Re: UT of filled or unfilled pipes Dear Mr. Neubert,
the echo of a backwall or a reflector is influenced by the
media behind the backwall/reflector. In practice this effect
can normally be neglected.
In the case of a longitudinal wave in a steel pipe wall, the
reflection coefficient changes from nearly 1 (air filling) to
0.937 for the water filled pipe. That means, that the loss of
backwall amplitude due to the water filling is less than 0.6 dB.
This can be neglected compared with other effects to the signal
amplitude, e.g. changing coupling conditions.
In the case of shear waves, the amplitude loss due to water
filling might be slightly higher, but does not exceed 1 dB.
(The shear wave impedance is smaller then the long wave
Additional, water film or water drops can cause unwanted
echos. If there is a waterfilm on the backwall of a component,
the echo from the waterfilm surface may interfere with the
components backwall echo. But due to the fact, that only
12 percent of the sound energy penetrates the backwall,
this effect is also not significant.
The normally used UT-waves are only minor influenced by
the water filling. This also includes creeping waves and
long-shear wave conversion. Rayleigh waves are much more
influenced, through a high damping caused by the water and
through reflections caused by water drops.
The above mentioned facts are valid for steel pipes. If you
think about other materials, e.g. aluminum pipes with a
much lower acoustic impedance, the water filling will have
a higher influence!
: I got the task to find out if there`s a difference in
: mechanized UT of pipes under unfilled and filled
: conditions (by water) as a 1st measurement (basis) for
: the in-service inspection of Nuclear power plants.
: Who knows some literature and where were made such
: I hope You, the ndt.net users can help me.
: Thanks in advance.
: Joerg (e-mail please see above)
: phone: +49 9131 18 7895 fax: +49 9131 18 2053