Generation of creep-fatigue interaction diagram for modified 9Cr–1Mo steel. (June 2021)

• Record Type: Journal Article
• Authors: Veerababu, J.; Goyal, Sunil; Vanaja, J.; Nagesha, A.; Vasudevan, M.
• Is Part Of: International journal of pressure vessels and piping. Volume 191(2021)
• Publication Date: 2021-06
• Subjects: Creep-fatigue interaction -- Modified 9Cr–1Mo (Grade 91) steel -- Bilinear damage summation method -- CFI diagram; Pressure vessels -- Periodicals; Pipe -- Periodicals; Récipients sous pression -- Périodiques; Tuyaux -- Périodiques; Pipe; Pressure vessels; Periodicals; 681.76041
• DOI: 10.1016/j.ijpvp.2021.104376
• Languages: English
• ISSNs: 0308-0161

Abstract

Abstract: The selection of structural materials for elevated temperature applications relies on the availability of proper design codes based on adequate data pertaining to the properties at service-relevant loading conditions. Two of the most widely used high temperature design codes, viz, the ASME Boiler and Pressure Vessel Code and the RCC-MRx code are at variance with each other on the bilinear interaction point in the creep-fatigue interaction diagram for modified 9Cr–1Mo ferritic steel. In view of this, a detailed investigation was carried out on the creep-fatigue interaction behavior of this alloy with special emphasis on the evaluation of the creep-fatigue damage and construction of the interaction diagram. Tests were performed on two chemical variants of the steel at two temperatures (773 K and 823 K) using the strain amplitudes of ±0.25%, ±0.4%, ±0.6% and ±0.8%. Hold times of different durations in the range, 1–60 min, were imposed in the tensile and compressive peak strains to introduce the creep damage. The ASME creep-fatigue interaction diagram was observed to be a more conservative design approach for the alloy. Highlights: Modified 9Cr-1Mo steel exhibited continuous cyclic softening and compressive dwell sensitivity. Creep data was within the upper scatter band of 1.3 and 1.5 respectively compared to the RCC-MRx and the ASME creep data. A direct correlation was observed between the cyclic life and the magnitude of stress relaxation. The ASME CFI diagram was observed to be a more conservative design approach for Grade 91 steel.