Design of ECP – electrochemical protection plants for underground utilitiesAny corrosion process leads to changes in properties of structural materials. It is obvious that economic losses, related to metal corrosion, are determined not so much by cost of corroded metal as by cost of repair works, losses due to temporary standstill in utilities, expenditures for prevention of accidents which are, in some cases, absolutely inadmissible in terms of ecological safety. In Saint-Petersburg and in Moscow, the cities with extensive dense network of underground utilities and developed electric transport, operation of steel pipelines is carried out in the most corrosive conditions. Estimate of costs related to corrosion shows that expenses for elimination of corrosion consequences are very considerable. A part of these expenses is inevitable. It is impossible to completely prevent all corrosion damages. Nevertheless, it is possible to significantly reduce corrosion losses due to practice of accumulated knowledge of corrosion processes and methods of protection from corrosion. The notion of "metal corrosion" includes a number of chemical processes causing fracture of metal. These processes sharply differ markedly from each other as per external manifestation, conditions and media in which they run, as well as properties of reacting metals and forming reaction products. However, there are reasons for their unification as all these processes have general result – fracture (oxidation) of metal.
Electrochemical protection of underground metal structuresThermodynamical instability of metals is cause of corrosion. Corrosion runs at interface of two phases «metal – environment» that is multistage process. Chemical and electrochemical corrosion is distinguished by a mechanism of metal oxidation process. Chemical corrosion is such processes of metal oxidation and corrosive agent regeneration, at which electrons are directly transferred to atoms or ions of oxidation (corrosive agent), which are mostly atmospheric oxygen. In heat supply the most widespread and practically important type of chemical corrosion is gas corrosion – corrosion of metals in dry gases (air, end products of fuel combustion) at high temperatures. Heat-resisting alloying of steels is applied, protection (regeneration) atmospheres are created, as well as thermodiffusion (on the basis of aluminum, silicon and chrome) and sprayed (on the basis of oxides of aluminum, magnesium, zirconium) protective coatings are used for protection against gas corrosion. Electrochemical corrosion is the most widespread type of corrosion and includes those cases when processes of metal oxidation and oxidation component regeneration run separately in medium of liquid electrolyte that is in current conducting medium. The following can be media: natural water, aqueous solutions of salt, acid, alkali, as well as air, soil and heat insulating structures, containing electrolyte (moisture) in a certain quantity. Summary data on corrosion processes running in operating pipelines of heat supply networks in the presence of moisture or its traces allows to confirm that all cases of rusting of pipelines and metal structures of heat supply networks occur as a result of electrochemical corrosion.
Protection methods against electrochemical corrosionProtection against electrochemical corrosion is a complex of measures aimed to prevention of corrosion processes, maintenance of equipment and facilities functioning within the required period of operation. Protection methods of metal structures against corrosion are based on purposeful impact resulting in complete or partial decrease of activity of factors enabling development of corrosion processes. Among the methods of impact to metal, protective and insulating coatings of continuous action (polymeric, glass-enamel, metal, zinc and aluminum) widely spread in the practice of protection of equipment and pipelines of heat supply organizations. Exposure to corrosive medium (water) is applied at protection against internal corrosion of tanks and vessels as well as pipelines by means of its inhibition or deaeration. Electrochemical protection allows to significantly decrease rate of corrosion processes on pipelines. At this type of protection electrochemical potential of a pipeline is shifted to the required (protective) area of potentials (structure charging) by means of its connection to the external power supply – cathodic protection station or galvanic protector. It should be pointed out that protection type for a certain facility shall be selected on the basis of analysis of its operation conditions. At that, the requirements to the values characterizing the required quality of facility operation, process features of the selected protection method and achievable economic effect shall be taken into account. Protection of underground utility steel pipelines against corrosion is an important task of the housing and utilities infrastructure of Saint-Petersburg, Moscow and other cities of Russia. Reliability and trouble-free operation of the life support system of social sector and industrial enterprises significantly depends on successful solution of this task.
The Engineering Infrastructure design Institute, LLC carries out all works on development of design documentation for protection of underground metal structures – from surveys related to corrosion to implementation of projects for protection installations (cathode, protector, drainage), including design of the operating remote control systems (ORC) of insulation damping for the heat supply networks.