165

Int. J. Mech. Eng. & Rob. Res. 2014 Ghanshyam Das, 2014

INHIBITING EFFECTS OF ORGANIC INHIBITORON CORROSION OF STEEL IN 3.5% BRINE

SOLUTION

Ghanshyam Das1*

*Corresponding Author: Ghanshyam Das,gsdnifft@gmail.com

The experiment for API grade steel has been carried out by using weight loss measurementtechnique. All the experiments were carried out in an autoclave at varying temperature and afixed partial pressure of carbon dioxide. The different concentration of imidazoline as organicinhibitor has been added in the solution to know the inhibition effect on the metal surface. Theresults indicated that addition of 40 ppm of inhibitor showed the higher efficiency due to theformation of more adhered and protective film over the metal surface. The exposed sampleswere characterized by using various techniques such as x-ray photoelectron spectroscopy andscanning electron microscopy.

Keywords: Imidazoline inhibitor, Brine solution, Autoclave, SEM, FTIR

INTRODUCTIONInhibitors are the chemical substances thatreact with a metallic surface exposed in thecorrosive environment. Usually, inhibitors areused to protect the metallic surface by forminga corrosion film. These inhibitors are often workby adsorbing themselves on the metallicsurface, and thus preventing the surface forfurther corrosion by forming a protective film.It may slow down the corrosion process eitherby increasing anodic or cathodic polarizationbehavior or by reducing diffusion of ions to themetallic surface. The presence of sufficient

ISSN 2278 – 0149 www.ijmerr.comVol. 3, No. 3, July 2014

© 2014 IJMERR. All Rights Reserved

Int. J. Mech. Eng. & Rob. Res. 2014

1 Material Science & Metallurgical Engineering, National Institute of Foundry and Forge Technology, Hatia, Ranchi 834003, India.

concentration of organic inhibitors affects theentire surface of a corroding metal and thus itis designated as film forming inhibitor thatprotects the metal by forming a hydrophobicfilm on the metal surface. The effectiveness ofthese inhibitors depends on the chemicalcomposition, molecular structure, and theiraffinities for the metal surface. Since, filmformation is an adsorption process and itdepends on temperature and pressure whichis an essential parameter of the system. Theorganic inhibitors are adsorbed according topresence of ionic charge of the inhibitor and

Research Paper

166

Int. J. Mech. Eng. & Rob. Res. 2014 Ghanshyam Das, 2014

the charge on the surface. Cationic inhibitors,such as amines and anionic inhibitors such assulfonates, are adsorbed preferentiallydepending on whether the metal is chargednegatively or positively. The strength of theadsorption bond is the dominant factor forsoluble organic inhibitors. Howeverdetermination of optimal concentration forspecific inhibitor in a certain corrosiveenvironment is a challenging task. Forexample, a concentration of 0.05% sodiumbenzoate is effective in 3.5% sodium chloridesolution at a pH value of 7.5. There arenumerous chemical inhibitors are availablethat exhibit inhibitive properties but only feware actually used in practice. This may be dueto fact that the desirable properties of aninhibitor usually extend beyond those simplyrelated to metal protection. Also, the otherparameters such as avaibility, toxicity, cost andenvironmental friendliness are of considerableimportance.

Corrosion Costs and PreventiveStrategyDespite many developments in corrosionresistant alloys over the past few decades,carbon steel still constitutes an estimated 80-90% of the material used in the oil industry. Itis usually the most cost effective option, beinga factor of 3 to 5 times cheaper than stainlesssteels. Yet its corrosion resistance is poor inaggressive environments, and the costsavings can only be realized by adding asuitable corrosion inhibitor to the environmentor to the steel surface. Inhibitors are used in awide range of applications such as oil and gasexploration and production industry, thepetroleum refining industry, the chemicalindustry, heavy industrial manufacturing

industry, water treatment facilities, and theproduct additive industries. A particularadvantage of corrosion inhibition is that it canbe implemented in situ without disrupting aprocess. The largest consumption of corrosioninhibitors is in the oil industry, particularly inthe petroleum refining industry. The totalconsumption of corrosion inhibitors in theUnited State has doubled from approximately$600 mn in 1982 to nearly $1.1 bn in 1998.

Inhibitor EfficiencyA corrosion inhibitor is a chemical substancethat, when added in small concentration to anenvironment, effectively decreases thecorrosion rate. The efficiency of that inhibitoris thus expressed by a measure of thisimprovement known as inhibitor efficiency andexpressed as;

Inhibitor efficiency (%) = 100 x (CRuninhibited –CRinhibited)/CRuninhibited

where: CRuninhibited = corrosion rate in uninhibitedcondition and CRinhibited = corrosion rate of theinhibited condition. In general, the efficiencyof an inhibitor increases with an increase ininhibitor concentration, e.g., a typically goodinhibitor may give 95% of inhibition at aconcentration of 0.008% and 90% at aconcentration of 0.004%.

ExperimentalThe material used in the current study wasobtained in a pipe form. The as-receivedmaterials was cut into the rectangularspecimen of dimension 20 mm x 12 mm x 2.5mm with a center hole of diameter 1.5 mm atthe top edge of each specimen to facilitate thesuspension inside of the autoclave of capacity2.2 liter. The faces of the sample were initiallycoarse grounded on a SiC belt grinder

167

Int. J. Mech. Eng. & Rob. Res. 2014 Ghanshyam Das, 2014

machine then consequently machine polishedin the successive grades of emery papers(220, 400, 600 800 and 1000). The initialweight and area of the sample was measuredusing digital weighing machine upto anaccuracy of four digits. Four differentexperiments were carried out at differenttemperature range (30 °C-120 °C) in anautoclave with a constant partial pressure of100 psi. All the experiments were carried outfor 96 hours in a multiphase dynamic flow loopmachine with a constant fluid velocity of 1.5 m/s. The oxygen solubility of the system wasmaintained below 40 ppm by pouring argongas inside the vessel. In the beginning of thetest, the actual temperature of the machine wasset as 30 °C, 60 °C, 90 °C and 120 °Crespectively and separately and then createdthe actual partial pressure of carbon dioxideby releasing the carbon dioxide gas inside theautoclave. After 96 hours of exposure, thesamples were taken out from the autoclavewashed in distilled water, rinsed in acetone andthen dried in air. After cleaning, the couponswere again re-weighed and finally thecorrosion rate of the sample was measured inmills per year. The same process wasrepeated with addition of differentconcentration of imidazoline inhibitor in thesolution. Also, the morphology of the exposedsamples was analyzed using differentcharacterization techniques such as FourierTransform Infra Red (FTIR), ElectrochemicalImpedance Spectroscopy (EIS) and scanningelectron microscopy.

RESULTS AND DISCUSSIONThe weight loss graph indicates that thecorrosion rate of steel increases withincreasing temperature upto 90 °C as shown

in Figure 1. This may be due to formation ofporous non-protective film on the metal surfaceresults in continuous dissolution in the solution.Beyond this temperature, the corrosion rateagain fall down due to formation of dense andadhered layer of oxide iron carbonate film onthe metal surface. At higher temperature theformed iron carbonate film is very dense andcompact on the surface results in slowercorrosion rate. The addition of inhibitors in thesolution indicated effectively decrease in thecorrosion rate as shown in Figure 1 due toformation of more dense and protective filmon the metal surface. The addition of inhibitoron the metal surface showed betterperformance of protectiveness at all theconcentrations. However, the maximumprotection was observed at the concentrationof 40 ppm where the curve becomes almostsaturated and occupies more space assemicircle (Figure 3). This is due to theformation of dense and adhered protective filmon the metal surface. The FTIR pattern inFigure 2 indicated the presence of nitrogenbased amines in the base inhibitor. EIS patternalso indicted the formation of protective filmon the metal surface as the concentration ofinhibitor increases upto 40 ppm. In the rangeof 40-50 pm of imidazoline inhibitor had shownbetter formation of protective film (Figure 3).The SEM micrographs of exposed samplewithout application of inhibitor showed theformation and propogation of cracks at thecenter as shown in Figure 5, while in additionof 40 ppm inhibitor no cracks observed asclearly seen in Figure 6. This may be due toformation of dense and adhered filmpredominantly forming over the surface andprotective in nature.

168

Int. J. Mech. Eng. & Rob. Res. 2014 Ghanshyam Das, 2014

Elements Wt%

C 0.16

Mn 1.25

Si 0.31

S 0.003

P 0.004

Cr 0.05

Mo -

Cu 0.14

Table 1: Chemical Composition of asReceived Material (wt%) Obtained

by Mass Spectroscopy

Figure 1: Corrosion Rate Patternwith and Without Inhibitor

Figure 2: FTIR Pattern of Base ImidazolineInhibitor

Figure 3: EIS Patterns of Steelwith and Without Inhibitor

Figure 4: Bode Patterns of API X-52Grade Steel

Figure 5: SEM Micrograph of ExposedSample Without Inhibitor

169

Int. J. Mech. Eng. & Rob. Res. 2014 Ghanshyam Das, 2014

Acidic Medium by 2, 20-bis(benzimidazoles)”, Allied SurfaceScience, Vol. 252, pp. 8178-8184.

2. Al-Juaid S S (2011), “Inhibition ofCorrosion of Carbon Steel 1018 in AcidMedium with Ethoxylated AliphaticAlcohols”, Chemistry and Technology ofFuels and Oils, Vol. 47, No. 1, pp. 58-65.

3. Ashassi-Sorkhabi H, Majidi M R andSeyyedi K (2004), “Investigation ofInhibition Effect of Some Amino AcidsAgainst Steel Corrosion in HCl Solution”,Applied Surface Science, Vol. 225,Nos. 1-4, pp. 176-185.

4. Efird K D and Jasinski R (1989), “Effectof Crude Oil on Corrosion of Steel inCrude Oil/Brine Production”, Corrosion,Vol. 45, No. 2, p. 165.

5. Frenier W, Hill D and Jasinski R (1994),“Corrosion Inhibitors for Acid Jobs”,Oilfield Review, Vol. 1, No. 2, p. 15.

6. Jasinski R (1986), “Corrosion of Low AlloySteel in Crude Oil/Brine/CO2 Mixtures”,Proc., The Electrochemical Society:Surfaces, Inhibition and Passivation,Vol. 86, No. 7, pp. 139-148, Princeton.

7. Kriel B G, Lacey C A and Lane R H (1994),“The Performance of Scale Inhibitors inthe Inhibition of Iron Carbonate Scale”,SPE Formation Damage ControlSymposium, February 7-10, SPE-27390-MS, Lafayette, Louisiana.

8. Krueger J (1982), “Passivity andBreakdown of Passivity”,Electrochemistry in Industry, U Landau,E Yeager and D Kortas (Eds.), Ch. 5,pp. 317-330, Plenum Press, New York.

Figure 6: SEM Micrograph of ExposedSample with 50 ppm Inhibitor

CONCLUSIONThe corrosion rate of steel without inhibitorhad shown higher corrosion rate whileaddition of imidazoline inhibitor in all theconcentrations reduced the corrosion ratesignificantly. The more protection has beenobserved at 40 ppm of imidazoline due toformation of dense and adhered layer ofprotective film on the metal surface. Ataggressive temperature the layer formed onthe surface dissolving continuously and thereaction rate becomes faster and shownhigher corrosion rate while at highertemperature the iron carbonate film form inpresence of nitrogen based imidazolineinhibitor which is very dense and compact onthe metal surface results in slower corrosionrate.

REFERENCES1. Abboud Y, Abourriche A, Saffaj T,

Berrada M, Charrouf M, Bennamara A,Cherqaoui A and Takky D (2006), “TheInhibition of Mild Steel Corrosion in

170

Int. J. Mech. Eng. & Rob. Res. 2014 Ghanshyam Das, 2014

9. Lebrini M, Lagrenée M, Vezin H, TraisnelM and Bentiss F (2007), “Experimentaland Theoretical Study for CorrosionInhibition of Mild Steel in NormalHydrochloric Acid Solution by Some NewMacrocyclic Polyether Compounds”,Corrosion Science, Vol. 49, No. 5,pp. 2254-2269.

10. Neemla K D, Saxena R C andJayaraman A (1992), “Corrosion InhibitorStudies on Steels in Hydrochloric Acid”,Corrosion Prevention and Control ,Vol. 6, pp. 69-76.

11. Ozcan M (2008), “AC ImpedanceMeasurement of Cystine Adsorption atMild Steel Interface as Corrosion Inhibitor”,

Journal of Solid State Electrochemistry,Vol. 12, pp. 1653-1661.

12. Poling G W (1967), “Infrared Studies ofProtective Films Formed by AcetylenicCorrosion Inhibitors”, Journal of TheElectrochemical Society , Vol. 114,pp. 1209-1214.

13. Smith S N (1993), “A ProposedMechanism for Corrosion in Slightly SourOil and Gas Production”, Poc. 12th Int.Corrosion Congress Held in September19-23, NACE International, Houston, TX.

14. Treseder R and Tuttle R (1998),“Corrosion Control in Oil and GasProduction”, Item No. 37741, NACE,Houston.