Environmental Engineering Reference
In-Depth Information
not fail in the given operating life (GOST 27.002-89).
Statistical evaluation of the probability of failure-free operation for time
t is determined from the relation:
P ( t ) = M p / M , [5.27]
where M p is the number of serviceable items at the end of time t ; M is the
number of items set for inspection or service.
As seen from the above expression, to estimate the probability of
failurer-free operation it is necessay to collect have a sufficient number of
products and test them or put into operation. 95
This approach has drawbacks because it requires a certain time and
material resources for testing or service with possible losses from unreliable
operation of the product. In addition, this approach is not applicable in the
case of unique expensive and/or highly dangerous products, for example,
the reactor vessel of modern nuclear power plant,.
In this regard, a special method of predicting reliability characteristics
was developed. 94
The method for determination of the reliability products includes the
definition of the probability of faultless operation of the product P ( t ) at time
t . To determine P ( t ), the reliability criteria for defects, leaks or failure are
determined before operation without prior testing or without prior use of
the product based on the results of non-destructive testing, the reliability
characteristics of the NDT method used and the growth rate of probable
defects during time t . To do this, the product is subjected to NDT and
the detected defects are repaired, and a histogram of the detected defects
in the coordinates 'characteristic defect size χ - number N det of detected
defects of the given size χ' is constructed. The quantitative characteristic
of the reliability of the NDT method used in the form of the probability of
detection of defects P dd (χ) is determined by the initial defectivness of the
product N in (χ) is calculated from the equation:
￿ ￿ ￿ ￿ ￿
N in (χ) = N det (χ) / P dd (χ). [5.28]
The initial defectiveness of the product is a combination of all the defects
in it before NDT; the initial defectiveness of a product can be defined in
different ways described in the invention 97 .
The residual defectiveness of the product N res (χ):
N res (χ) = N in (χ) - N det (χ). [5.29]
Residual defectiveness is the total set of defects undetected because of
imperfenctions of NDT and of the defects missed in NDT and sent to service
and remaining in the product after NDT and repair (removal) of identified
defects; more details can be found in Ref. 97..
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