low alloyed plain carbon steel for the manufacture of conduits for exploration and production of oil and / or natural gas with optimized corrosion resistance, process for manufacturing seamless pipes and processed seamless pipes.

摘要

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 CO2, 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,