ABSTRACT

In this study, different concentrations of C6H5NH2 (Aniline) were employed for investigating its corrosion inhibition of stainless steel in 0.5 M HCl. Corrosion rate measurements at 28°C, 45°C and 60°C were obtained from a linear sweep voltametry instrument and analyzed for inhibition efficiency and apparent activation energy in the presence and absence of C6H5NH2. Results showed that C6H5NH2 generally exhibited excellent inhibition effects on stainless steel corrosion at the higher temperatures, i.e. the 45°C and 60°C, at which the self-protectiveness of the stainless steel metal appears to breakdown. In contrast, the stainless steel metal exhibited self protection in the presence and absence of C6H5NH2 at the low temperature of 28°C, such that very low inhibition effects of aniline appears to be required at this temperature. Thus, while maximum inhibition efficiency (?) = 23.13% at 28°C by the 0.086 M C6H5NH2, inhibition efficiency was as high as ? = 96.00% by 0.043 M C6H5NH2 at 40°C and ? = 95.58% by the 0.107 M C6H5NH2 at 60°C on stainless steel corrosion in the HCl test-medium. Apparent activation energy analyses showed that this thermodynamic quantity decreased in values from the uninhibited, Ea = 100.37 kJ/mol, to the excellently inhibiting 0.107 M C6H5NH2 for which Ea = 6.30 kJ/mol. The implications, of these results, on the temperature dependency of C6H5NH2 corrosion inhibition performance as well as on the dominance of chemisorption adsorption mechanism by this chemical inhibitor on the stainless steel metal were detailed in the study.

INTRODUCTION

Metal loss and deleterious attack that lead to localized corrosion are a major challenge to the operations of petrochemical, refining and chemical industries. Yet more catastrophic is the insidious nature of corrosion that leads to spontaneous loss of load carrying capacity of metals in service. Such environment induced damage results in loss of production man-hours, spillage, pollution, health risks, disposal burdens, and in some cases litigation.1-3 All these translate to enormous cost to the economy. In fact, metallic corrosion cost to the U.S. economy is currently put at a whopping 3.1 percent of gross domestic product (GDP).4 These, invariably, put a massive negative strain on the economy.

Chlorides, especially that which could not be removed by the desalters in the petroleum refining process,5 forms hydrochloric acid (HCl) that elevates corrosion rate. Apart from this, hydrogen chloride is also a multipurpose raw material used in industrial materials treatments such as pickling, acid cleaning, descaling, and oil well acidizing.6-7 This makes the metallic substrate exposed to the acid treatment susceptible to acidic corrosion attacks.6 As indicated in studies,8 more than a third of stainless steel production is employed for the chemical and energy industries in applications including canals/components in burners/furnaces for nuclear reactors, heat converters, tubes for oil industries, and components materials in paper industries.8-10 Stainless steel corrosion in HCl is quite complicated because of its inherent ‘self healing’ property by which a passive film rapidly forms on the metal when exposed to environmentally-induced attacks, including acidic attacks. In spite of this, however, it is still difficult to predict the outcome of stainless steel-HCl reaction at slightly elevated temperatures. For instance, while specific grade of stainless steel (e.g. the 316 Fe-Cr-Ni) is regarded ”marine grade”, due to excellent corrosion resistance, this grade is still not resistant to warm chloride environment, even the near neutral but warm seawater, wherein it is prone to pitting/crevice corrosion.8 That this property could constitute serious degradation concerns in industrial applications such as stainless steel reactors, agitators, pumps, pressure vessels and oil drains that undergo exposures to HCl at varying temperature and concentrations, constitutes motivation for this study.

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