Investigation by the scanning electron microscopy of corrosion resistance of the near-seam zone and base material of gas pipeline pipes using comparative analysis method

The article provides a comparative analysis of the corrosion resistance of the base material and the near-seam zone of gas pipeline pipes made of low-alloy steel St3sp. The main attention is paid to the investigation of dif-ferences in the nature and intensity of corrosion damage in two key areas, such as the main pipe material and the NSZ, which is thermally exposed during welding. The results of the study confirm that corrosion poses a serious threat to the integrity and safety of oil and gas equipment, leading to significant economic losses and emergency risks. The research methodology includes visual inspection of samples operated under real conditions and microstructural analysis using scanning electron microscopy (SEM) with a secondary electron detector, which is optimal for studying surface morphology. The results of microstructural analysis revealed significant differences in the morphology of corrosion. NSZ is characterized by intense local corrosion in the form of deep ulcers framed by cluster-shaped loose corrosion products and radial microcracks, which indicates the development of corrosion in depth. In contrast, the base material is characterized by relatively uniform and slow corrosion with the formation of layered structures and linear microcracks without deep local damage. The main reason for the increased vulnerability of NSZ is structural changes in the metal (for example, the formation of martensite) and residual thermal stresses that occur during thermal exposure during welding. Welding is accompanied by local heating, which worsens the mechanical properties and corrosion resistance of the metal in this area. Based on the data obtained, a comprehensive approach to the protection of gas pipelines is proposed, focusing on the most vulnerable NSZ. Recommended measures include the use of insulating materials (heat-shrinkable couplings), protective protection with galvanic anodes, heat treatment of welded joints with induction currents to relieve stress, and purification of transported raw materials from aggressive impurities.