LOW-ALLOY CARBON STEEL FOR THE MANUFACTURE OF PIPES FOR EXPLORATION AND THE PRODUCTION OF OIL AND/OR GAS HAVING AN IMPROVED CORROSION RESISTANCE, A PROCESS FOR THE MANUFACTURE OF SEAMLESS PIPES, AND THE SEAMLESS PIPES OBTAINED THEREFROM

This invention relates to certain kinds of steel having a higher resistance to corrosion for their application in the manufacture of pipes used for oil and/or gas exploration and production in the petroleum industry. Particularly, the invention refers to a low-carbon steel having an improved resistance to corrosion, which is suitable for applications in the oil industry and particularly in environments containing CO . Low-alloy carbon steel for the manufacture of seamless pipes having improved resistance to corrosion, particularly the "sweet corrosion" that occurs in the media rich in CO, for using in exploration and production of oil and/or natural gas. The steel contains: 1.5-4.0% by weight of Cr, 0.06-0.10% by weight of C, 0.3-0.8% by weight of Mn, not more than 0.005% by weight of S, not more than 0.015% by weight of P, 0.20-0.35% by weight of Si, 0.25-0.35% by weight of Mo, 0.06-0.9% by weight of V, approximately 0.22% by weight of Cu, approximately 0.001% by weight of Nb, approximately 0.028% by weight of Ti, not more than a total value of O of 25 ppm, with the balance being Fe and unavoidable impurities. The process to manufacture seamless pipes comprises the stages of elaboration of a primary melt, followed by a secondary metallurgy stage with a strong desulfurization, addition of ferroalloys and chromium, and then the modification and flotation of the inclusions until the specified formulation is achieved; followed by casting, continuous hot-rolling, and optionally by normalizing, austenizing, quenching and tempering,