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Title:
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Probabilistic FFP approach of a heat exchanger
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Author(s):
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Published by:
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Publication date:
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ECN
NUCNUC
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1996
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ECN report number:
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Document type:
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ECN-C--96-005
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ECN publication
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Number of pages:
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Full text:
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51
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Download PDF
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Abstract:
A probabilistic model for a DSM (Dutch chemical industry) heat exchangerE102 was developed and probability-based FFP (Fitness for Purpose) analyses
were compared with conventional deterministic FFP analyses based on PD 6493
(1991): Level 2. The probability of vessel failure at the mean working
pressure was calculated and uncertainty and sensitivity analyses were carried
out. Also the median failure load was predicted. A procedure to calibrate the
safety factors of a PD 6493 (1991) analysis was outlined and a strategy to
implement probabilistic UP models in the general FFP model was briefly
discussed. A great advantage of the probabilistic model was the power to
explore the uncertainty in the failure load. The model appeared to be very
helpful to find the type of distribution for the predicted failure load and
the cause of the uncertainty in the predicted failure load. The case study
showed that at the moment the use of probabilistic analysis models is
attractive and powerful to support the current deterministic defect
acceptance rules. It is possible to compute the probability of failure at the
maximum allowable load level according to a deterministic FFP analysis. First
and Second Order Reliability Methods (FORM/SORM) and the so-called hybrid
method, which is a combination of FORM and numerical integration are expected
to be able to predict the probability of failure rapidly and efficiently on
the present generation of PCs for most conditions. The use of these methods
enables the performance of sensitivity and uncertainty analysis quite easily.
Fracture of any welded steel structure with defects that break the surface or
are embedded can be analysed with a general probabilistic model based on a
suitable failure assessment code. 18 figs., 20 tabs., 23 refs., 1 appendix
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