Dynamic and Static Crack Propagation Proparties of Austenitic Steels in Dilute Acidic Geothermal Brine

Austenitic steels for geothermal power plants may meet with failure by stress corrosion in geothermal brines containing Cl−. In this concern, dynamic and static crack propagation properties were investigated for austenitic steels (SUS304 and SUS316) in dilute acidic geothermal brine at Onikobe containing 5400 ppm of Cl−. Experiments were made with apparatuses installed at Onikobe, and results obtained were analyzed especially referring to fractographs.Results were summarized as follows:(1) Dynamic crack propagation of austenitic steels except sensitized SUS304 appeared to be that of corrosion fatigue, for the rate of crack propagation depended on the frequency.(2) As for dynamic crack propagation of sensitized SUS304, the rate of crack propagation increased rapidly in the region of ΔKI≥15 MPa·m1⁄2 at a low frequency (0.002 Hz) by predominant influence of IGSCC.(3) For sensitized SUS304, KISCC was presumed to be about 19 MPa·m1⁄2, and KFSCC (the value of ΔKI at which the influence of SCC begins to appear in dynamic crack propagation) was presumed to be about 15 MPa·m1⁄2.(4) For SUS316, no characteristics of IGSCC were observed even in sensitized specimens.