A Limited Comparison of the Mechanical Strength of Austenitic Steel in 1200 F Sodium, Air, and Helium

The mechanical properties of 316 stainless steel were measured at room temperature and at 1200 F during exposure to environments of air, helium and “clean” sodium. The test results were: Test: Cyclic strain / Environment: Air - Least cycles to failure; Environment: Helium - Most cycles to failure; Environment: Sodium - Between air and helium values. Test: Rupture / Environment: Air/Helium - No significant difference in rupture strenth; Environment: Sodium - Possible increase in ductility compared to air. Test: Creep / Environment: Air - Lowest rate; Environment: Helium - Highest rate; Environment: Sodium - Between air and helium values. Test: Tensile / Environment: Air/Helium/Sodium - 5 percent or less difference in tensile strength; 6 percent or less difference in yield strength. The small changes seen in the rupture, creep, and tensile tests, due to different environments, are considered insignificant when compared to overall variations between heats of stainless steel. The differences seen in cyclic strain tests reflect changes in material surface condition produced by environment.