Influence of Temperature and Velocity of Fluid on The Rate of Corrosion of Mild Steel in Existence of NPK (Nitrogen, Phosphorus, and Potassium) Inhibitor in Tap Water System

Abstract

The corrosion of using various concentrations of the NPK inhibitor on the mild steel in the tap water was investigated at various temperatures and 1.2 m/s fluid velocity. The results revealed that the efficiency of NPK inhibitors relies on the temperature and the concentration. The coverage ratio and efficiency increase due to the formation inhibitor’s layer on the metals’ surface; therefore, this stops the reaction of corrosion. The inhibitor’s efficiency decreases for NPK concentration above 75 ppm once the temperature increased above 35 ℃. The type of adsorption is followed the Frumkin model. The increase inactivate energy (Ea) at a low concentration of inhibitor maybe understand as the physical adsorption. The negative value of the change in enthalpy reveals the exo-thermic nature of the dissolution of mild steels. Furthermore, the negative value of (ΔS°) means increasing in disordering.