THE EFFECT OF DEPOSITS OF MINERAL SALTS AND CORROSION PRODUCTS ON THE METAL SURFACE ON THE EFFECTIVENESS OF INHIBITORY PROTECTION

The article presents the results of assessing the effect of deposits of solid mineral salts and corrosion products on the metal surface on the rate of corrosion and the effectiveness of inhibitory protection. A method of applying mineral deposits to the surface of metal coupons made of low-carbon steel is proposed in order to simulate the formation of deposits in field conditions. This method is based on holding a steel sample in a laboratory autoclave in a test solution saturated with a corrosive agent CO2 at a partial pressure of 3 MPa at a temperature of 60 °C for 168 hours. Corrosion studies were carried out in an environment containing CO2 (medium 1) and in an environment additionally containing O2 with a higher concentration of CO2 and CB compared to medium 1 (medium 2). The work shows that deposits on the steel surface affect the course of corrosion processes, increasing the rate of corrosion in medium 1 by 33.7 % from 0.51 to 0.77 mm/year, while the presence of small ulcers and pitting is noted, which subsequently affect the development of local corrosion defects. The corrosion rate of steel samples in medium 2 with deposits increased by 25 % from 0.78 to 1.04 mm/year, while the presence of small ulcers and pitting was also noted, which subsequently influenced the development of local corrosion defects. The use of corrosion inhibitors reduces the corrosion rate of steel samples without deposits by 97 % and with deposits by 78 %. It has been established that the effectiveness of inhibitory protection decreases in the conditions of formed deposits. It is concluded that none of the studied corrosion inhibitors can achieve the required corrosion rate of 0.1 mm/year.