]. The extent ofadsorption of the inhibitors depends on the nature of metal, chemical structure of inhibitors, natureof electrolyte and temperature. Adsorption on the metal surface was suggested to be via the activecenter present on inhibitors molecule and relies on their charge density [17, 18].

In case of 5-phenyl tetrazole, the inhibition effect is due to interaction of π electron of phenyl andtetrazole ring as well as the presence of electron donor nitrogen through which it forms a bond withvacant d- orbital of the atom of the metal at the interface.

6. CONCLUSION:

The corrosion behavior of mild steel in 1 M HCI in absence and presence of tetrazole compoundwas investigated using the weight loss, open circuit potential and potentiodynamic polarizationtechnique and surface analytical techniques. From the result obtained the following conclusion canbe drawn:1. Tetrazole exhibited good inhibition efficiency and shows maximum efficiency at 500ppm.

2. There was good agreement between weight loss and electrochemical techniques to determinethe efficiency of corrosion inhibitors.

3 The data obtained from weight loss technique for the studied inhibitor fit well in to Langmuiradsorption isotherm.

4. Polarization studies showed that 5-phenyl tetrazole as mixed inhibitor

5. The surface morphology techniques showed that the mild steel specimen had smoother surfacesin the presence of inhibitors due to formation of protective film of adsorbed inhibitors on the metalsurface which prevented corrosion.

c) Mild steel + 500ppm inhibitors

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NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

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2. M.M.Solomon, S.A.Umoren, I .I. Udosoro and I .I. Udoh, Corrosion sci.2010, p.52, 1317.

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4. J. Ishwara, D.P.vijaya (2012) “A study of Aluminium corrosion inhibition in acid medium byantiemetic drugs’’ .springer 64 (4-5):pp.377-384.

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7. Ren Y, Luo Y, Zang K,Zhu G, Tan X,Lignine “tetrapolymer for inhibition of mild steel in 10%hydrochloric acid medium”. Corrosion science,50,2008,p.3147.

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solution”. International journal of current research in chemistry and pharmaceuticalsciences,vol.3 issue 12-2016.

9. Batool Akhlaghinia and Soodabeh Rezazadeh. “A novel Approach for Synthesis of 5-substituted -1H—tetrazole”.J.Baz.chem.soc.vol.23,no12,2197-2203,2012.

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11. j.,Shukla, K.S.Pitre, “Electrochemical behavior of brass in acid solution and the inhibitoreffect of imidazole” ,corrosion Rev., 2002 ,20(3), pp.217 -230.

12. Eno E.Ebenso, Ibe B.Obot, L.C. Murulana , “Quinoline and its derivatives as effectivecorrosion inhibitors for mild steel in acidic medium”,Int.j.Electrochem.sci.5(2010) pp. 1574-1586.

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NIGIS * CORCON 2017 * 17-20 September * Mumbai, IndiaCopyright 2017 by NIGIS. The material presented and the views expressed in this paper are solely those of the author(s) and do not necessarily by NIGIS.

15. M.Behpour, N.Mohammad, E.Alian, “Electrochemical and mass loss investigation of newSchiff base as corrosion inhibitor for mild steel”. J.iron steel Res.int, 21(2014), pp121-124.

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18. I.Ahamad and M.A.Qurashi, “Bis(benzimidazole -2-yl)disulfide , an efficient water solubleinhibitors for corrosion of mild steel in acid media” . Corrosion science vol.51, no.9 pp2006-2013,2009.