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The study of cracks of X70 steel sample selected from the focal zone of destruction

The fuel and energy complex is the basis for the development of all sectors of the Russian economy. Its most important element is trunk pipeline system for the transport of gas, oil and their products. The main gas pipelines with cathodic protection, are exposed to the impact of ground electrolytes and tensile stresses. As a result, corrosion cracks may appear on the pipe surface. One of the most dangerous types of destruction of gas pipelines is stress-crack corrosion (SCC) of the outside cathode-protected metal surface of the pipes. There are no efficient methods for SCC control at present (the only method for SCC control is application of anti-corrosive insulation). One of the methods for detection of stress-crack corrosion is the stress test, however, its application is justified only for single cracks. There is a system of cracks in practice. Analysis of the focal zone of the collapsed gas pipeline with multiple cracks was carried out in this research. Studies were conducted on a sample of X70 steel made in Japan, selected from the focal zone of destruction of the West Siberia gas pipeline. The sample has 4 cracks typical for SCC crack. A metallographic analysis of the X70 steel and the calculation of the stress-strain condition of the metal were carried out. On the basis of the obtained results, it is proved that tested cracks have a corrosion-mechanical origin typical for stress-crack corrosion.