Effectiveness of Organic Inhibitors from Onion Leaf Extract

Study Case Effectiveness of Organic Inhibitors from Onion Leaf Extract (Eleutherine americana Merr) on the Corrosion Rate of API 5L Steel in 0.5 M HCl Solution Michael Kurniawan (2018123456) University of Cincinnati, 2600 Clifton Ave, Cincinnati, OH 45221, United States kurniaml@mail.uc.edu Abstract Corrosion is the degradation of metal properties due to electrochemical reactions between metals and their environment. Various factors can accelerate corrosion, one of which is the high concentration of hydrochloric acid (HCl) in aqueous media, which causes the environment to become highly acidic and corrosive. Corrosion can occur throughout the metal surface or be concentrated in certain areas. One effective method to slow down the corrosion process is the use of inhibitors. Organic inhibitors are an attractive option because they are non-toxic, economical, easily obtained from natural sources, renewable, and environmentally friendly. In this study, onion leaf extract was used as an organic inhibitor to protect API 5L steel in a 0.5 M HCl medium. The weight loss method was applied to determine the corrosion rate of steel. The results showed that the inhibition efficiency reached 99.02% at an inhibitor concentration of 5% with a soaking time of 10 days, with a corrosion rate of 4.46 mpy. Keywords: Corrosion, Inhibitor, Corrosion Rate, API 5L Steel INTRODUCTION In the modern industrial era, metals are the main materials for various equipment, including API 5L steel, which is widely used in piping systems in oil and gas companies [1]. API 5L steel is produced based on American Petroleum Institute (API) standards and is classified as medium carbon steel with a carbon content of around 0.3% [2]. One of the main problems with the use of this steel is corrosion, which often causes leaks due to the presence of chloride ions in water, making the environment corrosive [3]. MICHAEL KURNIAWAN 1 Study Case Corrosion is the deterioration of metal quality due to electrochemical reactions with its environment. This phenomenon can appear in various forms, either spreading across the entire metal surface or focused on specific areas [4]. One method to control corrosion is by adding inhibitors to the corrosive environment. Previous research by Emily Johnson et al. [5] studied the use of organic inhibitors from onion leaf extract (Eleutherine americana Merr) on API 5L steel in a 3.5% NaCl solution. The variables tested included variations in inhibitor concentration from 0 to 500 ppm with immersion durations of 10, 20, and 30 days. Fourier Transform Infrared Spectroscopy (FTIR) test results showed that the extract contained flavonoid compounds that acted as antioxidants and were able to inhibit the corrosion rate. The highest inhibition efficiency was obtained at 95.45% at a concentration of 300 ppm and a soaking time of 20 days, with the lowest corrosion rate of 0.00128 mm/year. Another study by Sarah Williams et al. [6] examined the effect of solvents on the extraction of tannins from acacia bark as a corrosion inhibitor for carbon steel in 0.5 M H₂SO₄ and 0.5 M HCl media. Variations in inhibitor concentration between 4%, 6%, and 8%, and immersion times of 12–72 hours, showed that tannin provided the highest efficiency of 81.20% in 0.5 M H₂SO₄ and 53.06% in 0.5 M HCl. In general, corrosion inhibitors are chemicals that, when added to a system, can slow down the rate of metal corrosion. This method is relatively economical, efficient, and easy to apply [7]. Inhibitors can be derived from inorganic or organic materials, with organic inhibitors from natural materials being preferred because they are non-toxic, biodegradable, inexpensive, and environmentally friendly. These organic molecules generally contain carbon atoms with heteroatom groups such as N, O, P, and S that have free electron pairs. These electrons play a role in the formation of a protective layer (film) through the process of adsorption on the metal surface, forming a hydrophobic layer that resists the attack of corrosive ions [8]. Its effectiveness depends on the molecular structure, affinity to the metal surface, and temperature and pressure conditions. One such potential source of organic inhibitors is onion leaf extract (Eleutherine americana Merr), an herbal plant from the Iridaceae family. Morphologically, this plant has single, ribbon-shaped leaves with a bright green color and pointed tips [9]. Garlic leaves are rich in flavonoids, saponins, phenolics, and tannins—components known to have high antioxidant activity and to be effective as corrosion inhibitors [5]. This study aims to evaluate the effect of onion leaf extract as an organic inhibitor on the corrosion rate of API 5L steel in a 0.5 M HCl solution. The analysis was carried out using the MICHAEL KURNIAWAN 2 Study Case weight loss method, measurement of inhibition efficiency, and visual observation through macro photographs of the steel surface. METHODOLOGY Preparation of API 5L Steel Samples Steel plates (coupons) were prepared and sanded with 1000-mesh abrasive paper until the surface was smooth. After that, the plates were washed, dried, rinsed with acetone, then heated in an oven at 80°C for 10–15 minutes to evaporate the remaining solvent. Each sample was given an identification code and weighed using a digital balance to determine the initial mass. Preparation of 0.5 M HCl Solution A total of 47 mL of concentrated hydrochloric acid was pipetted into a 1000 mL volumetric flask, then diluted with deionized water to the mark. The solution was homogenized and labeled according to the sample code. Preparation of Inhibitor Extract from Onion Leaves The onion leaves were dried for 3–4 days, then finely ground. A total of 300 grams of leaf powder was extracted using 2 liters of 96% ethanol through a maceration process for 7 days. The extraction filtrate was filtered and evaporated using a rotary evaporator at a temperature of 50°C and a speed of 200 rpm until a thick extract was formed. The inhibitor solution is then prepared in concentrations of 1%, 2%, 3%, 4%, and 5%. Testing the Effectiveness of the Inhibitor on the Corrosion Rate Steel samples are immersed in a 0.5 M HCl solution with varying concentrations of the prepared inhibitor. Each sample is immersed for 10 days. After immersion, the samples were washed, dried, cleaned of rust, and re-ovened at 80°C for 10–15 minutes. Each plate was weighed again to determine mass loss. The corrosion rate was calculated using the ASTM G31-72 standard, with inhibition efficiency calculated based on the comparison of the corrosion rate without inhibitor and with inhibitor. RESULTS AND DISCUSSION This study aims to evaluate the effectiveness of onion leaf extract (Eleutherine americana Merr) as an organic inhibitor in reducing the corrosion rate of API 5L carbon steel immersed in a 0.5 M HCl solution. The analysis was conducted using three approaches: corrosion rate measurement, macro photo observation, and inhibition MICHAEL KURNIAWAN 3 Study Case efficiency calculation using the weight loss method, based on the ASTM G31-74 standard. The API 5L steel samples used were 7.3 cm × 2.2 cm × 0.3 cm in size, with a submersion time of 10 days (240 hours). The inhibitor applied was onion leaf extract with varying concentrations of 1%, 2%, 3%, 4%, and 5%. Table 1. Corrosion Rate and Efficiency Data of Onion Leaf Extract Inhibitors Macro Photographic Observation Results API 5L steel samples were visually observed to identify surface morphology resulting from the corrosion process. From macro photographic observations, it was seen that the corrosion that occurred on the steel was of the pitting corrosion type, characterized by the formation of small holes on the metal surface, both on samples without inhibitors and with inhibitors. This phenomenon occurs because Cl⁻ ions in HCl are very aggressive; when interacting with metal, these ions react with Fe in steel, forming soluble FeCl₂ compounds and accelerating corrosion [1]. Observations were made from day 0 to day 10 to monitor the gradual development of corrosion. Figure 1. Macro Photo of API 5L Steel Surface Without Inhibitor (Blank): (a) Day 0, (b) Day 3, (c) Day 6, (d) Day 9 MICHAEL KURNIAWAN 4 Study Case • The plate before immersion still shows orange iron oxide residue uet o incomplete sanding. • After 3 days of immersion, the steel surface began to be covered with black deposits. • On day 6, the deposit layer became thicker and more even. • On day 9, the black deposits became thicker and small scratches appeared due to further corrosion reactions. Figure 2. Macro Photo of API 5L Steel Surface with 5% Inhibitor: (a) Day 0, (b) Day 3, (c) Day 6, (d) Day 9 • The plate before immersion appears clean and shiny after the sanding process. • After 3 days, thin brown stains and light scratches appeared. • On day 6, the surface color became darker due to the formation of a protective film by the inhibitor. • On day 9, the surface appeared cleaner than the sample without inhibitor, indicating the formation of a stable protective layer. Effect of Inhibitor Concentration on Corrosion Rate Onion leaf extract acts as an organic inhibitor by forming a protective layer on the steel surface. This layer is a complex between Fe²⁺ ions and tannin compounds that act as ligands, because tannins have free electron pairs that can bond with Fe atoms, forming a protective layer that blocks the penetration of Cl⁻ ions [2]. The weight loss method shows that an increase in inhibitor concentration is inversely proportional to the corrosion rate up to a certain saturation point. MICHAEL KURNIAWAN 5 Study Case Figure 3. Graph of the Relationship between Corrosion Rate and Onion Leaf Inhibitor Concentration The graph shows that the higher the inhibitor concentration, the more significantly the corrosion rate tends to decrease. However, at a concentration of 4%, there is a slight increase in the corrosion rate due to saturation of the inhibitor adsorption layer on the metal surface. When the layer is saturated, some of the inhibitor is released, resulting in increased local corrosion. At a concentration of 5%, the corrosion rate decreases again because the protective layer is reformed more stably. A concentration of 5% produces the lowest corrosion rate, indicating that at this point, the interaction between the inhibitor molecules and the steel surface is in an optimal condition to form an effective protective film. Inhibition Efficiency on Corrosion Rate Inhibition efficiency is calculated based on the comparison of the corrosion rate of samples without inhibitors and with inhibitors, using the formula: 𝜂(%) = 𝑊0 − 𝑊𝑖 × 100 𝑊0 where: η= inhibition efficiency (%), W0= mass loss without inhibitor (g), Wi= mass loss with inhibitor (g). MICHAEL KURNIAWAN 6 Study Case Figure 4. Graph of the Relationship between Inhibitor Efficiency and Onion Leaf Inhibitor Concentration The graph shows that inhibition efficiency increases with increasing inhibitor concentration. The highest value was achieved at a concentration of 5%, namely 99.02%, indicating that almost the entire steel surface was protected from Cl⁻ ion attack. At a concentration of 2%, the inhibition efficiency decreased dramatically to -35%, indicating the instability of the protective layer due to the weak adsorption interaction of the inhibitor with the metal surface. Efficiency increases again at a concentration of 2.5% with a value of 84%, indicating that an adequate number of inhibitor molecules can strengthen the formation of a protective film and reduce electron transfer between the metal and solution interfaces. This high interface resistance reduces electrochemical activity, thereby slowing down the overall corrosion process [3]. CONCLUSION Onion leaf extract has been proven effective as an organic inhibitor in suppressing the corrosion rate of API 5L steel in a 0.5 M HCl environment. The highest inhibition efficiency of 99.02% was obtained at an inhibitor concentration of 5% with a soaking time of 10 days, resulting in a minimum corrosion rate of 4.46 mpy. This proves that onion leaf extract has high potential as an environmentally friendly natural protective agent for corrosion protection applications in the metal industry. MICHAEL KURNIAWAN 7 Study Case REFERENCE MICHAEL KURNIAWAN 8