Environmental Engineering Reference
In-Depth Information
Another experiment involved ten NDT inspectors (Fig. 5.19). The
analyzed the test sample (DN800) contained four types of defects (lack
of penetration, incomplete fusion, slag, pores). The NDT inspectors were
ranked based on the results of inspection of one type of defect (the best was
assigned '1', the worst '10'). It turned out that the nature of the ranking
does not depend on the type of inspected defect. The best NDT inspector
shows the best results for all types of defects. The worst case shows
the corresponding results also for all kinds of defects. Thus, the 'human
factor' in flaw inspection in this experiment was stable and a major factor
influencing the quality of inspection.
To conclude this section it can be noted that the described inspection
results obtained in assessing the detectability of NDIS, used in nuclear
power plants, indicates the great importance of these studies for predicting
and ensuring the required service life, reliability and safe operation of
pressure vessels and piping of nuclear power reactors. The next section
presents the main results obtained in the framework of PISC, which provide
a more comprehensive view of this important issue.
5.1.5 Results obtained in the PISC programme
The research program to investigate the reliability of structural elements
working under pressure in nuclear power plants of American manufacture
(Programme for the Inspection of Steel Components, PISC) was initiated
by the Commission on the strength of reactor casing (USA) and was carried
out during 20 years in the Commission of the European Community (CEC)
and the OSCE with the participation of 18 countries. The programme was
implemented in three phases. After completion of the PISC-I programme, the
PISC-II programme was developed and implemented, and this was followed
by the PISC-III programme. The results of these studies are presented in
accordance with the publications Ref. 76-83.
The aim of the PISC-I programme was to study the reliability of
determination of the linear dimensions of the defects by ultrasonic testing,
recommended for NDIS of equipment of nuclear power plants by the
ASME (XI) rules. The technique is based on 50% DAC calibration and is
recommended for manual ultrasonic testing of welds and the heat-affected
zone of the reactor vessels from the outside.
Two plates and one plate with a pipe branch with diameter of 18 inches
with artificial defects (Fig. 5.20) were proposed for inspection. All defects
were introduced during welding, and after ultrasonic testing they were cut
at the Research Centre of the CEC in Ispra (Italy). Several test samples
were also transferred for further investigation by the defect opening method
at IPA (Stuttgart) and other organisations (a total of six organisations).
The results of non-destructive and destructive testing were processed in
order to obtain the following results:
• probability of detection (POD);
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