BS ISO 20890-5:2020 pdf download.Guidelines for in-service inspections for primary coolant circuit components of light water reactors Part 5: Eddy current testing of steam generator heating tubes.
During the eddy current testing of steam generator heating tubes , it is the task of the evaluation to differentiate 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 , electrical interference , wobble effect of the probes , impurities on the inside or outside of the tube , production ndications as well as any external parts present )
To attain a sufficiently accurate reproduction of the signal sequence , the spatial resolution shall be set so 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 the speed required to obtain a clear signal from the reference standard through-wall hole , within calibration limitations described in 6 . 3 , 3 . 2 .
The following inspection technique can be used for the eddy current testing of steam generator heating tubes 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 differential arrangement nses wma e mare wm y anm
for evaluation of the eddy current signals , eddy current ues , e or other non-destructive testing methods ( e.g. ultrasonic Supplementary to the standard technique , eddy current techniques for more extensive analyses also be used as localisation systems in case of specific requirements ( e.g. testing in the area of bottom / roll-in slugs )
4.3 Standard technique
4.3.1 Multiple frequency technique with internal bobbin probe in differential arrangement 4.3.1.1 Basic frequency
The total tube circumference is recorded integrally when testing with an internal coaxial probe . The extension of indication can therefore only be determined in the axial direction . In the undisturbed area , evaluation of the signals of a frequency for determining location , depth and axial extension of an operational change is sufficient .
If indications overlap ( e.g. operational indications and form indications ) , a statement is generally only possible with restrictions . The multifrequency technique shall then be used in the mix ( inking of ultiple frequencies ) ( see 4.3.2 ) .BS ISO 20890-5 pdf download.