The microstructure of the transmission gas pipeline part was studied. The part was discarded under the results of the magnetic inspection and visual control. Areas located near the outer surface of the tube on the transverse microsections were under consideration. The origin of the surface defects was defined. They were formed during the hot rolling of the sheet, which was used for the pipe manufacturing, they were not developed during the service time. A quantitative description of the main structural components, i. e. ferrite and pearlite, was conducted. The chemical composition of the prevailing non-metallic inclusions was determined and their morphology was described. Despite the presence of the large irregular shape particles, any secondary cracks formed during pipeline service were not detected in the part under consideration. Thus, the presence of the inner and surface defects did not cause any collapse of the transmission gas pipeline, possibly due to their morphological characteristics