ИСТИНА

The most widespread method of protection of underground constructions against corrosion is electrochemical protection (ECP) which effectively reduces metal corrosion speed. However, it is known that one of the most dangerous types of corrosion destruction – stress corrosion cracking (SCC) appears on underground pipelines at which the ECP works. It specifies that at cathodic potential local corrosion processes can proceed. As emergence of defects often is the first stage of corrosion cracking, the purpose of the real work was studying of processes of emergence and development of local (looks like pitting) defects at cathodic polarization and identification of the factors defining intensity of processes of defect formation. Observation of change of a surface of a working sample was carried out in borax buffer solution (pH6.7) with sodium chloride additives with use of "in situ" of optical microscopy, shooting the image of a surface with the video camera the Received images processed in the graphic editor. Electrochemical tests carried out by means of a potentiostat in a three-electrode cell. Simultaneous use of optical and electrochemical methods of research has allowed recording emergence of defects in the field of cathodic protection of underground constructions. The subsequent processing of images has allowed studying in detail kinetics of initial stages of local dissolution of steel at cathodic potentials. Influence of size of potential on emergence and development of defects has been investigated. With high precision are defined: the incubator period of appearance of defects, speed of filling of a surface of metal with defects, kinetics of development of individual defects on a surface. As potential shift to the area of negative values is followed by increase in speed of a hydrogen-charging of metal, investigated influence of penetration of electrolytic hydrogen into metal on processes of emergence of local defects for what added to working electrolyte a promoter of a hydrogen-charging thiurea, in parallel measuring the speed of penetration of hydrogen into steel. It is established that even at small concentration to 1 mm thiurea promotes an intensification of process of defect formation at cathodic potentials.