Coatings are the most common form of corrosion protection for steel. The choice of a coating system depends on the corrosive environment in which it will be exposed and the required service life. A well-chosen protection system will reduce maintenance costs and provide corrosion protection over the intended construction lifetime. Coating systems that are expected to last for a long period of time in extremely corrosive environments often do not pass the appropriate tests prescribed by international standards because of their length and financial requirements. The assessment of coatings is carried out at the end of the period of exposure to accelerated corrosion tests in the chambers by visual means, that are prone to subjective evaluation, and adhesion measurements, which have high measurement uncertainty. The purpose of this paper was to improve the assessment of the durability by the use of electrochemical impedance spectroscopy (EIS), which enables continuous monitoring and quantification of coating quality through the impedance modulus. Different coating systems of known expected durability were tested in accordance with standard ISO 12944. For the first time, for the purpose of continuous monitoring of the impedance of the samples exposed in the chamber, an innovative setup with a cell in the form of two electrodes and a gel electrolyte was applied. For comparison, tests were also performed in a liquid electrolyte measuring cell made according to ISO 16773-2. Very small differences in the properties of high-quality coating systems whose impedance is > 10^10 Ω could be detected. Also, the loss of the protective properties of the coating was measured, which in poor coatings is characterized by a drop-in impedance below 10^6 Ω before the appearance of visual changes on the surface of the coating. The condition of the coatings before and after exposure in the chamber was also characterized FTIR, DSC, TGA analysis methods, surface tension and adhesion measurements, and correlation with the EIS method was analyzed. As a conclusion of the thesis, a new methodology for continuous monitoring of the coating impedance is proposed by using the assembly with flexible electrodes and gel electrolyte during exposure in chambers. The methodology presents a significant improvement, especially with high durability coatings, as it provides an impedance rating in the first 100 h of exposure before visually noticeable degradation, which can result in significant savings in test and subsequent maintenance costs.