Film-forming amines for corrosion protection of carbon steels in PWR secondary circuit conditions

International audienceDuring shutdown periods of pressurized water reactors (PWR), corrosion phenomena can affect some components of the secondary circuit. The use of environmentally friendly corrosion inhibitors such as film-forming amines (FFA) is an interesting way to attenuate or stop the corrosion of carbon steels, which constitute the major part of the circuit.The aim of the present work is to investigate the behavior and the efficiency of a FFA for the carbon steels protection under various physical and chemical conditions, close to those representative of the PWR secondary circuits. First, treatments with FFA were performed in laboratory conditions. A carbon steel rod of 1 cm2 cross-sectional area was used as rotating disk working electrode (RDE). The test solution was 10-3 M Na2SO4 diluted in deionized water. The pH was adjusted with ammonia and a heating bath was used to control the electrolyte temperature between 25 DC and 80 DC.Then, complementary treatments were carried out in an autoclave at temperatures between 100 DC to 275 DC. Hydrazine was added to ensure a complete consumption of dissolved oxygen (reducing conditions). The pH was adjusted with ammonia and ethanolamine. FFA were deposited on both carbon steel and oxidized samples to investigate the influence of the magnetite layer.The adsorption of the FFA and the efficiency of the films formed were characterized by electrochemical impedance spectroscopy (EIS).The influence of different parameters on FFA deposition such as temperature, FFA concentration, pH and rotation rate of the RDE was studied by EIS. In all cases, the impedance diagrams were characteristic of the formation of an organic thin film on the electrode surface. A positive effect of higher temperatures was observed in agreement with literature [1]. The effect of FFA concentration was attributed to a surfactant-type behavior with a critical concentration below which no efficiency was observed and a maximum efficiency (plateau) at high concentration. The influence of pH was linked to the oxyhydroxyde formation on the carbon steel surface as well as the chemical form of the FFA in solution (protonated or not). Eventually, the rotation rate, and by extension the hydrodynamics, seems to have little influence on EIS results during the film deposition and after the film formation. The electrochemical results were supplemented by surface observations with X-Ray photoelectron spectroscopy (XPS) analysis and contact angle measurements. [1] A study of anti-corrosion behavior of octadecylamine-treated iron samples. H-H. Ge et al. Appl. Surf. Sci. 156 (2000) 39-46