Creep-fatique properties of grade 91 steel

Rami Pohja, Asta Nurmela, Pekka Moilanen, Stefan Holmström

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review


The creep-fatigue properties of modified 9Cr-1Mo (grade 91) steel have been investigated for the purpose of design in cyclic service. In this paper test results from creep-fatigue (CF) and low cycle fatigue (LCF) on grade 91 steel are reported. The tests performed on the high precision pneumatic loading system (HIPS) are in the temperature range of 550-600ºC, total strain range of 0.7-0.9% and with hold periods in both tension and compression. Curves of cyclic softening and stress relaxation are presented. The CF test results and results obtained from literature are also analysed using methods described in the assessment and design codes of RCC-MRx, R5 and ASME NH as well as by the recently developed -model. It is shown that the number of cycles to failure for CF data can be accurately predicted by the simple -model. The practicality in using the life fraction rule for presenting the combined damage is discussed and recommendations for alternative approaches are made.
Original languageEnglish
Title of host publicationAdvances in Materials Technology for Fossil Power Plants
Subtitle of host publicationProceedings from the 7th International Conference, EPRI 2013
PublisherElectric Power Research Institute
Pages679 - 689
ISBN (Print)978-1-6270-8060-6
Publication statusPublished - 2013
MoE publication typeNot Eligible
Event7th International Conference on Advances in Materials Technology for Fossil Power Plants - Waikoloa, United States
Duration: 22 Oct 201325 Oct 2013
Conference number: 7


Conference7th International Conference on Advances in Materials Technology for Fossil Power Plants
Country/TerritoryUnited States


  • grade 91 steel
  • creep-fatigue
  • life fraction rule
  • modelling


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