Environmental Engineering Reference
In-Depth Information
Defect depth a , mm
5.44 Histogram of detected defects 1, initial defectiveness 2 and
residual defectiveness after repair of detected defects 3.
NA
P
N
=
c
− −η
n
,
in
[
]
= 1
(1
)exp
−α c−c −η
(
)
;
pdd
0
{
}
[
]
n
(
c = c
)
A
(1
−η
) exp
−α c−c −η
(
)
;
det
0
where A, n, α, η, χ 0 are constants.
The numerical values of the constants A, n, α, η are determined from the
condition of maximal approximation of equation N det (χ) to the NDT results
presented in the form of a histogram.
The minimum allowable defects size for detection χ 0 is determined in
setting flaw inspection equiment used for inspecting the product, or as the
minimum size of the defect which can be detected in inspection; in the first
approximation η can be taken as equal to 0. This leaves three unknowns,
which greatly simplifies the task of their definition.
The constants A, n , α can be determined either by solving a system of
three equations for A, n and α, which are obtained by taking three points
in the histogram, or the least squares method can be used.
Residual defectiveness N res is defined as the difference between N in and
N det :
￿ ￿ ￿ ￿ ￿
N res (χ) = N in (χ) - N det (χ).
Moreover, the number of defects remaining in the product after NDT
and repair is defined in three ranges.
The residual defectiveness N res.cr in the range of the defects that are
important for safety is determined as the number of defects in the product
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