ISO 20890-5-2020 pdf free.Guidelines for in-service inspectionsfor primary coolant circuit components of light water reactors — Eddy current testing of steamgenerator heating tubes.
During the eddy current testing of steam generator heating tubes, it is the task of the evaluation todifferentiate the recorded signals according to
– operational indications (location, expansion and possibly their type,e.g.cracks, abrasions, dents), geometric indications (e.g. of structural parts such as spacers,tube bottom, rolled-in slugs), and
other indications (e.g. of local fluctuations in the electrical conductivity and permeability, electricalinterference, wobble effect of the probes, impurities on the inside or outside of the tube, productionindications as well as any external parts present).
To attain a sufficiently accurate reproduction of the signal sequence, the spatial resolution shall be setso that the required spatial resolution is ensured by the selected sampling rate and the probe speed.The probe speed shall be dependent on the base frequency and sample rate and shall be no faster thanthe speed required to obtain a clear signal from the reference standard through-wall hole, within thecalibration limitations described in 6.3.3.2.
The following inspection technique can be used for the eddy current testing of steam generator heatingtubes as part of the standard technique:
Multiple frequency technique with internal bobbin probe (differential arrangement, see 4.3.1;absolute arrangement, see 4.3.3);
– Linking of the signals of multiple frequencies with internal bobbin probe in differentialarrangement(see 4.3.2).
lf the standard technique is inadequate for evaluation of the eddy current signals， eddy currenttechniques for more extensive evaluation (see 4.4 for additional techniques,e.g.rotating scanningprobes, matrix probes with T/R technique) or other non-destructive testing methods (e.g.ultrasonictesting, visual inspection) shall be applied.
Supplementary to the standard technique,eddy current techniques for more extensive analyses canalso be used as localisation systems in case of specific requirements (e.g. testing in the area of tubebottom/roll-in slugs).
The total tube circumference is recorded integrally when testing with an internal coaxial probe. Theextension of indication can therefore only be determined in the axial direction. In the undisturbedarea, evaluation of the signals of a frequency for determining location, depth and axial extension of anoperational change is sufficient.
lf indications overlap(e.g. operational indications and form indications), a statement is generally onlypossible with restrictions. The multifrequency technique shall then be used in the mix (linking ofmultiple frequencies) (see 4.3.2).
When testing operationally indications, the test frequencies used are generally in the range from10 kHz to 1 MHz. The basic frequency shall be selected so that the phase offset angle between a 20 %flat-bottom hole applied on the outside of a reference specimen and a through-wall drilled hole is in therange from 90° to 120°.ISO 20890 pdf download.