Corrosion-Mechanical Failure of Pipe Steels in Hydrogen Sulfide Environments

The relationship between the hydrogenating of steels 20, 30CrMo and 17Mn1Si and their resistance to corrosion-fatigue fracture under static and cyclic loads in NACE solution has been investigated. It was found that the volume of adsorbed hydrogen does not determine the corrosion cracking resistance of steels. Steels 20 and 17Mn1Si absorb about the same amount of hydrogen under static loads, however their corrosion cracking resistance is different. The threshold tension for 20 steel is less than for 17Mn1Si steel. Corrosion fatigue resistance of 20 steel under cyclic loads is higher than of 17Mn1Si. Absorption of hydrogen by steels increases under the action of tensile static stresses and decreases at the symmetric cyclic loading. The threshold tension for 30CrMo steel at static stresses is high enough (440 MPa, σ_th/σ_0.2 = 0.8), but threshold average tension does not reach at cyclic asymmetric stresses with amplitudes σ_a = 0.2σ_0.2 and samples fail before 720 h. It indicates a higher sensitivity of this steel to the action of cyclic asymmetric stresses compared to 20 and 17Mn1Si steel. Reducing of resistance to corrosion-fatigue fracture of 30CrMo steel under asymmetric cyclic loads correlates with the change in the hydrogenating nature of environment. Corrosion-mechanical failure of steel 20 occurs mainly as a result of hydrogen embrittlement, and the failure of steel 17Mn1Si caused by the simultaneous action of corrosion and hydrogen factors.