Abstract
Design codes, such as RCC-MRx and ASME III NH, for
generation IV nuclear reactors use interaction diagram
based method for creep-fatigue assessment. In the
interaction diagram the fatigue damage is expressed as
the ratio of design cycles over the allowable amount of
cycles in service and the creep damage as the ratio of
time in service over the design life. With this approach
it is assumed that these quantities can be added linearly
to represent the combined creep-fatigue damage
accumulation. Failure is assumed to occur when the sum of
the damage reaches a specified value, usually unity or
less. The fatigue damage fraction should naturally be
unity when no creep damage is present and creep damage
should be unity when no fatigue damage is present.
However, strict fatigue limits and safety factors used
for creep rupture strengths as well as different
approaches to relaxation calculation can cause a
situation where creep-fatigue test data plotted according
to the design rules are three orders of magnitude away
from the interaction diagram unity line. Thus, utilizing
the interaction diagram methods for predicting the number
of creep-fatigue cycles may be inaccurate and from design
point of view these methods may be overly conservative.
In this paper the results of creep-fatigue tests carried
out for austenitic stainless steel 316 and heat resistant
ferritic-martensitic steel P91, which are included in the
design codes, such as RCC-MRx, are assessed using the
interaction diagram method with different levels of
criteria for the creep and fatigue fractions. The test
results are also compared against the predictions of a
recently developed simplified creep-fatigue model which
predicts the creep-fatigue damage as a function of strain
range, temperature and hold period duration with little
amount of fitting parameters. The F-model utilizes the
creep rupture strength and ultimate tensile strength
(UTS) of the material in question as base for the
creep-fatigue prediction. Furthermore, challenge of
acquiring representative creep damage fractions from the
dynamic material response, i.e. cyclic softening with P91
steel, for the interaction diagram based assessment is
discussed.
Original language | English |
---|---|
Title of host publication | Proceedings of the 22th International Conference on Nuclear Engineering, ICONE22 |
Subtitle of host publication | Plant Operations, Maintenance, Engineering, Modifications, Life Cycle and Balance of Plant; Nuclear Fuel and Materials; Plant Systems, Structures and Components; Codes, Standards, Licensing and Regulatory Issues |
Publisher | American Society of Mechanical Engineers (ASME) |
Number of pages | 10 |
Volume | 1 |
ISBN (Print) | 978-0-7918-4589-9 |
DOIs | |
Publication status | Published - 2014 |
MoE publication type | A4 Article in a conference publication |
Event | 22nd International Conference on Nuclear Engineering, ICONE 22 - Prague, Czech Republic Duration: 7 Jul 2014 → 11 Jul 2014 |
Conference
Conference | 22nd International Conference on Nuclear Engineering, ICONE 22 |
---|---|
Abbreviated title | ICONE22 |
Country/Territory | Czech Republic |
City | Prague |
Period | 7/07/14 → 11/07/14 |
Keywords
- creep-fatique
- modelling
- P91 steel