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Behaviour of heat resistant power plant steels undergoing variable long term loading conditions
Author(s) -
Granacher J.,
Scholz A.,
Möhlig H.
Publication year - 2000
Publication title -
materialwissenschaft und werkstofftechnik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.285
H-Index - 38
eISSN - 1521-4052
pISSN - 0933-5137
DOI - 10.1002/(sici)1521-4052(200001)31:1<29::aid-mawe29>3.0.co;2-#
Subject(s) - term (time) , materials science , nuclear engineering , variable (mathematics) , metallurgy , environmental science , mechanics , mechanical engineering , engineering , mathematics , physics , mathematical analysis , quantum mechanics
High temperature components of power plants are in many cases subjected to variable loading conditions such as cyclic creep or strain cycling. Therefore the cyclic behaviour of important heat resistant steels has been investigated under stress control and to a smaller extent under strain control. The behaviour under cyclic creep rupture conditions was determined in long term experiments covering a wide range of loading conditions. This behaviour can be described with the modified life fraction rule and a factor concept of relative life for single stage cycles and additionally with a multi‐step hypothesis for multi‐stage cycles. The description can be adapted to estimate the life consumption under service type random conditions. The strain cycling behaviour was investigated in regard to the conditions of the heated surface of large components. To simulate this type of loading and to generate long term creep fatigue data, a service type strain cycle was developed. Anisothermal and comparable isothermal cycles were carried out up to 8000 h and delivered similar results. Long term isothermal tests on a bainitic and a martensitic turbine rotor steel could economically be performed up to 70 000 h by means of package type tests combining short term strain cycling and long term creep cycling. Creep fatigue life under single stage and multi‐stage conditions can be predicted on the basis of the generalized damage accumulation rule if an internal stress concept and preloading effects are considered. In the long term region governed by viscoelastic deformation, the creep fatigue behaviour can be approximated by the modified life fraction rule concept developed for cyclic creep. Cycle counter programs support the application of the life assessment concepts presented.