Melnyk M. Development of methods and devices for testing of underground pipelines' polarization potential

The thesis is devoted to solution of the topical and practically important scientific and technical problem of non-destructive inspection of complex protection against corrosion of underground metal structures. On the basis of the solution of the electrodynamics boundary problem, it is determined the dependences of effective capacitance of an insulated metal cylinder in electro-conductive medium on the electrophysical parameters of field's structure and frequency. It allows reasonable choosing the field's frequency for determination of the ohmic component of potential. It is shown that the solutions of the electrodynamics' problem with taking into account the dependence of the field distribution on frequency should be used for calculation of the capacitance of the metal construction with insulating cover in weakly conductive environment instead of formulae based on the equations for electrostatic field of a charged body. The method of determining the polarization potential of the metal surface in the electrolytic environment by measurement of direct and alternating voltages and harmonic factor determination for extraction of the ohmic component has been developed for control of the electrochemical protection against corrosion. It is found by comparison of the actual values of the transition resistance components for the underground pipelines (UP) that application of the proposed method of polarization potential determination for insulating cover's transition specific resistance <104 Om·m2 is rightful for AC voltage frequency in range of 2 ... 2000 Hz. It is created the VPP-M equipment with the coordinates determining module and the memory for contact measurements of direct and alternate electrical voltages which determines the polarization potential with the eliminated ohmic component and does not need deactivation of cathodic protection (CP) unit and using a compensator of voltage drop in an environment or stationary reference electrodes. The equipment VPP-M allows quickly to obtain a quantitative information about corrosion protection in different sections of UP and to detect the damaged insulation of UP by the known methods of Pearson and gradient. Combined utilization of VPP-M equipment together with BVC-K equipment makes it possible to determine the along-the-line distribution of both DC density of CP and the insulating cover's transition specific resistance in different sections of the UP. In case of DC protection it can be modulated by the signal with selected frequency or the AC generator can be applied. Metrological studies confirmed compliance the technical specifications of VPP-M equipment with standard requirements for UP inspection's equipment. It is found that the main relative error of potential measurements within four channels does not exceed 1.2%. Created VPP-M equipment was used in the field tests and experimental inspection on routes of underground pipelines. It was confirmed by the corresponding acts and the joint scientific publications.