Environmental Engineering Reference
In-Depth Information
probabilistic part of the residual defectiveness of the pipeline. The results
of the calculations carried out using the equation:
a
max
≥=
∫
P a a
(*
)
N a da
() .
def
res
a
in the graphical form are presented in Fig. 5.48 in the form of curve 1:
a
max
≥=
∫
The growth of the cracks with the size in the range 17 mm <
a
< 34 mm
in 1500 load cycles was determined by the standard procedure M-02-91
using the equation:
P a a
(*
)
N a da
() .
def
res
a
da
/
dN
c
= 5.80 · 10
-11
D
k
2.6
(1-
R
)
-1.3
,
Here D
k
is the range of the stress intensity factor;
R
is the stress ratio of
loading of the component.
The probabilistic part of residual defectiveness at the end of service,
determined taking into account the growth of the crack, is shown by curve
2 in Fig. 5.48.
Analysis of the position of the curves 1 and 2 in Fig. 5.48 shows
that the probability of existence of a continuous defect in the pipeline
prior to the start of the service is 0.01 and at the end of the service it is
0.03. Consequently, the statistical estimate of the probability of failure-
free operation on the basis of the leak criterion for a period of 20 years
in service is
P
(
t
) =
M
p
/
M
= 1 - 0.03 = 0.97. This means that out of 100
pipelines in service three pipelines will fail (leak). One of the pipelines
shows leaks at the very start of service.
5.3.3 Quantitative relationship of the dependability
indicators, determined by the criteria of fracture,
leakage or defect detection in service with the
NDT results
The method for determining the basic characteristics of reliability is described
below:
• reliability;
• failure rate λ(
t
);
• the number of failed structural elements according to the criteria of
fracture, leaks or defects;
• density function
f
(
t
) of time to failure during service time
t
.
The reliability of the product is one of the characteristics of its reliability.
The probability of failure-free service in the probability that the products will
Search WWH ::
Custom Search