The experience from using stretched flexible anodes in the system of electrochemical corrosion protection of main gas pipelines

Abstract

OOO Gazprom Transgas Yekaterinburg has had a positive experience in the use of stretched flexible anodes (SFAs) at linear sections of the gas main pipelines (LS GMPs) that are subjected to the effects of roaming currents. Their application has allowed the solution of a number of organizational and engineer ing problems related to providing the normative level of protection of LS GMPs.Organizational problems include difficulties (which are often unsolvable) that are related to the allot ment of land for mounting auxiliary corrosion protection facilities (CPFs) that are intended for the elim ination of alternating sign zones or zones of underprotection. Since stretched anodes are laid in the con servation zone of an operating GMP, the land that is allotted for such activities is in temporary possession. The provision of a normative level of protection for linear sections of GMPs in marshland is among the engineering problems that are solved using flexible anodes. One specific feature of marshes in the Urals is that they are shallow water reservoirs (2-7 m deep) that cover large areas on the surface of ledge rock. Tra ditional concentrated anodes (deep seated and near surface anode grounds (DAGs)) are not efficient due to their high spreading resistance and small protection arms. Mounting of distributed anodes requires sup ports (which are absent, as these pipelines run across a marsh) and official registration of a permanent land allotment for their placement. The application of a stretched flexible anode and its mounting in the winter solves these problems.All activities for the optimization of electrochemical protection (ECP) systems using flexible anodes were accomplished at OOO Gazprom Transgas Yekaterinburg in active gas pipelines that have operated for a long period of time. In addition to the task of providing the normative level of protection for the linear section of GMPs, it was necessary to solve the problem of the long term efficiency of a stretched flexible anode, i.e., to ensure its rated current density over the entire length. Attempts to evaluate rated current densities using calculations are senseless for an active gas pipeline with its nonuniform quality of insula tion, combinations of different types of ground, roaming currents, etc. Thus, the emphasis was placed on the methodological and experimental components of this work.Portable easy to mount module probes with work specimens from SFAs placed directly in the vicinity of an active SFA were developed and fabricated. Because they were connected to an anode, they allowed one to record the density of its current and its potential (see Fig. 1) [1][2][3][4][5][6]. A galvanodynamic curve was taken from them using a potentiostat, either under laboratory conditions or directly on the route. Based on this curve shape, the possible limiting current density was evaluated; above this density the process of water decomposition occurs, accompanied by the release of atomic oxygen on the anode surface, which is harmful to the elastomeric component of the SFA....