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- since 1996 -
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Technical Discussions
Carlos Correia
R & D, - -
UCV & EGROUP, Venezuela, Joined Oct 2008, 120

Carlos Correia

R & D, - -
UCV & EGROUP,
Venezuela,
Joined Oct 2008
120
14:03 Jun-17-2010
UT CREEPING WAVE IN LOW THICKNESS PIPING

Hello NDT brothers.
Which is the minimum thickness to perform a reliable creeping wave method inspection?
I need to evaluate ID connected cracks in Cr-Mo steel piping weld joints in a range from 7 to 10 mm.
I have used Creeping Wave before but not in this range.
Comments are deeply appreciated.

 
 Reply 
 
Luis Ganhao
Engineering,
USA, Joined Sep 2008, 25

Luis Ganhao

Engineering,
USA,
Joined Sep 2008
25
17:04 Jun-17-2010
Re: UT CREEPING WAVE IN LOW THICKNESS PIPING
In Reply to Carlos Correia at 14:03 Jun-17-2010 (Opening).

Carlos,

You can use creeping wave in that range of thickness, however you need a probe of 5Mhz and small size as well as a reference/calibration block which allow you to establish the properly range of inspection. I did this before in the same range and I could detect and estimate the size of some cracks. If you more questions please call me at +14036921037

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1286

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1286
23:13 Jun-17-2010
Re: UT CREEPING WAVE IN LOW THICKNESS PIPING
In Reply to Carlos Correia at 14:03 Jun-17-2010 (Opening).

zoom image

Carlos-7mm-30-70-70

zoom image

Carlos-7mm-70SW

Carlos; it may be possible to use the same principles as for thick wall but there will be problems to deal with. I did a quick CIVA model to illustrate. I used a 4MHz 8x9 element on a refracting wedge that provides 70° L mode in steel. You can see the 3 characteristic signals on the B-scan but the echo-dynmaic curve indicates that the one identified by some as the "creeping wave" occurs when the probe is almost directly over the flaw. This is the corner reflection from the bulk shear mode. Unless you remove the weld caps this will limit the usefulness of the 30-70-70 for sizing and detection.
A standard 70° transverse mode may provide an option if the tip of any surface-breaking flaws can be seen arriving earlier than the root geometry. I used the 8x9mm element again for the transverse wave probe but the element size could be made smaller to provide a smaller wedge so you can approach the weld cap closer with the exit point. For the transverse wave approach, the root geometry may provide a large signal that could make resolution of the corner and tip signals as separate from the root geometry difficult. But monitoring the region in time just prior to the root-geometry signal may be easier than trying to sort through the signals in the 30-70-70 probe.
 
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