EFFICIENCY EVALUATION OF THE MONITORING PILOT COMPLEX FOR UNDERFILM CORROSION OF MAIN GAS PIPELINES

Abstract

Background The corrosion process under the influence of the soil electrolyte pipeline on the metal is accompanied by the release of hydrogen under the peeling insulation during cathodic depolarization. The volume of molecular hydrogen released due to the assimilation of electrons is proportional to this loss of metal mass. The upward flow of hydrogen due to the physical characteristics of this gas has a high penetrating ability with respect to the insulation materials and the structure of most soils and, as a result, without any difficulties moves over the center of pre-film corrosion through the soil, comes to its surface, where it can be registered with an appropriate detector both qualitatively and quantitatively. With this approach to monitoring under-film corrosion (UFC), there is no need to drill on the surveyed section of the pipeline. An analysis of the intensity of the hydrogen flow over the soil allows one to establish the location of the developing corrosion defect and assess the possibility of further operation of the pipeline without repair and restoration work. Aims and Objectives The aim of the work was to assess the possibility of determining the location of the PPC center by the recorded concentration of hydrogen over the soil surface without pitting. The following tasks were solved: to carry out test tests of the practical effectiveness of the developed method and the pilot complex for detecting hydrogen released during cathodic depolarization; establish the location of the corrosion center by the excess of hydrogen concentration over the background value. Methods A specially developed method for determining the concentration of hydrogen over the route of the main gas pipeline was used. This method and the pilot complex for its implementation make it possible to identify with high reliability the presence of a corrosion process on the surface of the gas pipeline by registering threshold values of hydrogen emission during cathodic depolarization on the metal surface under a layer of exfoliating protective coating and soil. Results Studies conducted with the help of the developed pilot complex of non-destructive testing of UFC confirmed the real possibility of reliable registration of the hydrogen flow on the soil surface above the axis of the gas pipeline. Using the software of this complex made it possible to establish the dependence of the hydrogen concentration on the surface on the duration of the measurements. It has been shown that over areas with a developing UFC center, the concentration of hydrogen exceeds the measured background value by more than an order of magnitude. The results of the control pit survey confirmed the presence of a corrosion lesion and the parameters of its localization on the pipe surface.