ISSN 1925-542X [Print] ISSN 1925-5438 [Online] www.cscanada.net www.cscanada.org Advances in Petroleum Exploration and Development Vol. 6, No. 2, 2013, pp. 56-59 DOI:10.3968/j.aped.1925543820130602.1829 56 Copyright © Canadian Research & Development Center of Sciences and Cultures Effciency Criterion of Corrosion Inhibitors of Carbon Steel in Seawater K. Habib [a],* [a] Materials Science and Photo-Electronics Lab., IRE Program, EBR Center KISR, P.O.Box 24885 SAFAT, Kuwait. * Corresponding author. Received 22 November 2013; accepted 23 December 2013 Abstract A criterion of the efficiency evaluation of corrosion inhibitors of metallic samples in aqueous solutions was proposed for the frst time.The criterion was derived based on calculating the limit of ratio value of the resistivity of carbon steel sample in inhibited seawater (ρ ins ) to the resistivity of the carbon steel sample in blank seawater (ρ s ). In other words, the criterion; lim (ρ ins / ρ s ) =1 will determine the efficiency of the corrosion inhibitor in the seawater when ρ ins becomes equal (decreases) to ρ s as a function of time of the exposure of the sample to the inhibited seawater. This criterion is not only can be used to determine the efficiency of different corrosion inhibitors, but also, the criterion can be used to determine the effciency of corrosion inhibitors with a wide range of concentrations in different aqueous solutions. In addition, the criterion can be applied under diverse test conditions with a predetermined period of inhibitor’s dosages. Key words: Efficiency of corrosion inhibitors; Resistivity; Carbon steel; Seawater Habib, K. (2013). Efficiency Criterion of Corrosion Inhibitors of Carbon Steel in Seawater. Advances in Petroleum Exploration and Development, 6(2), 56-59. Available from: URL: http://www.cscanada. net/index.php/aped/article/view/j.aped.1925543820130602.1829 DOI: http://dx.doi.org/10.3968/j.aped.1925543820130602.1829 INTRODUCTION In the oil production, water and acidic gases, i.e., H 2 S and CO 2 , are co-produced with the oil. The acidic gases are known to associate with a variety of corrosion damage to the surface facilities leading to costly failures. Also, the acidic gases cause a reduction in the service life of equipment. One of the known method of protection against corrosion damage in oil production is the usage of corrosion inhibitors [1] . Corrosion inhibitors are organic and inorganic materials that are usually added to a fluid source (liquids or gages) in small amounts on a frequent basis to reduce or to stop corrosion. The evaluation of corrosion inhibitors of exposed metals has been studied by many investigators [2-9] . Some studies of the corrosion inhibitors were dependent on electrochemical techniques like linear polarization, polarization resistance, Tafel plot, potential dynamic curve, and electrochemical impedance spectroscopy [10] . In contrast, other studies were relied on only the weight loss method for evaluation of the corrosion inhibitors [10] . In the present work, a criterion of the efficiency evaluation of corrosion inhibitors was developed. The criterion was plotted based on obtained resistivity data of the author’s previous works [11-13] . The resistivity value of the corrosion inhibitor can be measured as the follows [11-13] : ρ = RA/ U total (1) Where, ρ is the electrical resistivity of the formed oxide flm, Ohm-cm; R is the dc resistance of the formed oxide flm, Ohm; A is the exposed surface area of the sample to solution, 37.5 cm 2 ; U total is the total thickness of the formed oxide film, which can be obtained by holographic interferometry, a noncontact technique, μcm. U total can be determined as the following [11-13] : U total = Nλ/sin α + sin β (2) Where, N is the number of fringes;