Conditions of Hydrogen-Induced Corrosion Occurrence of X65 Grade Line Pipe Steels in Sour Environments

Hydrogen-induced cracking (HIC) tests were performed on fourteen types of X65 line pipe steels in various environments in which the hydrogen sulfide (H2S) partial pressures (PH2S) were in the range from 1 × 10/5 MPa to 0.1 MPa and pH was in the range from 2 to 5. The conditions governing HIC occurrence were investigated and the following results were obtained: —Hydrogen permeability in steel ([PerFe]) was formulated as a function of PH2S and pH ([PerFe]) = 7.1 + 0.96 × (1.4logPH2S − 0.51 pH), where 0.1 MPa ≥ PH2S ≥ 1 × 10−3 MPa and 5 ≥ pH; [PerFe] = 3.3 + 0.75 × (0.3logPH2S − 0.51 pH), where 1 × 10−3 MPa > PH2S ≥ 1 × 10−5 MPa and 5 ≥ pH. —Critical hydrogen permeability in steel ([Percrit]) was expressed as a function of the critical length of inclusions (acrit) and the maximum hardness of the center-segregation zone (Hvmax) for the investigated thermomechanical-controlled process (TMCP) steels and the controlled rolled and air-cooled (CR) steels (log [Percrit] = [1.7 − 0.0030 Hv] − 1/4log[acrit])...