Allowable Number of Cycles due to German AD

Allowable Number of Cycles due to German AD-Regelwerk Reihe S
Requests for Calculations
Robert Kauer und Christian Hüttner
TÜV Süddeutschland Bau und Betrieb GmbH
Geschäftsbereich Energie und Technologie;
BU Risiko und Zuverlässigkeit
80686 München, Germany
[email protected]
INTRODUCTION
Globalisation and deregulation are main subjects to characterize the development
on the world market. Both changes yield to an increase in competition and in the end
the companies capability for innovation is responsible to remain. The goal of these
innovations always is to increase product quality with a minimum of costs.
Therefore an optimated operating management includes suitable measures to ensure present or to increase further availability of technical systems. For the considered systems or components the importance concerning availability have to be determined using probabilistic ridc assessment (PRA) [1]. On PRA-results not only the
expenditure for licensing calculations should depend but also the magnitude of inservice inspections [2]. Prior condition to optimize these measures is to perform
strength analyses of the considered systems.
To ensure sufficient dimensions using traditional codes and standards is not the
goal-directed way. With the introduction of German AD-Merkblätter Reihe S [3] (see
also ASME Sect. VIII, div. 2 [4]) methods are available, which are suitable not only
for the documentation of required specifications but also for the optimization of lifecycle costs (LCC).
FAILURE MODES
All kinds of analyses should be performed to avoid failures of critical components
concerning availability or safety. The knowledge of relevant failure modes is the basis for the determination of decisive loading conditions. In [3] forced rupture, inadmissible deformations, ratchting and fatigue are considered.
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LOADING
In [3] working loads are clssified into operating loads (BF), testing loads (PF),
mounting loads (MF) and special loads (SF). The classification allows suitable evaluation of the stresses and deformations due to these loads.
EVALUATION
Elastic-plastic evaluation methods [3] are based on the ASME-Code [4] where the
stresses are separated into stress categories (primary, secondary and peak stresses).
Under the prediction of quasi-static or cyclic loadings with low transients a linear
elastic analysis is sufficient to investigate the behaviour of the component concerning
the considered failure modes.
If there are rapid changing lodas, e. g. thermoshock, transient calculations have to
be performed.
The allowable number of cacles can be determined using fatigue curves. If there
are over elastic deformations correction factors can be used to transform the elastic
results.
Due to an increase in simulation expenditure (non-linear instead of linear analyses) more detailed realistic informations can be obtained [5].
The increase of strain increments due to high temperature effects can be included
by introducing creep laws. Instability and contact has to be considered by switching
to non-linear geometry conditions.
SUMMARY
With the intoduction of German AD-Merkblätter Reihe S methods are available not
only for the documentation of required specifications but also for the optimization of
life-cycle costs (LCC).
Concerning the depth in calculation there are various methods available, which
should be used in dependence on the importance of the considered components.
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REFERENCES
[1]
[2]
[3]
[4]
[5]
Sacher, H., Rauh, H.-J.: Ganzheitliche Vorgehensweise bei der Optimierung der
Betriebsführung. Neue Entwicklungen im Anlagenmanagement, Mannheim
17./18.11.1998.
Hüttner, Ch., Binder, F., Holzer, W.: Mit Beanspruchungsanalysen und Monitoring Prüfkonzepte optimieren. Neue Entwicklungen im Anlagenmanagement,
Mannheim 17./18.11.1998.
AD-Merkblätter Reihe S. Beuth-Verlag.
ASME- Boiler and Pressure Vessel Code, Section III and Section VIII, Div. 2.
Kauer, R., Hüttner, Ch.: Gegenüberstellung von Bewertungskonzepten zur Auslegung, Berechnung und Konstruktion anlagentechnischer Komponenten.
MARC User Meeting, 27-29.10.1999.