Environmental Engineering Reference
In-Depth Information
5.1.2 Probabilistic relationships of inspection.
Detectability of inspection
Probabilistic relationships of defect detection have been studied
insufficiently. Even the PISC programme in which one of the principal
goals was to study the detectability of defects, could not cover all aspects
of the problem (despite the duration of studies for almost 15 years with
the participation of 16 Western countries including the USA and Japan). In
Russia, the pattern of detection of defects (including the probabilistic
aspects) was studied by A.K. Gurvich, V.G. Shcherbinsky, N.P. Aleshin and
others. In VNIIAES this problem has been studied since 1978
To understand the laws of probabilistic relationships of defect detection,
it is desirable to describe more accurately concepts such as detectability of
the control and the probability of detecting a defect.
The notion of detectability of inspection and related terms has
been analysed most extensively by V.N. Volchenko 75 . He uses the term
comparative detectability, understanding it as the objectivity of inspection,
i.e. degree of coincidence of signals relating to quality with the actual
values of its indicators. It is assumed that the real value of quality indicators
is assessed by a reference method. When inspecting by NDT methods, the
reference method can be metallographic examination of defects in layer
cutting of components (i.e. in fracturing components.)
The relative detectability can be quantified by the probability of making
error-free decisions when evaluating the quality of the object or a batch
of components. Thus, the quantitative characteristic of the reliability
of inspection is associated with the norms of defects in contrast to the
detection of defects. Detection of defects is the probability of detecting a
discontinuity on the basis of the specified parameter of the discontinuity.
An important indicator of the detectability of inspection is the repro-
ducibility of its results. This characteristic can be defined as the frequency
of coincidence of test results in different conditions. Reproducibility may
be a particular characteristic of detectability.
In terms of the strength nd lie the real reliability unlike the relative
detectability of inspection serves as the controlling characteristic of the
detectability of inspection. Real reliability of non-destructive inspection
can be defined as the degree of coincidence of the NDT results with the
real characteristics of discontinuities in the structure.
The opportunity to systematically investigate the real detectability of
NDT appeared after the development of manufacturing technology of test
specimens with artificial discontinuities to fully simulate the discontinuity
of technological and operational nature.
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