Background According to statistical studies of the causes of failures and destruction of main gas pipelines, metal corrosion and the formation of its products are the main complications that significantly reduce the service life of this important type of oil and gas equipment. At present, it is impossible to conduct in-line diagnostics on more than 2,000 km of gas pipelines of Gazprom Transgaz Ufa LLC due to the lack of equal pass areas, inspection shells of small diameter and stationary cameras for receiving and launching diagnostic devices. The diagnostic methods used in these conditions (electrometric, magnetometric, shuggy examination) do not allow the development of underfilm corrosion to be detected, which often leads to erroneous conclusions about the corrosion situation in the gas pipeline section and its technical condition. Aims and Objectives The aim of the work was to assess the influence of various factors (size of corrosion damage, magnitude of cathode polarization current, depth of location of a corrosion defect, etc.) on hydrogen emission under a protective coating of a gas pipeline. In this case, the main task of the study was to determine the influence of the density of cathode current supplied to the protected gas pipeline and the corrosion rate of steel under insulation flowing with cathodic depolarization on the intensity of hydrogen emission above the ground in the area of the film corrosion. Methods Standard research methods were used: measuring the pH of model corrosive media imitating a ground electrolyte, as well as differences in electrode potentials in different parts of the metal surface under insulation. To determine the corrosion rate of specimens from St3, the bulk test method was used. An original method was also used, which made it possible to assess the presence of a corrosive process under the film by means of registering the hydrogen emission released during hydrogen depolarization. Results It is shown that the proposed method provides a fundamental possibility of registering the hydrogen emission over a corrosion defect. The influence of factors contributing to hydrogen depolarization under a protective coating on the emission intensity has been revealed. The test results allowed to calculate the maximum hydrogen concentration above the corrosion center.