Environmental Engineering Reference
In-Depth Information
Table 7.5
Results of ultrasound inspection of DN800 pipeline of teh repeated
forced circulation circuit of the nuclear power plant given as the ratio of the
number of identified discontinuities to the number of tested welds
Field welds Shop welds
circumferential circumferential longitudinal
1 2 3 1 2 3 1 2 3
1989 19 0 0 35 2 0.057 114 6 0.053
1990 24 3 0.125 20 5 0.25 96 10 0.104
1991 17 0 0 23 7 0.212 99 4 0.04
1992 43 2 0.047 38 3 0.079 112 3 0.027
1993 35 0 0 - - - - - -
1994 16 0 0 - - - - - -
1995 25 2 0.08 36 1 0.028 100 - 0.01
Total 179 7 0.08 162 18 0.11 251 24 0.046
Note. 1. Inspected number of welds. 2. Number of defective welds. 3. Ratio of the number
of defective welds to the number of inspected welds.
Year of
inspection
1995 - 179 welds inspected (31 field, 38 shop, no longitudinal). Defects
were not detected.
A total 902 welds were inspected (214 field, 193 shop, 533 longitudinal),
in addition, 191 intersection areas of the longitudinal joints with a
circumferential weld.
For comparison, Tables 7.4 and 7.5 show the results of inspection of
the DN800 pipelines for blocks 1 and 2 of the same nuclear power plant,
for which more extensive inspection was not performed before the start of
operation.
7.4.9 Optimum combination of inspection methods
The results of the probabilistic strength analysis of structural elements,
carried out to ensure correct organisation of NDT during operation can be
used to develop recommendations for optimum combinations of various
physical methods of NDT, NDT methods with other inspection methods,
including inspection of the parameters of operational loading of the
structure, NDT and hydraulic tests, NDT and inspection of leaks within
the LBB concept. Unfortunately, this line of work has not been sufficiently
developed, but some aspects of the problem and expected results can be
discussed.
ISI and inspection of the parameters of operational impact
In the case of superinspection at the stage of input inspection and the
initial stage of operation and the reduction of the probability of existence
in the structure of technological defects to an acceptable required level,
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