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andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
23:18 Dec-15-2010
Proof of creeping wave?

Proof of creeping wave?
Many years, too many years ago, I heard of ID creeping wave. I was hearing it from technicians who had been taught this method. My understanding of them trying to explain that the sound wave travels down a 31 deg. line hitting the opposite surface to mode convert into an L wave “creeping wave” was acceptable, but when they said if the sound wave hits an ID connected defect, the sound wave would then retrace its steps. (This implied that the sound wave had intelligence and knew where the probe was, so it could change direction.) This I put down to the technicians never understanding what he had been taught.
Time went past, and I attended a creeping wave course. The instructor professed to be THE EXPERT in creeping wave examination. But when I asked “How does the sound know when to reconvert to a 31 degree shear wave?” the answer was “…. it heads north at the first opportunity.” It was at this point, I knew there was some serious B/S being taught. I realized that this method is lowering the integrity of my profession. So whenever anyone asks about ID creeping wave, I tell them what I believe to be B/S. The laws of physics cannot be changed.
I was pleased to see Ginzel’s presentation on the None existence of creeping wave. It is clear from the video, the way the sound propagates. The NDT colleagues Hermann Wuestenberg and/or Anton Erhard from BAM, Berlin, Germany, and interpretation of their results may have been a mistake through lack of the technology available today.
The Ginzel auditory on the video, I don’t agree with 100 per cent but that is what a forum is for. The main part of the video is the fact it shows ID CREEPING WAVE is a myth. The perpetuation of this myth is, I believe, lowering the integrity of NDT.
If anyone has video evidence proof of the creeping wave. Please put it forward into the forum.

    
 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
21:08 Jan-07-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 23:18 Dec-15-2010 (Opening).

There was no one able to put forward video evidence of the so call “creeping wave”. I will put forward my opinion.
Transmitted Mechanical Energy
Transmitting sound through a solid is a mechanical process and will follow all the law of physics. There is no smoke and mirrors or anything other than simple acoustics. Anyone who says or preaches that sound breaks the laws of physics; either does not understand sound waves or trying to sell something that is contrary to the truth.
1 The piezoelectric transducer is excited by electricity from the plus generator.
2 The transducer deforms it shape rapidly at a frequency that is governed by the thickness and diameter, above the human hearing range. Thus being called ultrasonic.
3 The transducer is directly connected to a wedge.
4 If the transducer was pin head, the shock waves would be purely hemispherical radiating from its source.
5 In solids it is not possible to generate a primary wave mode without generating secondary and third wave modes.
6 Compression wave followed by a week shear wave, will radiate spherically from the source.
7 As the transducer has a significant dimension there are multiple points of contact and therefore multiple spherical shock waves radiating from the transducer at the same point in time. This is known as the Near Zone. The length is between 3 and 4 diameters independent of frequency.
8 As the spherical shock waves radiate away from the transducer, the part of the shockwave that is perpendicular to the transducer and a few degrease either side, will merge together into a singular wave front. This is known as the Far Zone.
9 This shock wave, wave front will grow as it propagates away from the transducer.
10 The wave front will hit the interface between the wedged probe shoe and the metal under test. At the interface, some of the energy will reflect off of the internal surface and bounce around inside of the wedge. A part of the energy will penetrate through this interface into metal. Due to the different times delay caused by the wedge, a new distorted Near Zone is created that is dependent on the frequency.
11 The wave front energy will refract and split into two direction as per Snell Law.
12 The wave fronts will keep growing as it radiates through the metal in three dimensions. If the growth of the wave front is drawn out on paper in two dimensions, it would be triangular. This is often called “Beam Spread.”
13 The formula for it half angle divergence is expressed as “sin theta 1.22 over wavelength over the diameter of the transmitting transducer.
14 The name “Beam Spread” is a misnomer and is confusing as the energy is a pulsed wave front.
14.1 The wave front if measured from the index point will have three angles.
14.2 The top line is known as the lead edge.
14.3 The bottom line is called the trailing edge
14.4 The centre line of maximum energy referred to as the angle of the transducer.
15 The centre line that is drawn is the mean average of the direction. It is not a beam of sound or conduit that the wave travels through, it is just a line.
16 The mechanical pulse radiating through the will obey all the laws of reflection and acoustics bouncing off each surface giving up some energy of each bounce in mode changes and heat.


Reflection of sound waves
Reflected sound through a solid is a mechanical process and will follow all the law of physics. There is no smoke and mirrors or anything other than simple acoustics. Anyone who says or preaches that sound breaks the laws of physics; either does not understand sound waves or trying to sell something that is contrary to the truth.
1 The sound wave will radiate away from its source, until it hits an interface of different acoustic impedance.
2 The angle that the radiating sound wave comes into contact with the interface is the same and equal to the angle of reflection. The angle of incidence is equal to the angle of reflection.
3 Some of the sound wave energy will penetrate the interface.
4 Some of the sound wave energy will mode convert into a surface wave and run along its surface. This wave will radiate on the surface from its source. If it strikes reflector, it will follow the same laws of reflection. This reflected sound will travel in one direction radiating away from the reflector. This sound wave will not change direction unless it strikes another reflector. This reflected sound wave will not retrace its steps through its mode conversion.
5 Some of the energy from the sound wave will cause the interface to ring and diffracted sound waves to be emitted, radiating from this secondary source.
6 When the sound wave hits a reflector that is perpendicular to the sound wave propagation, the sound wave will reflect back in the opposite direction with a wave front radiating from the reflector.
7 The reflected radiating sound wave will carry on the one direction unless is strikes another surface to reflect off.
8 When the reflector is convex the sound wave will reflect in all directions.
9 When the reflector is concave the sound wave reflection will be focused to radios point of the curvature, then the sound wave will radiate from the focal point.
10 When the sound wave a surface breaking reflector. The sound wave will reflect off both surfaces following the laws of reflection and as the gets into the corner the reflected sound will spike into a focused angle of half the angle that of the reflector. It is like placing speakers in the corner of the room set at 45 degrees using the acoustics of the room to get most from the sound.

Received sound waves

The piezoelectric transducer receiver will convert mechanical energy into electrical energy.
First we must look at transducer. Albeit a disc or rectangle, they all have their sweet spots.

1 A sweet spot is an area of the transducer that is most efficient at turning mechanical. The areas are the centre and the rim. The antinode areas are dull spots that take more energy to produce the same voltage. The transducer is not linear across its face.
2 Add to this a wedge of plastic with its varying thickness and linearity is thrown out even further. Now the centre sweet spot will be lower than the centre.
The transducer is most efficient at converting the retuning sound into electricity when the sound wave impacts the face of the transducer square on.
3 The efficiency of conversion is reduced with each degree away from normal. There is a finite range of angles of returning sound waves can be turned into electricity.
4 This range of listening angles is also known as Beam Spread.
5 There are many variables that may range of angles, for example the type of transducer, the transducer backing, the design of the wedge and even the age of the equipment. All these variables cannot be calculated by formula.
6 To know the range of angles the each transducer and wedge combination must be measured empirically. The small side drilled hole is one of the best methods.
7 Corner reflectors are a should not be used to measure the listening angle range of Beam Spread as the corner reflector set at right-angle has a reflecting sweet spot of 45 degrees, The sweet spot of any planar surface connected reflector is at half the connecting angle.
8 The reflection from sweet spot is disproportionately high, as the sound wave has been focused into a straight line.
9 The strength of focused reflecting sound wave has the power to excite the transducer, even though the angle of incidence is outside of the normal range of listening angles. For example on a 1” or 25mm thick calibration block a 60 and 30 degree probe will be able detect this 45 degree reflection.
10 If this is not known and understood by the technician, the technician will plot and the reflector in the wrong position. When the technician knows the position of the reflector, the trig numbers do not calculate with the angle of the probe.
11 In Britain they calculated that the 60 degree beam would hit the vertical reflector, the beam would hit at the critical angle mode convert to a compression wave and the beam would travel down the vertical face and reflect back off of the back wall. Then the sound would retrace its steps turn back into a 60 degree shear wave beam and head back to the probe.
12 While in Germany they looked at the 30 degree probe picking up the 45 degree reflection from the corner reflector and the “creeping wave” was born.
13 The errors were made by the belief that the sound is a beam and not a wave front radiating. Drawing sound as a line is an excellent tool for drawing defects but it confused people into thinking sound is a line and when the line didn’t line up with the reflector, the drew in a second to connect the first line to the reflector. Now the numbers don’t add up, so the velocity had to change to bring it into line.
14 Just a simple thing, drawing the sound as a straight line had led to a chain of errors and some fantastic conclusions.
15 Most technicians that understand sound propagation dismissed it as stupidity. I remember on a 3 month advanced sizing course, a fellow student had a stand-up argument with the instructor, dismissing the idea of the sound bending back towards the probe as if the sound had intelligence. Other followed blindly believing everything that was told.
16 These mistakes were made over 30 years ago. If only they had 2 or more notches close together they may have come up with a better conclusion, or even a more fantastic one.
17 To perpetuate these mistakes is not being professional. So called experts selling pseudo-science of a ID creeping wave to the oil and power industries is in my opinion a massive lawsuits waiting to happen, when the engineers who understand physics wise up and see that “The Emperor Has No Clothes”.

    
 
 Reply 
 
Michael Moles †2014 *1948
, Joined ,
17:31 Jan-08-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 21:08 Jan-07-2011 .

Andrew:
As per your request, we are sending you a video on creeping waves for you. This video belongs to Ed Ginzel of Materials Research Institute in Waterloo, Ontario, Canada.
Yours,
Michael Moles

    
 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
20:37 Jan-09-2011
Re: Proof of creeping wave?
In Reply to Michael Moles †2014 *1948 at 17:31 Jan-08-2011 .

The video shows a sound wave front radiating from the transducer.
The wave front is following the laws of reflection as each part of the wave front bounces off the internal surface.
THERE IS NO CREEPING WAVE IN THE VIDEO

    
 
 Reply 
 
Michael Moles †2014 *1948
, Joined ,
21:04 Jan-09-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 23:18 Dec-15-2010 (Opening).

Andrew:

No video; NDT.NET would not allow posting. Please send me your mailing address.

Yours,
Michael Moles
Olympus NDT

    
 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
21:14 Jan-09-2011
Re: Proof of creeping wave?
In Reply to Michael Moles †2014 *1948 at 21:04 Jan-09-2011 .

I HAVE SEEN THE VIDEO AND IT SHOWS NO CREEPING L WAVE AND NO 31 DEG REFLECTION

    
 
 Reply 
 
Rolf
Director,
NDT.net, Germany, Joined Nov 1998, 605

Rolf

Director,
NDT.net,
Germany,
Joined Nov 1998
605
00:42 Jan-10-2011
Re: Proof of creeping wave?
In Reply to Michael Moles †2014 *1948 at 21:04 Jan-09-2011 .

Michael,

Of course we can show the video, just tell me where I can download the file so that I can provide s streaming version.

Rolf

    
 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
01:33 Jan-10-2011
Re: Proof of creeping wave?
In Reply to Rolf at 00:42 Jan-10-2011 .

http://www.autsolutions.net/Creeping-waves.html

    
 
 Reply 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 298

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
298
08:26 Jan-10-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 23:18 Dec-15-2010 (Opening).

Hi Guys,
I have had an example of what I believe to be "creeping waves" (in fact two examples).
I believe these to be surface waves.

Example 1. Pulse echo inspection of a large forged ring, with longitudinal (ultra)sound impinging on a concave radius at a tangent after having passed through one part of the component. We detected a defect indication some distance past this radius where the "straight beam line" from the probe had continued "in a straight line". (Our test was aimed at detecting cracking in the radius).
Investigation of this sample showed that the defect (real defect) was in fact in the surface as a continuation of the radius. We proved the indication by damping on the surface between the radius and the defect, and showed that the defect indication disappeared.
Explanation? I believe that the longitudinal wave impinging on the radius converted to a longitudinal surface wave and followed the surface contour.
How does the sound know when to change back to longitudinal wave?
It doesn't but it radiates longitudinal wave all the time, and when going back around the radius, some sound will radiate back along the incident beam line to the probe.

Example 2. "Delta Z" immersion inspection technique. In this technique, a very short focus probe is brought very close to the surface of the component being inspected. Closer than the focus.
Some of the sound energy (if the focus is small enough) will impinge on the surface (in a ring) at an angle which converts to 90 degree longitudinal wave. This will continue to propagate accross the diameter of the circle, radiating sound energy back out at the incident angle all the time, but when it reaches the other side of the circle, it is then ideally placed to be detected on the other side of the probe. Surface breaking defects in any orientation within the small circle being inspected will then reduce the amplitude of the sound propagating past, and therefore reduce the amplitude of the received signal. These experiments were at 50MHz on ceramic materials, but have also been proven on metallic samples.

Conclusion.
These "creeping waves" are 0 degree longitudinal (or shear) waves, generated as per Snells Law, and they radiate their energy all the time as they propagate. this means that the apparent attenuation is very high, but the condition does exist.

Godfrey

    
 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
03:31 Jan-11-2011
Re: Proof of creeping wave?
In Reply to Godfrey Hands at 08:26 Jan-10-2011 .

Evidently you are coming to your conclusions via calculations as did NDT colleagues Hermann Wuestenberg and others.
On this side of the pond, the so called experts teach sound as a beam. They teach the sound will travel down a beam. The sound hits the underside AKA ID, mode covert to a compression wave and travel along the underside. If the compression wave hits a reflector, the compression wave will travel back until it reaches the place where it had mode changed from the shear and then this time it will re-mode convert to the shear. (Is it getting to sound stupid to you, bendy sound with a memory).
I am asking for VIDEO evidence of this phenomenon, I and others have huntend on the net for one to no avail, so until then the “The Emperor Has No Clothes”

    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1260

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1260
13:56 Jan-11-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 23:18 Dec-15-2010 (Opening).

Andrew, if I read it correctly, your concern is for the misuse of the "concept" of the so-called creeping wave; in particular the so-called "ID creeping wave".
Perhaps we can concur on the phenomenon that occurs at the near surface with the high angle comprssion mode. Some like to call this the "OD creeping wave". For many years it has been identified as the "lateral wave" in TOFD. We use the same nominal refracted angles to produce the effect people are calling the "near surface creeping wave" in pulse-echo applications. These are extremely well explained long ago on NDT.net (http://www.ndt.net/article/ecndt02/195/195.htm) by Marklein et al (see Fig. 3 in that reference).
The concept of the "so-called ID creeping wave" seems to have come out of teachings from EPRI (UT Operator Training of INtergranular Stress Corrosion Cracking-Competency Area 911) in about the mid to late 1980s. Module 4 discussed the 30-70-70 method and explained the "Opposite Surface Phenomena" by using the Law of Reciprocity. But connecting the signal identified as the "Creeping Wave Signal" to the mode conversion of shear to compression seems like a red-herring. The signal origin is merely the corner effect of the shear mode (both the headwave and the Snell calculated). It is most unfortunate that the training module (e.g. Figure 1 in the old EPRI module 6) identified the late arriving signal from the opposite surface as the "creeping wave" when a simple conversion to time could have identified the real mode as shear. Calling the near side compression mode signal and the far side shear mode signal both a "creeping wave" implied these were both of the same "Mode". We now see quite clearly that they are not originating from the same mode.

    
 
 Reply 
 
David Mackintosh
Engineering,
Acuren Group Inc., Canada, Joined Feb 2011, 85

David Mackintosh

Engineering,
Acuren Group Inc.,
Canada,
Joined Feb 2011
85
21:56 Jan-11-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 23:18 Dec-15-2010 (Opening).


Creeping wave experiment

Is the ID reflection from a corner trap or creeping wave? There must be some experiment that can tell us. A video may not show micro-phenomena at the surface. I propose the experiment below. Perhaps someone with more UT knowledge can suggest a better one.

Create a block with a slot that just shades the corner from the direct beam. The slot is also slanted so it does not return any beams. Maybe fill the slot with some dampening material. The shear wave beam goes in behind the slot and is lost, i.e. there is minimal corner trap signal. If there is a creeping wave it will creep along the surface, hit the corner, and come popping back out again, the way creeping waves are supposed to do, unless I have misunderstood.

David
    
 
 Reply 
 
Phil Herman
Sales, - Manufacture of NDT Reference Standards/Test Blocks
PH Tool Reference Standards, USA, Joined Oct 1999, 79

Phil Herman

Sales, - Manufacture of NDT Reference Standards/Test Blocks
PH Tool Reference Standards,
USA,
Joined Oct 1999
79
22:28 Jan-11-2011
Re: Proof of creeping wave?
In Reply to David Mackintosh at 21:56 Jan-11-2011 .

If someone is willing to perform the experiment that David suggested, I'd be willing to make the proposed block with the angled notch...in the spirit of science that is.
Phil Herman
PH Tool Reference Standards

    
 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
00:56 Jan-12-2011
Re: Proof of creeping wave?
In Reply to Ed Ginzel at 13:56 Jan-11-2011 .

Ed
Thanks for your input.
I don’t find it strange that no-one can produce a video, as there is none. I am in total agreement with you that, that the reflection from the ID connected corner has been mistaken, misplaced and miscalled as a creeping wave. Anyone that understands PAUT would have seen on the S scan that there is no creeping wave. So way didn’t anyone who knows PAUT call it out as a “Con”? Do you think that the Oil and Power industry will take legal action against the NDE companies that have been participating (for want of a better word) fraud. This may sound strong, but at times this is a tough job, if we don’t keep to the scientific facts and stamp out pseudo-science, how can we keep our integrity?

    
 
 Reply 
 
Ryan Burns
Ryan Burns
05:48 Jan-12-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 00:56 Jan-12-2011 .

Andrew,

Before litigation, I think it's important here to point out that the technique, while having a misleading name, still works, and works very well when used correctly.

Regards,

Ryan.

    
 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
21:32 Jan-12-2011
Re: Proof of creeping wave?
In Reply to Ryan Burns at 05:48 Jan-12-2011 .

Hi Ryan

If I sold you a ticket to be chauffeured from Edmonton to Calgary in a Mercedes Benz for $1000.00 then put you on the Greyhound. If you protest that it is was not a Mercedes and my reply was “ I got you to Calgary” would you say I was of high integrity or would you call me a con man?

Am I wrong to try to maintain the integrity of our profession?

    
 
 Reply 
 
Ed Mawyer
Consultant, Level III
USA, Joined Jan 2011, 1

Ed Mawyer

Consultant, Level III
USA,
Joined Jan 2011
1
14:22 Jan-18-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 21:32 Jan-12-2011 .

I dont think anyone performing any inspection where you have a known defect, can find it consistently, and then utilzes the method in which they found it to perform an inspection should be called a fraud. Whether its called a "creeping wave" or peanut butter and jelly technique, what I, and the customer should care about is finding the discontinuities. If the said method is not reliable, that is another story.

I do agree, the only thing we have as NDT professionals is our reputation and unfortunately the reputation of the entire industry but I dont think there are enough people outside of NDT that understand enough to allow science (or the mislabeling of a technique) to be a factor. Unfortunately, most of our customers view us as a requirement, and arent really concerned with the safety associated and could care less about the science. (Untill you've found something and have to explain why you did, and how you are sure)

    
 
 Reply 
 
Rolf
Director,
NDT.net, Germany, Joined Nov 1998, 605

Rolf

Director,
NDT.net,
Germany,
Joined Nov 1998
605
16:37 Jan-18-2011
Re: Proof of creeping wave?
In Reply to Phil Herman at 22:28 Jan-11-2011 .

I am wondering if a simulation tool could proof this case, e.g. CIVA could do this job?

    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1260

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1260
17:35 Jan-18-2011
Re: Proof of creeping wave?
In Reply to Rolf at 16:37 Jan-18-2011 .

Good idea Rolf! CIVA 10 has made a provision to deal with the so-called creeping wave. I will ask the people in EXTENDE if we can configure a suitable model.
As for Dave MacIntosh's suggestion that this might be a "micro-phenomena" I would suspect not...if it is too small to 'see' photoelastically it would imply a very low sound intensity. This would imply a very weak signal. Yet the commonly labelled "ID creeping wave" is illustrated as the largest of the three signals and the latest arrival when illustrating the detection of the far-surface connected notches. One optoin is to simply convert the timebase to microseconds and measure the peak arrival times and measure the distances travelled (and know the time travelled in the wedge)...

    
 
 Reply 
 
Deston Henson
NDT Inspector,
Canada, Joined Nov 2009, 20

Deston Henson

NDT Inspector,
Canada,
Joined Nov 2009
20
04:52 Jan-19-2011
Re: Proof of creeping wave?
In Reply to Ed Ginzel at 17:35 Jan-18-2011 .

Hello All,

Out of curiosity, are there any responses from the people who teach creeping wave on this discussion thread?

Many thanks,

    
 
 Reply 
 
Frits Dijkstra
R & D
Applus RTD Technological Center, Netherlands, Joined Jan 2004, 6

Frits Dijkstra

R & D
Applus RTD Technological Center,
Netherlands,
Joined Jan 2004
6
17:12 Jan-19-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 23:18 Dec-15-2010 (Opening).

Download mp4 simulation 1 (~4 MB)

Download mp4 simulation 2 (~4 MB)

Download mp4 simulation 3 (~4 MB)

Triggered by the discussions in this forum, I had some interesting discussions with some of the physicists in our department. As a mechanical engineer trained in ultrasonics, I also tend to "think" in terms of beams and rays, as in optics. But physicists think in wave fronts. They convinced me that this is the only way to understand and describe this kind of complex concepts. Together, we have tried to provide some answers acceptable for ultrasonic engineers as well as physicists. We also ran some Finite Difference (FD) computer simulations for support. These are directly based on the wave equation, so all phenomena such as refractions, diffractions and wave mode conversions are automatically included. Longitudinal and shear waves are visualized in different colors.

Simulation 1 shows a 16 mm thick steel plate with a 5 MHz probe on it (16 mm crystal). The angle in the wedge is for 90° longitudinal waves and 33° shear waves.
The incident longitudinal wave front in the wedge (blue) is reflected back into the wedge, and is also refracted into a longitudinal wave front in the steel plate (blue). This wave travels along the plate surface and also spreads out into the material. This wave at the surface is what we are used to call creeping wave. In ToFD we call it the lateral wave. Maybe we should just call it a 90° longitudinal wave. In addition, we see the shear wave (red) in the steel plate that goes with it, propagating under 33°. At the back wall, this wave is converted into another 90° longitudinal wave ("secondary creep wave") and a shear wave associated with it.

Note that, at the scanning surface, even in front of the probe, where the "driving force" (the original incident wave in the wedge) is not present any more, there is still a shear wave associated with the propagating 90° longitudinal wave. Some call this a "head wave". This wave keeps accompanying the 90° longitudinal wave, while it travels along the surface. It is not a beam, but a straight wave front propagating under 33°. In the past I was taught that this wave is due to interaction between the propagating 90° longitudinal wave and the plate surface. Our physicists explain it as follows:

"At an interface between two media, be it the probe against the plate or air against the plate, there should be continuity in the displacement and the stresses in the media, across the interface. These continuity requirements, also called boundary conditions, determine the reflection, transmission and conversion coefficients between waves on either side of the interface.
In the case of the FD model shown it means that a longitudinal wave propagating under 90°, along an air/steel interface, cannot fulfill the boundary conditions without an accompanying shear wave propagating under the appropriate angle. Rather than thinking in terms of cause and effect, we should say that both waves should be present in order to satisfy the physics of this problem".

In simulation 2, the probe is placed at the correct position for corner effect on a 3 mm notch, using the 33° shear wave. The simulated A-scan is shown below in the movie. Although 33° is not an ideal angle for corner trap effect, the notch is clearly detected.

In simulation 3 the probe has been pulled back some 20 mm, to prevent the direct corner trap echo from getting back to the probe. But the notch is still detected:

1. A 33° shear wave originates from the probe. It keeps coming even in front of the probe. The wave front hits the far surface, reflects into a 33° shear wave front and is also converted into a 90° longitudinal wave at the far surface. This wave is also called the secondary creeping wave.
2. At the frame taken at 14.23 µs, this 90° longitudinal wave hits the notch and is reflected back to the left, along the far surface.
3. Along with this reflected 90° longitudinal wave we see a shear wave front, propagating towards the scanning surface under 33°, which is continuously accompanying the longitudinal wave.
4. Interesting to see that this shear wave in turn is able to make a 90° longitudinal wave at the scanning surface, traveling to the left.
5. The shear wave front mentioned under 3 together with the 90° longitudinal wave under 4 is able to reach the probe and results in a signal (indicated by an arrow in the A-scan).

These simulations suggest that the combination of 90° longitudinal waves and its associated 33° shear wave is able to detect a vertical defect at the far surface. This is also the case (but with a lower signal amplitude) if the probe is pulled back to such an extent that the direct corner trap echo is not returning to the probe any more. In other words: this is the proof of the secondary creeping wave. By the way: the shear wave crucial for detection with the secondary creeping wave is also visible in the video by Blanshan and Ginzel, posted earlier, see the yellow arrow we added.




So, it looks like Wüstenberg and Erhard were right after all. To be precise, the first to describe these phenomena was a Russian scientist, Prof. I.N. Ermolov, in 1978.

Finally: there is a lot of confusion about naming of these phenomena. In general (not only in this forum), this confusion complicates the discussion.
    
 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
03:57 Jan-20-2011
Re: Proof of creeping wave?
In Reply to Ed Mawyer at 14:22 Jan-18-2011 .

Peanut and jelly method, as it is taught, states that the shear wave will mode convert to a compression wave and propagate forward for a short distance, (contradiction #1 a compression wave is the most effective/ efficient way of transmitting sound) Then compression wave hits a ID connected reflector and reflects and a compression wave, until it reaches its initiation point and mode converts back to a shear.
If this were true, “peanut and jelly method” would never miss a defect.(#2 WRONG. If the reflector is at an oblique angle there can be NO refection to the transducer.)
The peanut and jelly can and does miss cracks if they are at the wrong angle…

    
 
 Reply 
 
Andrew Cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

Andrew Cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
21:01 Jan-20-2011
Re: Proof of creeping wave?
In Reply to Frits Dijkstra at 17:12 Jan-19-2011 .

Thank you for correcting my error and my apologies to Prof. I.N. Ermolov, for not giving him the credit.
BUT “The Emperor STILL Has No Clothes”
The video shows.
A high angle compression wave front (as pre Snell’s law) propagating away from the probe. Not disputed.
A lower angle shear wave front (as per Snell’s law) propagating away from the probe. Not disputed.
A shear wave bouncing off the ID (as per laws of reflection). Not disputed.
A reflected shear wave returning to the probe at a different angle than probes optimum listening angle.
It does not show a second compression wave (creeping wave) propagating at twice the velocity at the point of impact and proergating at 90 deg.
It does not show the second compression wave (creeping wave) reflecting back at 90 deg.
It does not show the second compression wave (creeping wave) mode converting to a shear wave at the original impact.

    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1260

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1260
21:50 Jan-21-2011
Re: Proof of creeping wave?
In Reply to Frits Dijkstra at 17:12 Jan-19-2011 .

Frits: Many thanks for the FD illustration videos. The FD tool is a nice convergence of mathematics and physics! These videos are more effecctive than the semi-analytical options for showing the details of the surface interactions.

    
 
 Reply 
 
Stan
NDT Inspector,
Canada, Joined Jan 2009, 31

Stan

NDT Inspector,
Canada,
Joined Jan 2009
31
19:51 Jan-31-2011
Re: Proof of creeping wave?
In Reply to Frits Dijkstra at 17:12 Jan-19-2011 .

Frits:
These simulations of ID surface Creeping Wave propagation were very enlightening, however, the company that I work for does a lot of Near Surface Creeping Wave examinations. We use this method to examine the toe and root area of fillet welds where the probe is placed tangent to the fillet weld and sound is propagated under the fillet.
Would you be able to run and publish a simulation with a flaw on the near surface of the item being examined, about 10 to 20mm from the front of the probe?
Regards.

    
 
 Reply 
 
Frits Dijkstra
R & D
Applus RTD Technological Center, Netherlands, Joined Jan 2004, 6

Frits Dijkstra

R & D
Applus RTD Technological Center,
Netherlands,
Joined Jan 2004
6
15:13 Feb-02-2011
Re: Proof of creeping wave?
In Reply to Stan at 19:51 Jan-31-2011 .

Stan,

Usually, for such simulations, there is some cost involved. I have discussed your question here, and we will make an exception for the sake of this Forum discussion about creeping waves. I think we all can learn from this.
So, yes, we will be able to run this particular simulation for your fillet weld problem and publish it here on the Forum.

Please send me an e-mail with all parameters: geometry and dimensions of the object, location, size and shape of the defect, location of probe index, crystal dimension, probe frequency. A sketch would help. Based on this information we will build the model and run the simulation. I hope it is not a problem if it takes a week or two, due to the current work load.

Best regards, Frits
frits.dijkstra@applusrtd.com

    
 
 Reply 
 
David Mackintosh
Engineering,
Acuren Group Inc., Canada, Joined Feb 2011, 85

David Mackintosh

Engineering,
Acuren Group Inc.,
Canada,
Joined Feb 2011
85
18:06 Feb-02-2011
Re: Proof of creeping wave?
In Reply to Frits Dijkstra at 15:13 Feb-02-2011 .

Frits:
Thank you for the very interesting discussion and video simulations. On this controversial topic, would you consider publishing a peer-reviewed paper on your findings? In particular, what is the velocity of the wave you observed, and is it different from a Rayleigh wave, a Stonely wave, or the TOFD lateral wave? Perhaps some collaboration would be helpful to verify your results experimentally.
Many thanks,
David

    
 
 Reply 
 
Rolf Diederichs
Director,
NDT.net, Germany, Joined Nov 1998, 605

Rolf Diederichs

Director,
NDT.net,
Germany,
Joined Nov 1998
605
18:27 Feb-02-2011
Re: Proof of creeping wave?
In Reply to David Mackintosh at 18:06 Feb-02-2011 .

David,

why you asked for a peer-reviewed paper?
In NDT.net we are publishing editor reviewed paper which are published faster than peer-reviewed papers and also having good quality AND the best of all those are open access available.

Rolf

    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1260

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1260
21:50 Feb-02-2011
Re: Proof of creeping wave?
In Reply to David Mackintosh at 18:06 Feb-02-2011 .

David...this has all be done before. If you need a scholarly explanation you can look at a very old paper
On the Nature of the So-Called Subsurface Longitudinal Wave and/or the Surface Longitudinal “Creeping”Wave, K.J.Langenberg, P. Fellinger, R. Marklein, Research in Nondestructive Evaluation, Springer-Verlag, 1990, pp 61-81
This uses the EFIT process instead of the Finite Difference but the end result is the same.
In a 2008 paper on NDT.net by Professor Honorvar (http://www.ndt.net/article/tindt2008/papers/150.pdf) I provided some photoelastic images of the effect of the near side process Stan is asking about. Look at Figure 7 in that paper.

    
 
 Reply 
 
Lalit Mohan Kothari
Consultant, -
On ..IOCL and BARC(Bhabha Atomic Research Centre).etc, India, Joined Jan 2003, 128

Lalit Mohan Kothari

Consultant, -
On ..IOCL and BARC(Bhabha Atomic Research Centre).etc,
India,
Joined Jan 2003
128
14:57 Feb-04-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 23:18 Dec-15-2010 (Opening).

Dear all,
As probe has its size and wave itself reflected between its body and
as probe become old and shoe; shape changes some grass observed and it can be checked by just dumped by the your finger from the front side of probe …
so for me Besides of critical angles …..the wave also reflected from the body of probe
and mod conversion is always their
This angle can also enhance the creeping wave theory

Thanks for live

Lalit Mohan Kothari

    
 
 Reply 
 
Andrew Cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

Andrew Cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
20:24 Feb-12-2011
Re: Proof of creeping wave?
In Reply to Frits Dijkstra at 17:12 Jan-19-2011 .

Thanks for the great vedios
I have watched the video a few times and I am perplexed that why you are calling the wave front that is propagating from the compression wave solid to air interface. This wave motion is 0 degree shear in direction and 33 degree wave front. The angle is determined by the ratio of the 2 velocities. i.e. if the velocities were the same, one would have a 45 degree wave front which is traveling at 90 degrees to the surface, behind the radiating compression wave.
You call the reflecting compression wave 90 degree where it is a reflection that is RADIATING.
The corner trap reflector that are shear wave were reflecting back at 45 degrees but when it reaches the transducer this shear wave you called them creeping wave.

    
 
 Reply 
 
Frits Dijkstra
R & D
Applus RTD Technological Center, Netherlands, Joined Jan 2004, 6

Frits Dijkstra

R & D
Applus RTD Technological Center,
Netherlands,
Joined Jan 2004
6
19:06 Mar-03-2011
Re: Proof of creeping wave?
In Reply to Stan at 19:51 Jan-31-2011 .

Download mp4 Model 1 - reference no defect [~1MB]

Download mp4 Model 2 - with 1 mm high defect [~1MB]

Stan,

Further to your contribution of last January 19 we have done two simulations on the geometry you proposed.


Model 1 - reference no defect


Simulation 1 uses model 1. We see a 19 mm thick pipe wall. At the outside, a 13 mm thick repad has been attached, by means of a fillet weld. We have assumed a 0,5 mm gap between pipe wall and repad.

The probe is a 5 MHz creeping wave probe with an element height of 0.51" (only element height is relevant here, because we have used a 2D simulation). The probe has its index at a distance of 10 mm from its front. Probe front is 5 mm away from the weld. This probe is designed to produce a creeping wave as well as a longitudinal wave beam under approx. 75°.


Model 2 - with 1 mm high defect


Simulation 2 uses model 2 which is identical to model 1, with the only difference that we now have a 1 mm high defect at the location as indicated. In both simulations, longitudinal waves are blue and shear waves are red.

In simulation 1, we have manually added some arrows in the first 19 frames, which refer to the "usual" way of showing ultrasonic waves, by means of rays. The blue arrows are longitudinal waves (creep and 75° beam), red is the shear wave under 33°. After the longitudinal and shear wave beams have been fully formed they tend to stick together, but move horizontally with the propagation of the creeping wave. Eventually the shear wave front will result in a "secondary" creeping wave as previously discussed.

The situation changes as soon as the creeping wave at the OD reaches the weld and looses the surface. This happens in the frame at 5.90 µs. From now on the longitudinal wave and the shear wave are independent bulk waves, without interaction at the surface. Note that the creeping wave does not follow the weld contour.

After the longitudinal wave has reached the tip of the gap (frame at 7.96 µ), a very weak echo (blue) is reflected. This will eventually reach the probe as a very weak signal, indicated by the red arrow in the A-scan at the bottom. This signal's amplitude will depend of the gap width and the shape of the gap's tip.

In simulation 2 the situation is identical to the one in simulation 1, until the longitudinal wave has reached the defect (frame at 7.96 µs). The reflected longitudinal wave will propagate as a bulk wave, until it has passes the weld and reaches the pipe's OD surface. At that moment, part of it is reflected against the weld geometry and reflects back to the defect. The other part will now propagate along the pipe's OD surface, will interact with that surface, so it is a creeping wave again, even with an associated (red) shear wave. As soon as it reaches the probe, the 90° creeping wave will enter the probe under an angle according to Snell's law and will eventually reach the receiver. The signal is indicated by an arrow in the A-scan at the bottom.

These simulations confirm that a defect in the root of a fillet weld can be detected by means of creeping waves. They show very nicely that a creeping wave is only a creeping wave as long as it propagates along a surface.

If there are any questions or comments please let me know.

Best regards, Frits

    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1260

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1260
21:47 Mar-03-2011
Re: Proof of creeping wave?
In Reply to Frits Dijkstra at 19:06 Mar-03-2011 .

Fritz...again, nice simulation of the glancing compression wave that some call the creeping wave.
But you state "Note that the creeping wave does not follow the weld contour". I draw your attention to the frame at 5.9us. At this point the compression wave that is boundary-locked to the test surface reaches a sharp corner and diffracts as a spherical wavefront. But the contact point of the compression wave is also the initiator of the shear headwave and that too is "tip diffracted" by the corner. Both the compression mode and shear mode corner-diffractions now have a component that is moving parallel to the curved surface. Note how the tip-diffracted compression wave continues to generate the shear headwave even as it rounds the corner and moves up the radius (weld). Note how the headwave off the compression wave is now curved. The tip diffracted shear wave also moves as a glancing wavefront at the boudary. Both the shear headwave from the corner diffracted compression mode and the glancing shear mode moving along the weld radius are clearly seen at 6.67us.
But what is also interesting to see in this FD simulation is that by 8.73us there is a well formed Rayleigh wave lagging the tip-diffracted shear wave that formed from the shear headwave moving off the 19mm plate surface. By 9.75us the Rayleigh mode is distintly formed and any link to the initiating corner (tip)-diffracted shear mode is difficult to see.
This diffraction effect of the compression mode at a corner provides the principles used in TOFD Tee weld inspections.

    
 
 Reply 
 
Stan
NDT Inspector,
Canada, Joined Jan 2009, 31

Stan

NDT Inspector,
Canada,
Joined Jan 2009
31
16:23 Mar-08-2011
Re: Proof of creeping wave?
In Reply to Frits Dijkstra at 19:06 Mar-03-2011 .

Frits:
Thanks for these simulations, they will prove to be invaluable teaching aids for the technicians that I work with. There are few UT inspection methods that are more difficult for new technicians to understand than Creeping wave and these will help a great deal.
Regards
Stan

    
 
 Reply 
 
Alexandros
Alexandros
02:47 Mar-17-2011
Re: Proof of creeping wave?
In Reply to andrew cunningham at 23:18 Dec-15-2010 (Opening).

i hope this helps mate...

http://www.youtube.com/watch?v=jBEV3lRPNJY&feature=related
http://www.youtube.com/watch?v=sbFOkRjDON0&feature=related
http://www.youtube.com/watch?v=NJ4Q_x9bvI4&feature=related
http://www.youtube.com/watch?v=PPBKjSRTwqs&feature=related
http://www.youtube.com/watch?v=FGntdiWhvHw&feature=related

in some parts you can see what may be call as the first critcal angle (creep wave)
i dunno, im not a doctor.

    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1260

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1260
12:18 Mar-17-2011
Re: Proof of creeping wave?
In Reply to Alexandros at 02:47 Mar-17-2011 .

Alexandros, the videos you noted are made using the schlieren visualisation system made by Onda. When well aligned (as in the Onda setup) the images can be very bright. The samples used in the videos are metal (aluminium) tubes so we cannot see the effects within the tube itself. Another problem with the schlieren technique is that it cannot visualise shear mode. Similar movies as those shown in the videos you noted were produced wtih pulsed (and CW) laser schlieren systems in Battelle labs and Sperry's Automation Industries (circa 1974 and 1970). Without the ability to see into the samples and since the shear mode is not visible due to the nature of the way in which schlieren imaging occurs, we will not be able to see the the shear mode and the formation of the shear headwave discussed in this thread. However, there are many other useful links on Youtube that can provide useful illustration of the effects...e.g. http://www.youtube.com/watch?v=L9ax0BoIle4&feature=related
There you will find several demos from the finite element software called PZFlex

    
 
 Reply 
 
A.otoom
,
Saudi Arabia, Joined Jul 2011, 13

A.otoom

,
Saudi Arabia,
Joined Jul 2011
13
19:03 Jul-26-2012
Re: Proof of creeping wave?
In Reply to Frits Dijkstra at 19:06 Mar-03-2011 .

I would like to really thank you for this powerful and useful discussion
But in fact I have a inquiry about calibration creeping wave!!
Is it the same way used in the calibration of the angle beam(P/E) or is it different?

BEST REGARDS
A.OTOOM

    
 
 Reply 
 
Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 409

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
409
00:47 Jul-28-2012
Re: Proof of creeping wave?
In Reply to A.otoom at 19:03 Jul-26-2012 .

Otoom,
creeping wave calibration is similar to the shear wave but with procedures functional to application type and standards.
Some examples.
An application DNV-OS-F101 for surface and subsurface defects examination in tainless steels and nickel alloy welds require calibration signals with notches 0,5-1,0-2.0 mm depth. The signals provided have same beam path; only the amplitude changes in proportion to the depth. We do not have a curve but different amplitudes overlapped.
Application for clad flaw examination according ASME V provides holes SDH dn 1.5 mm at different depths in the clad thickness. Reflectors can be used for the construction of a DAC with different paths. The amplitude curve follows the focus beam.
I have found some reference reflector using notches for secondary creeping wave calibration (or in any other way we want to call them). This seems to me appropriate for applications with indications ID connected.
In all cases we are in pulse echo technique.
I hope maybe other members want to add application examples.
Greetings
Mario

    
 
 Reply 
 
Andrew Cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

Andrew Cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
02:39 Aug-08-2012
Re: Proof of creeping wave?
In Reply to A.otoom at 19:03 Jul-26-2012 .

The signal that is shown in the video simulations shown in this forum, some are calling creeping wave, but is just a Tip Diffraction signal, emanating (radiating) from the tip of the notch. The depthing of this signal, can be done by a well proven Tip Diffraction method with shear wave calibration. It may also be depthed by percentage of wall thickness, or with direct depth measurements. They are all accurate was of measuring. It is down to you what calibration method you use. Your task is to find and accurately measure and pass your results on to the party concerned.

    
 
 Reply 
 

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