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In support of geothermal power plant development, Rockwell International's Energy Systems Group (ESG) has conducted extensive studies and tests on the behavior of materials in geothermal environments. The materials tested include both metallic and nonmetallic materials. This paper presents Rockwell's recent stress corrosion test data on structural steels and their weldments under uniaxial loading (stress, 80 percent of yield strength) in static Sinclair 4 geothermal brine at 204°C for 1700 h (10 weeks). The alloys tested were 26Cr-1Mo, 18Cr-2Mo, 9Cr-1Mo, and Type 316 stainless steel and their weldments. Under these test conditions, the following results were obtained: 1. In testing without air contamination: (a) Alloys 26Cr-1Mo, 18Cr-2Mo, and 9Cr-1Mo and their weldments were resistant to stress corrosion cracking; and (b) the average corrosion rates for the welded specimens made of 26Cr-1Mo, 18Cr-2Mo, and 9Cr-1Mo were 7.7 μm/year, 7.4 μm/year, and 18.2 μm/year, respectively. 2. In testing with air contamination: (a) the 18Cr-2Mo and 9Cr-1Mo ferritic steels were found to be resistant to stress corrosion cracking in air-contaminated brine; (b) Alloy 26Cr-1Mo and Type 316 stainless steel exhibited cracking typical of stress corrosion; and (c) the average corrosion rates were much higher than those obtained for the alloys without air contamination.
Results of the posttest mechanical properties testing and metallographic analysis are also presented.
fracture, stress corrosion, steels, geothermal brine, scaling
Member of the technical staff, Research and Technology Department, Rockwell International, Energy Systems Group, Canoga Park, Calif.
Manager, Research and Technology Department, Rockwell International, Energy Systems Group, Canoga Park, Calif.