As per ISO376 : 2011, creep uncertainty can be measured directly or indirectly. In this regard, this paper seeks to provide a comparison between direct and indirect creeps computed from hysteresis. All computations for direct and indirect creeps were done using equations from ISO376 : 2011. Five force measuring devices were experimentally examined for this purpose. Results showed that the behaviors of direct and indirect creeps were quite different. The relative creep that was directly measured was constant. On the other hand, the relative creep that was indirectly estimated varied with the applying force. Therefore, the directly measured creep cannot be replaced by the indirect one. This paper proposes a method to use a representative value for indirect creep, as the maximum of the creep. For the force measuring devices that had good hysteresis characteristics, the directly and indirectly measured creeps were comparable. However, for the force measuring devices with poor hysteresis characteristics, the indirectly estimated creep was much higher than the directly measured creep. Therefore, it is highly recommended to measure the creep directly for the force measuring devices characterized by poor hysteresis.

This paper aims to verify the reliability of the creep-life assessment regarding the STS304H-Type tube for which the hardness method of H. Tanaka is used. For this purpose, the creep-rupture test and the hardness test were conducted with a new tube and used tubes that were exposed to 96,000 hr under a 650oC condition. The hardness value of the used tubes is higher than that of the new tube by approximately 12 Hv to 15 Hv. This test result was applied to the creep-life assessment of the STS304H-Type for which the H. Tanaka hardness method was used, and the life consumption of the used tubes was evaluated as 13%. The rupture times of the new and used tubes are 802 hr and 707 hr, respectively. The use of the test results as a substitution of the results of the Larson Miller Parameter for a life-assessment tool produced a life-consumption calculation of approximately 12%. Similar results can be confirmed between the Larson Miller Parameter method and the hardness method.