29. Influence of Static and Cyclic Tensions on Corrosion – Mechanical Destruction of Steels in Hydrogen Sulfide Environments

It has been investigated that influence, in terms of loading and composition of hydrogen sulfide environments, are resistant to corrosion-mechanical destruction of typical steels appointed to marine constructions, gas and oil equipment, and pipelines which are exploited on a marine shelf: steel 20, steels 10CrSiNiCu, 28Cr2МoVNbCu, 30CrМo, stainless steel 12Cr21Ni5Тi and steel of 17Mn1Si with the welded joint.

It is discovered that the high resistance of steels to sulphide stress corrosion cracking (SSCC) does not guarantee it high endurance in solution of NACE (5 % NaCl + 0.5 % CH₃COOH + H₂S, sat., рН3…4, t = 20 ± 3 °С) at cyclic tensions: at a symmetric cycle endurance the least resistant to SSCC of steel 20 goes down comparatively with air in ~1.4 times, and more resistant steel 30CrМo and 12Cr21Ni5Тi – in ~2.6 and 1.9 times, accordingly. An analogical tendency is observed at an asymmetric cycle at amplitude σ_а = 0.2σ_0.2. In presence of the welded joints asymmetric tensions reduce their resistance destruction in a greater measure, than specimen from basic metal. It has also been established that the addition of 3.5 % solution of marine salt 15 mg/l to H₂S does not influence the stress intensity factor of high-strength steel 28Cr2МoVNbCu. At the repeatedly static loading with frequency f = 1.1 · 10⁻⁵ Hz depending on the level of this steel strength, the value of conditional critical stress intensity factors K_scc in this solution goes down on 10–15 %.

Thus at the selection of materials for work in hydrogen sulfide environments, it is necessary, except for the generally accepted approaches, for an estimation of high ability to work to take the influence of alternating tensions.