The method of strain range partitioning developed by Manson offers a possibility for treatment of creep-fatigue interactions. It partitions the strain-range of a complex hysteresis loop into four elementary strain range types. Although the method has its merits it is difficult to apply because of lacking experimental data and difficult loop reconstructions. The paper describes an approach which separates the inelastic strain range only into a fatigue portion and a creep portion following both a power law Coffin-Manson relationship. Coefficients and exponents were determined by a simple least square fitting procedure from a set of literature data. The plastic part agreed very well with the experimentally determined fatigue curve. The creep part could, however, only be understood using fatigue-modified stress rupture data accounting for cyclic softening. With this approach it was possible to determine number of cycles to creep failure as a function of the pure creep strain range. This procedure was applied to a set of literature data of grade 91 steel which covered a temperature range of 500°C, 550°C, 600°C with stress controlled and strain controlled hold-times. Life-times were predicted in a range corresponding with the scatter of pure fatigue or creep curves, which means that a very good agreement was obtained. The paper will give a thorough description of the procedure and demonstrate its applicability to design codes.

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