High temperature exposures were carried out to simulate long-time service. Rupture curves for exposed Grade 11 and Grade 22 steels did not exhibit the instabilities characteristic of the unused materials so that straight-line extrapolation gave good predictions of long-time strengths. Possibly due to a C-type reaction, strength predictions were poorer for Type 304 steel. Similar strengths were obtained using parameter tests of the unused materials. At the present stage of development, simulated service exposures offer an alternative, but not a superior, technique for extrapolating rupture characteristics.

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