Methods for the Improvement of Corrosion Resistance of Low-Alloy Steel Pipes for the Oil-And-Gas Extraction Industry

We develop a complex technology of fabrication of oil-and-gas pipes with elevated corrosion resistance, including the procedure of controlled forge-rolling of pipe blanks of 06X1-Y steel with regulated contents of chemical elements and the procedure of heat treatment, namely, hardening with double short-term high tempering at temperatures maximally close to the temperature of the α → γ phase transformation of steel. It is shown that pipes made of this steel have a fine-grained ferrite-pearlitic structure with high (up to 23%) contents of special α –α and α –γ low-energy boundaries and elevated corrosion resistance observed in the course of testing of the specimens in chloride and model chloride-acetate solutions. Moreover, these pipes are less susceptible to hydrogenation under the conditions of cathode polarization in 1 N H₂SO₄ + 1.5 g/liter CS(NH₂)₂ and exhibit higher resistances both to sulfide stress corrosion cracking (SSCC) and to hydrogen-induced cracking than the pipes made of 20 steel. It is shown that the procedure of heat treatment performed according to the developed technology increases the SSCC resistance (σ_gr ≥ 0.85 σ_0.2) and improves the mechanical properties of the pipes up to the strength grade X56 according to the standard of the American Petroleum Institute API 5L.