06:42 Jun-03-1997 Rainer Meier R & D retired from intelligeNDT Systems & Services, Germany, Joined Nov 1998 15
Re: dual phased-array probe : To: Mr Mohr
: For the inspection of dissimilar weld, you are using a dual phased-array probe. What are the advantages of a dual phased-array probe rather than a conventionnal phased-array probe. Does it eliminate the wedge echoes, the secondary lobes...
: Thank you
: Andre Lamarre, RD TECH
Since Mr. Mohr is not present, let me give the answer to your question.
The dual phased array probe described in Mr. Mohr's paper has been developed for the inspection of welds in stainless steel components with wall thickness between 20 and 80 mm. It fullfills the requirements of the EPRI Vessel Internals Programm (VIP), which demands an inspection with 45° shear wave and 60° long wave as well as the inspection of both surfaces. It is designed as a dual probe, to avoid wedge echos in the surface near zone.
Using the dual array, you will get a very small probe system, consisting of only one or two probes. The array probe is able to produce - 30° to 70° shear wave - 36° to 79° long wave - 0° long wave for wall thickness measurement and coupling ceck.
Therefore, using only one dual probe, - the probe near surface can be inspected with 70° long wave (searching for cracks) - the volume can be inspected with 45° shear wave and 60° long wave. The 45° shear wave covers the whole signal path from steel entrance till full skip. - searching for cracks at the probe far surface can be done with 45° shear wave (corner effect) - small cracks starting from the probe near surface can be sized using 70° long wave - deeper cracks or cracks starting from the backwall should be sized using 60° long wave - for sizing the array probe enables the use of not only one angle of incidence but a set of different angles. This im- proves the precision of the sizing result.