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Technical Discussions
Rolf D.
Director, Editor
NDT.net, Germany, Joined Nov 1998, 602

Rolf D.

Director, Editor
NDT.net,
Germany,
Joined Nov 1998
602
06:14 Sep-26-1996
For what applications phased array probes could be preferable used?

Mr. Rathgeb described in his article that
one Phased Array Probe replaces several
standard probes. A Phased Array Probe generates different
angles of incidence by different delay times
between the array elements.

I assume that the described advantages could be very
usefully for other applications as well.

Do you know some of these possible domains?

Rolf D.



    
 
 
Rathgeb/Meier
Rathgeb/Meier
00:30 Sep-27-1996
Re: For what applications phased array probes could be preferable used?
: Mr. Rathgeb described in his article that
: one Phased Array Probe replaces several
: standard probes. A Phased Array Probe generates different
: angles of incidence by different delay times
: between the array elements.

: I assume that the described advantages could be very
: usefully for other applications as well.

: Do you know some of these possible domains?

: Rolf D.


There are some reasons for the use of phased arrays probes.
But first of all I want to point out, that the sound field
of a phased array probe with an electronical steered angle
is quite the same as of a single cristal probe with the
same "effective" cristal dimension. There is no "bad influence"
by the electronical steering. Additional to the ability to
select the beam angle, phased array probe allow the focusing
of the beam.

The use of phased array probes show advandages, if the code
requires the use of different angles. For example the ASME
code requires angles of 0 degrees, 45 degrees and 60 degrees.
All three angles can be covered by one probe.
Or the German KTA code requires for thick components the use of
a so called tandem-system searching for cracks oriented per-
pendicular to the surface. This could also be covered by a
phased array probe, using mode conversion techniques, where a
60 degree shear wave is transmitted which will be converted to
a compression wave at a crack surface. The compression wave is
than reflected at the backwall and will be recieved with the
same phased array probe, steered for this compression wave.

Phased arrays show also advandages at complex geometries, if
there would be an additional manipulator axis nesessary for
skewing. One can save this additional axis and skew electronically.
In this case the computation of the skew angle is not so
sensitive, because you can use a set of different skew angles.
You should only provide, that this set contains the right skew angle.
We also use phased arrayprobes with lateral skew, if there is
no given preverence for the crack orientation. Und last but not
least is the use of phased arrays whitch cover a wide angle area
very useful for evaluation and sizing using tomographic methods.

Our experience is, that in case of a 16-Element phased array probe
you can vary the angle of incidence bedween 0 to 80 degrees compression
wave, bedween 35 and 70 degrees shear wave and you can also produce
creeping waves. In case of skewing, the skew angle can vary bedween
nearly -45 degrees to +45 degrees. The angle can be steered in steps
of 1 degree and there is also the possibility for focusing.

Phased array probes are used for the inspection of reactor pressure
vessels and steam generators, for nozzle inspection, for the inspection
of stainless steel components with a distinct grain orientation and so
on.


Rainer Meier



    
 
 

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