Electrochemical evaluation of expired antirheumatic and anti-inflammatory drug (Ardosons) as corrosion inhibitor for API 5L X65 steel in 1M HCl aqueous solution

X65 steel is a very important material for the oil and gas industry, particularly for the construction of transportation and storage infrastructure, this is due to the excellent electromechanical properties of the alloy and relative low cost of acquisition. However, it is prone to corrosion in acid media, HCl for example, which is used during cleaning and maintenance. Expired drug Ardosons was studied as a potential corrosion inhibitor for X65 steel in acid media (1M HCl) at different temperatures (25 and 40 ºC). Open Circuit Potential (OCP) displacement towards more noble values, indicates the formation of a protective adsorbed layer on the metal surface, the magnitude of this shift allows the classification of Ardosons as a mixed corrosion inhibitor. Electrochemical evaluation was carried out by means of Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization Curves (PDP), the maximum observed efficiency at room temperature is 77.1% according to EIS and 60.3% according to PDP, while at 40 ºC, it is 51.6% according to EIS. A thermodynamic analysis reveals that the adsorption mechanism follows the Langmuir adsorption isotherm with a free Gibbs adsorption energy (ΔG°ads) of −19.06 kJ⸳mol−1 at room temperature and −8.50 kJ⸳mol−1 at 40 °C, both adsorption processes correspond to physisorption.