Re: Pitch and catch, Tip diffraction

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Re: Pitch and catch, Tip diffraction
Posted by: Udo Schlengermann (PID_172), E-mail: uschlengermann@krautkramer.de, on March 16, 2000 at 08:58 :
In Reply to: Pitch and catch, Tip diffraction posted by : Jacques Parent on March 15, 2000 at 15:03:
reply by Udo Schlengermann:
It is not necessary to use mode conversion (pitch and catch) from transverse to longitudinal wave.
Simply use a broad band normal beam probe, at least 5 MHz, 10 MHz would be better, on the outer surface and increase the gain to get a diffracted signal from the crack tip together with the backwall echo (inner surface echo).
If the instrument is calibrated on a stepped block and by knowing the wall thickness, the time of flight difference of the two signals shows the depth of the crack at the given position of the probe.
The only problems are to resolve the two signals (low diffraction signal, high backwall echo against each other and against noise level.
But if the crack is some millimeter deep I see no problems with tube steel.
You can move the probe to follow the crack.
Kind regards
Udo Schlengermann
------------
: I have an application where I need to confirm and size a longitudinal crack, ID initiated, on a 12.75" OD pipe, wall thickness 2.343".
: The crack is running between tube holes which are separated by by ~3" of steel.
: We are thinking of a pitch and catch arrangement.
: We will "pitch" a shear wave, of appropriate angle, in the circumferential direction, to excite the bottom opening of the crack on the ID. (1/2", 2.25 MHz)
: We are hoping to "catch" the Tip Diffracted signal, with a normal beam probe, positioned directly above the crack location. By using Time of Flight in the absolute mode, we are hoping to measure the ligament above the crack tip and therefore the crack size (depth).
: 1) Any comments?
: 2) Any experience with something similar?
: 3) Any suggestions on the shear and/or normal probes specifications?
: 4) Any other ideas?
: Thanks
: jp

Follow Ups:

Re: Pitch and catch, Tip diffraction Jacques Parent 14:20 3/16/2000 (2)

Re: Pitch and catch, Tip diffraction Udo Schlengermann 09:03 3/20/2000 (0)

Re: Pitch and catch, Tip diffraction J. Mark Davis 16:59 3/16/2000 (0)

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: reply by Udo Schlengermann: : It is not necessary to use mode conversion (pitch and catch) from transverse to longitudinal wave. : Simply use a broad band normal beam probe, at least 5 MHz, 10 MHz would be better, on the outer surface and increase the gain to get a diffracted signal from the crack tip together with the backwall echo (inner surface echo). : If the instrument is calibrated on a stepped block and by knowing the wall thickness, the time of flight difference of the two signals shows the depth of the crack at the given position of the probe. : The only problems are to resolve the two signals (low diffraction signal, high backwall echo against each other and against noise level. : But if the crack is some millimeter deep I see no problems with tube steel. : You can move the probe to follow the crack. : Kind regards : Udo Schlengermann : ------------ : : I have an application where I need to confirm and size a longitudinal crack, ID initiated, on a 12.75" OD pipe, wall thickness 2.343". : : The crack is running between tube holes which are separated by by ~3" of steel. : : We are thinking of a pitch and catch arrangement. : : We will "pitch" a shear wave, of appropriate angle, in the circumferential direction, to excite the bottom opening of the crack on the ID. (1/2", 2.25 MHz) : : We are hoping to "catch" the Tip Diffracted signal, with a normal beam probe, positioned directly above the crack location. By using Time of Flight in the absolute mode, we are hoping to measure the ligament above the crack tip and therefore the crack size (depth). : : 1) Any comments? : : 2) Any experience with something similar? : : 3) Any suggestions on the shear and/or normal probes specifications? : : 4) Any other ideas? : : Thanks : : jp

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