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Corrosion and Corrosion Inhibition Behavior of N80 and P110 Carbon Steels in CO2-Saturated Simulated Formation Water by Rosin Amide Imidazoline P. C. Okafor,†,‡ C. B. Liu,† Y. J. Zhu,† and Y. G. Zheng*,† †
State Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences, 62 Wencui Road, Shenyang 110016, Liaoning Province, PR China ‡ Corrosion and Electrochemistry Research Group, Department of Pure and Applied Chemistry, University of Calabar, P. M. B. 1115, Calabar, Nigeria ABSTRACT: The corrosion and corrosion inhibition of N80 and P110 carbon steels (CS) in CO2-saturated simulated formation water by rosin amide imidazoline (RAIM) was studied using electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The results indicate that N80 CS performs better than P110 CS with RAIM at lower temperature and P110 CS at higher temperatures. Inhibition efficiency increased with increase in RAIM concentration and temperature. The data suggest that RAIM functioned as inhibitor via a mixed-inhibitor mechanism and the inhibition process is attributed to the formation of a chemically adsorbed film of RAIM on the surface of the metal via its polycentric adsorption sites. Morphological studies of the carbon steel electrode surface were undertaken by scanning electron microscope (SEM) and atomic force microscopy (AFM).
1. INTRODUCTION Carbon dioxide corrosion of steel pipelines is a complex process due to the variety of corrosion active species present in the solution and has been a serious problem in the oil and gas industry for several years causing losses of millions of dollars per year. Carbon steel is widely used in the infrastructure for the oil and gas industry, despite its low corrosion resistance. This is probably due to its well developed technology and cost-effective characteristics. To reduce the aggressiveness of CO2-saturated solutions on carbon steel, inhibitors are used and acknowledged to be the most cost-effective and flexible means of corrosion control in the oil and gas production industry.15 Organic substances such as heterocyclic compounds containing one or more N, O, and S atoms can adsorb on the metallic surface and can act by blocking the active sites or generating a physical barrier to reduce the transport of corrosive species to the metal surface. One class of organic substances which has proven to be most effective in CO2saturated systems and widely applied for protecting CO2 corrosion of oil and gas pipelines is the imidazolines.314 This is probably due to their high inhibition effectiveness and availability.14,15 Imidazoline derivatives are also considered to be “green” corrosion inhibitors, due to their biodegradability which will satisfy the environmental requirements that are currently imposed on the development of cleaner chemical inhibitors.16 Imidazoline derivatives are an extensive group of nitrogen based organic compounds that behave as cationic surfactants, depending on the nature of hydrocarbon or substituents groups attached to the carbon or nitrogen atoms of the imidazoline ring.16 The effectiveness of these compounds as corrosion inhibitors have been ascribed to the adsorption of the molecules on the metal surface by the formation of an ironnitrogen coordination bond, by a p-electron interaction between the p-electron in the headgroup and iron, and by Coulombic attraction.13 r 2011 American Chemical Society
Figure 1. Structure of RAIM.
However, studies on a series of imidazoline derivatives have indicated that the reactivity of imidazoline derivatives is located mainly on the nitrogen atoms to be strongly bonded to the surface16 thereby giving them their characteristic high inhibition efficiencies. It has also been reported that their inhibition efficiencies and the inhibition mechanisms are dependent on the temperature and flow velocity as well as composition of the aggressive environment,11,13,1719 but these are still to be further explored. We have reported on the effectiveness of some imidazoline derivatives as inhibitors for carbon steel in CO2-saturated solutions and in sulfuric acid.5,1013,15 The high inhibition efficiencies obtained from these studies impelled us to test more derivatives of this class of compounds. In continuation of an extensive project being carried out in our laboratories on the development of corrosion inhibitors with high effectiveness and efficiency for the oil and gas pipeline steels, under various experimental conditions, we present here the Received: November 30, 2010 Accepted: April 27, 2011 Revised: March 29, 2011 Published: April 27, 2011 7273
dx.doi.org/10.1021/ie1024112 | Ind. Eng. Chem. Res. 2011, 50, 7273–7281
Industrial & Engineering Chemistry Research
ARTICLE
Table 1. Chemical Composition of the N80 and P110 Carbon Steels element composition (wt %)
C
Si
Mn
P
S
Al
Cu
Nb
Ni
N80
0.52
0.23
1.50
0.011
0.008
0.01
0.07
