RD&D-Programme 2004 - SKB

discontinuities. The study shows a good correlation between indications obtained from NDT
and actual defect sizes. Furthermore, the results of the investigations are also useful in describing
defects obtained in EBW welds. Another conclusion of the investigation was that a more
detailed study should be conducted to determine the detection capability of the NDT methods.
There is also reason to further study the technology for digital radiography, in view of the fact
that research and development to date has mainly focused on ultrasonic testing.
Based on the above, a project was initiated in 2003 at BAM (Bundesanstalt für Materialforschung
und -prüfung) entitled “NDT Reliability”. The 3-year project is focusing on inspection
of welds made by means of both EBW and FSW. The programme is described in greater
detail under the heading “Programme” below.
Within digital radiography, a similar methodology will initially be used for testing of FSW
welds as that used for testing of EBW welds. However, a review will be made of possible
development needs within the project “NDT Reliability”, which also deals with other development
work on digital radiography.
Development efforts within ultrasonic testing have been aimed at developing methods for
inspection of FSW sealing welds. For development of the testing methodology, a new phased
array ultrasonic system was procured at the end of 2002. The system meets the requirements for
FSW testing with regard to frequency range and greatly simplified programming compared with
the previous system. It is easier to control and focus the sound beam with the new system.
In order to enable a suitable testing frequency to be specified in the ultrasonic testing of FSW
welds, the sound attenuation and propagation properties of the structure have been studied.
Similar tests have also been conducted on material from copper lids and cylinders. Testing
methods have been defined on the basis of heretofore known types of defects that can occur in
FSW welds in copper. Furthermore, theoretically possible defect formations have been posited
and testing methods have been devised to cover these hypothetical cases as well.
The testing methods are being progressively improved by evaluation of the indications obtained
and comparison with the results from destructive tests.
The methods that are currently being developed and evaluated are all based on phased array
ultrasonic technology and can be described in brief as follows:
• Testing of discontinuities with principal extent in the radial-tangential direction. This testing
is currently being done from the top side of the lid with a 5 MHz probe that focuses in the
middle of the weld, see Figure 6-22a.
• Testing of discontinuities with principal extent in the axial-tangential direction. Two methods
are currently being tried with testing from the outer surface:
– Method 1 focuses on the area 2–10 millimetres from the surface and is performed with
a 10 MHz array probe that is controlled so that it simulates a double crystal probe, see
Figure 6-22b.
– Method 2 focuses on the internal part of the weld and is performed with a 5 or 10 MHz
phased array probe that is focused centrally in the weld, see Figure 6-22c.
• Testing of discontinuities with principal extent in the radial-axial direction. Two configurations
are currently being tried with 5 MHz phased array probes:
– Most of the welding volume is examined by one probe on the outer surface and one on
the inside of the lid. The probes scan at a 45 degree incident angle with direct throughtransmission
and with reflection against any discontinuities, see Figure 6-22d.
– For the lower part of the weld, the inside of the pipe is used as a reflector for two phased
array probes on the outer surface. The location of the receiver is varied depending on
whether the discontinuities are to be detected by defect echo reflection or back-wall echo
reduction, see Figure 6-22e.
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