_____________________________________________________________________________________________________________________________ Full Paper ECO-FRIENDLY INHIBITORS FOR EROSION-CORROSION MITIGATION OF API-Xϲϱ STEEL IN CO2 ENVIRONMENT _____________________________________________________________________________________________________________________________________________________ O.O. Ige Department of Materials Science and Engineering, Obafemi Awolowo University, Nigeria. ige4usa@yahoo.com M.D. Shittu Department of Materials Science and Engineering, Obafemi Awolowo University, Nigeria. K.M. Oluwasegun Department of Materials Science and Engineering, Obafemi Awolowo University, Nigeria. O.E. Olorunniwo Department of Materials Science and Engineering, Obafemi Awolowo University, Nigeria. L.E. Umoru Department of Materials Science and Engineering, Obafemi Awolowo University, Nigeria. ABSTRACT The study of chemical mitigation of erosion-corrosion of API- X65 Steel in a multiphase system containing brine, CO2 gas, and sand at different shear stresses with two eco-friendly inhibitors are reported. The inhibitors investigated are a commercial grade synthetic product and a natural inhibitor (Aloe vera). The mass loss, linear polarization, and scanning electron microscopy techniques were investigated. The results obtained show that both inhibitors maybe useful in oil and gas industry, the synthetic inhibitor have quantifiable advantage over the natural inhibitor. From the results obtained these inhibitors are expected to have credible technical performance and as such reduce considerably the adverse effects on health, safety, and environmental factors associated with inhibition in oil and gas industries. Keywords: Erosion-corrosion, Inhibitors, Multiphase system, Steel, Rotating cylinder electrode, and scanning electron microscopy. 1. INTRODUCTION The importance of corrosion inhibitors in the oil and gas industry is well established and cannot be underestimated. Corrosion inhibitors are known to prevent discharge of oil and gas through leakages to the environment (Obesekesere et al., 2002). They also play a significant role in internal corrosion control associated with oil and gas production and transportation (Taj et al., 2006). Due to rapid depletion and huge exploitation, future oil and gas productions are expected to occur more in remote areas. This will lead to increasing challenges relating to asset management, which includes; sand presence in production fluids and the shift towards deeper wells. All these may result in difficulties in maintaining the integrity of pipes and process equipment (Wang et al., 2005). In particular, there have been extensive studies of chemical inhibition of erosion-corrosion. Some of these studies have concluded that corrosion inhibitors are effective in controlling erosion corrosion mechanisms. The attention has been focussed on mechanisms of inhibition, inhibition efficiency, and material degradation phenomena, among others (McLaury et al., 1995; Schmitt, 2001; Ramachandra et al., 2005 and Wang et al., 2005). Research efforts have also been deployed to study the effectiveness of inhibitors in the presence of erosive flows and at different shear stresses (Neville and Wang, 2009). However, in the majority of these studies related to chemical mitigation of CO2 corrosion, the focus has been more on superior performance with little or no emphasis on the health, safety, and environmental factors (Chen and Chen, 2002). However national government of various countries have invoked tighter and stringent conditions due to more severe environmental constraints. Hence several attempts have been made to develop the chemistry that is considered green in nature (Obeyesekere et al., 2000; Killars and Finley, 2001; Chen and Chen, 2002). There is little previous work that investigated the performance of eco-friendly inhibitors in the erosion-corrosion control. Therefore, the aim of this work is to examine the behaviour of mild steel in the presence of a synthetic “green” chemistry based system and a natural product as corrosion inhibitors in a multiphase system containing brine, CO2 gas, and sand at different shear stresses. The data obtained are compared for their performance in order to determine the effectiveness of the inhibitors as candidates for inhibition in oil and gas industry. 2. MATERIALS AND METHODS 2.1. Materials The steel used in this study is as-received API 5L X65 carbon steel with Vickers hardness of 240 HV. The samples were cylindrical shaped with dimensions of 12 mm by 8 mm. The microstructure and chemical composition are as shown in Figure 1 and Table 1, respectively. 2.2. Media and Inhibitors Table 2 shows the chemistry of the process solutions was prepared according to the work of Hu et al. (2011). Two different corrosion inhibitors were studied. They are referred to as Aloe vera and inhibitor NA. The Aloe vera represents a natural inhibitor with green chemistry while the inhibitor NA is a commercially available, high shear eco-friendly CO2 – based inhibitor. The Aloe vera leaves were sliced open at the edges and the gel was squeezed out, sieved in order to obtain a clear concentrated semi- liquid. No water was added. The liquid is viscous, colourless, transparent, consists of water (98.5%), and polysaccharides (0.3%) (WHO, 1999). The polysaccharide composition was analysed by gas Ife Journal of Technology, Vol. 21(2), 43-48, 2012 43 1115-9782 © 2012 Ife Journal of Technology http://www.ijtonline.org