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Raphaël MICHEL
R & D,
Vallourec, France, Joined Feb 2016, 8

Raphaël MICHEL

R & D,
Vallourec,
France,
Joined Feb 2016
8
13:51 Apr-18-2017
UT: relation between depth and amplitude

Dear all,

I have a very fundamental (and easy?) topic for UT experts.

We are using pulse echo UT with shear waves on seamless steel pipes to inspect surface defects (inside & outside surfaces, longitudinal and transverse orientations).

I know that theoretically, we are not supposed to detect defect smaller than λ/2.
But in practic, I can detect a 0.3mm-deep notch with a 2MHz probe (λ/2= 0.8mm) with correct performance.

Do you know the relation between depth, amplitude and wavelength? Is it like roughly linear on a specific domain, and then flat above a specific value?
Do other parameters (beam size? focus? refracted angle? etc.) have any influence?

Feel free to ask any question, this is a very open topic!
Thank you in advance for your replies!

Raphaël

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 756

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
756
04:08 Apr-19-2017
Re: UT: relation between depth and amplitude
In Reply to Raphaël MICHEL at 13:51 Apr-18-2017 (Opening).

Detection is limited by signal to noise ratio and not λ/2. So in clean fine grain materials you can see very small defects and only large defects in noisy/large grain materials

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 856

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
856
05:06 Apr-19-2017
Re: UT: relation between depth and amplitude
In Reply to Anmol Birring at 04:08 Apr-19-2017 .

Raphaël,

When we refer to the minimum size defect detectable, we don't refer to depth, we refer to the width of it. By having a notch as a reflector, I suspect you are working to the ASME code. The length of this reflector is more like 12 mm which is easily detectable with a 2MHz transducer.

The relationship you are talking about is very simple. The lower the frequency (so the bigger lambda), the deeper you will be able to detect reflectors. In other words, lower frequency provide you with more sensitivity. As well, deeper is the reflector, less will be its amplitude on the screen. Please refer to your DAC curve. We are talking to reflectors of equal size , but different depth.

As for resolution, that is the ability of a transducer to detect reflectors that are close by.

For your other question regarding the relationship between beam size, focus, refracted angle and all, I would suggest that you get transducers of different frequency and size and experiment. As well, you can simply use your ut formulas to see what effect each parameters have on you sound beam

 
 Reply 
 
Raphaël MICHEL
R & D,
Vallourec, France, Joined Feb 2016, 8

Raphaël MICHEL

R & D,
Vallourec,
France,
Joined Feb 2016
8
10:07 Apr-19-2017
Re: UT: relation between depth and amplitude
In Reply to Raphaël MICHEL at 13:51 Apr-18-2017 (Opening).

Thank both of you for your answers,

I guess I didn't give enough information. Please find here more data:

Codes: could be ASME, ASTM, ISO, API.

We are usually dealing with 25mm long notch (longer than beam size), N-type according to NF EN ISO 10893-10. These notches are located on the inside or outside surfaces, not within the material.

My topic is referring to the relation between defect depth (as defined in the ISO) and amplitude, not to the minimum detectable defect (which is also important, but another topic ;-) )

With defects 0.1mm, 0.3mm, 0.5mm, 1.0mm,1.5mm, 3.0mm deep, would the amplitude be linear, at least on a specific domain?

There might be no formula or rule. If that so, I'll make trials and simulations...

Best regards.

Raphaël



 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1282

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1282
15:23 Apr-19-2017
Re: UT: relation between depth and amplitude
In Reply to Raphaël MICHEL at 10:07 Apr-19-2017 .

zoom image
Raphaël, the relationship between a simple flat target and the amplitude is generally a simple proportionality based on the reflecting area relative to the element area. This is the foundation of the AVG system using flat bottom holes perpendicular to the beam and on axis with the beam.
However, with the notch conditions you are asking about the proportionality cannot be extended infinitely. I have provided a Civa simulation of a 45° beam scanning with its centre axis at the point that the notch meets the far surface in a 20mm thick steel plate. I simulated a 10mm diameter 5MHz probe with a 45° refracted beam in shear mode. Notches were 15mm long and had heights increase by doubling from 0.25mm to 8mm. The first few notch responses ALMOST indicate a doubling of amplitude with about 5dB increase from 0.25mm to 0.5mm and another 5dB from 0.5mm to 1mm. Then the increases get smaller with only about 4dB between the 2mm and 4mm notch heights. As we move from 4mm to 8mm the change is only 1.6dB.
The returning angle from the notch face to the probe is not the same for each point along the notch vertical face so echo-transmittance effects will have a bearing on the integrated amplitude contributions of the various points from the notch.

1
 
 Reply 
 
Raphaël MICHEL
R & D,
Vallourec, France, Joined Feb 2016, 8

Raphaël MICHEL

R & D,
Vallourec,
France,
Joined Feb 2016
8
16:04 Apr-19-2017
Re: UT: relation between depth and amplitude
In Reply to Raphaël MICHEL at 13:51 Apr-18-2017 (Opening).

zoom image
Ed,

Thank you for your reply and simulations!

I have a similar understanding. The energy reflected shall be propotionnal to the reflective area (thus propotionnal to the notch depth) until the reflective area is bigger than the acoustic beam (there is then no more energy to reflect! ).

However, with some quick trials, we noticed different behaviors, as seen on the attached files. These trials were performed in immersion, on external longitudinal notches. Probe is flat.
We have a quick saturation of the amplitude, on different dimensions.

Could that come from other effects? Diffraction on notch edges?
 
 Reply 
 
John Pitcher
John Pitcher
16:33 Apr-19-2017
Re: UT: relation between depth and amplitude
In Reply to Raphaël MICHEL at 16:04 Apr-19-2017 .

Raphael,
You will find very high responses from notches when using 45° beams. (corner trap effect.) compared to SDH's. As soon as your angles are not 45° then you require more and more gain. In practice you become over sensitive when calibrating with a 60° on a notch when compared to a SDH.
John

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1282

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1282
19:24 Apr-19-2017
Re: UT: relation between depth and amplitude
In Reply to Raphaël MICHEL at 16:04 Apr-19-2017 .

zoom image
Raphaël, John pointed out the issue of echo-transmittance I was trying to make when he referred to the difference in response you would get between a 45° and 60° beam. I re-ran the Civa model to illustrate this effect with 60°. The same set of notches run using a 60° probe do not have the same amplitude differences. From the 0.25mm to 0.5m the change is significant at just over 9dB. 0.5mm to 1mm the difference is almost 7dB. From 1mm to 2mm height difference it would be about 5dB and from 2mm to 4mm height the amplitude difference is only 3dB. The difference between the 4mm and 8mm notches is only 0.7dB. These differences were based on a flat plate...but in your case, the effect was measured on a notch at a full skip in pipe!

The wavefront from a probe is generally spherical, so even on a flat reflecting surface there is some change in the angle that a beam makes with a flat target over the extents of the target. On a cylindrical reflecting surface the situation is exacerbated and the curvature of the reflecting surface ensures that the wavefront interacting with the vertical target does so at a range of angles. In the Beamtool image attached you see the arc that has formed off the inside pipe surface. Obviously each point along that arc that interacts with the notch will do so at a slightly different angle from its neighbour. In addition to the arc reflected from the inside surface, part of the returned beam is also attributable to a reflection from the outer surface of the pipe prior to reflecting off the notch. This will present a totally different set of angles acting on the notch. For every diameter and thickness of pipe and nominal incident angle of beam, the combination of angles reflected by the notch will be different.
2
 
 Reply 
 
Vincent CHARDOME
R & D,
Vinçotte n.v., Belgium, Joined Mar 2001, 8

Vincent CHARDOME

R & D,
Vinçotte n.v.,
Belgium,
Joined Mar 2001
8
09:42 Apr-24-2017
Re: UT: relation between depth and amplitude
In Reply to Raphaël MICHEL at 16:04 Apr-19-2017 .

Hi,

one interesting article for you is:
A note on the smallest defect that can be detected using ultrasonics from E. Marianeschi & T. Tili.

As mentioned earlier, this will depend on a lot of parameters (frequency, material, depth, flaw type, SNR, ...).

One can quickly estimate the detection limit by looking at the amplitude response vs flaw diameter (similar to the amplitude/height charts) and then extrapolating towards 6dB above noise level using f.e. a log trendline. Depending on the configuration, one may go smaller than λ/2.

 
 Reply 
 
Cole
NDT Inspector
USA, Joined Oct 2009, 52

Cole

NDT Inspector
USA,
Joined Oct 2009
52
23:05 Apr-25-2018
Re: UT: relation between depth and amplitude
In Reply to Ed Ginzel at 19:24 Apr-19-2017 .

Ed,

What would be the differences in dB using a 2.25 MHz 70 degree transducer .625” x .750”?

-Cole

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1282

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1282
13:38 Apr-26-2018
Re: UT: relation between depth and amplitude
In Reply to Cole at 23:05 Apr-25-2018 .

Cole, are you asking me to re-run the Civa computation?
If so, for what specimen conditions; plate/pipe?, thickness?, material?
Any background as to why you would like the results?

 
 Reply 
 
Cole
NDT Inspector
USA, Joined Oct 2009, 52

Cole

NDT Inspector
USA,
Joined Oct 2009
52
21:03 Apr-26-2018
Re: UT: relation between depth and amplitude
In Reply to Ed Ginzel at 13:38 Apr-26-2018 .

Yes please.

I want to know at what point with the transducervsnd angle previously mentioned the notch depth doesn’t have a change in amplitude.

Debating inspection on PJP weld depth penetration inspection procedure that utilizes 20% and 40% deep EDM notches to distinguish 80% and 60% penetrations.

-Cole

 
 Reply 
 
Cole
NDT Inspector
USA, Joined Oct 2009, 52

Cole

NDT Inspector
USA,
Joined Oct 2009
52
21:37 Apr-26-2018
Re: UT: relation between depth and amplitude
In Reply to Ed Ginzel at 13:38 Apr-26-2018 .

Sorry, plates range from .250” - 1.000” thickness in increments of .125”. Material is ASTM A572 carbon steel.

-Cole

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1282

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1282
15:22 Apr-27-2018
Re: UT: relation between depth and amplitude
In Reply to Cole at 21:37 Apr-26-2018 .

zoom image
Cole
In your query you asked at what depth the notch has no change in amplitude. For the probe you are using it is far more complicated than simply the notch depth. Your probe (0.625 x 0.750) equates to about 16x19mm and, depending on the wedge dimensions, has a near zone in the steel about 50mm from the entry point. You also wanted to assess notch responses in plates ranging from 0.250” to 1.0” (about 6mm to 25mm). So for about the first 20mm of plate thicknesses you will be looking at notch responses in the near field.
Using just the 12.5mm (half-inch) plate we can see that the effect of working in the near field results in some of the smaller notches having amplitude greater than some of the larger notches. The echodynamic plot indicates that the response from the 0.25mm notch will be about 6dB higher than the response from the 1mm notch and amplitudes would then increase until the integrated reflecting area encompassed the entire beam. In the model we again used notches up to 8mm depth.
For thinner plate the minimum amplitude need not correspond to the 1mm notch and will depend on the specific characteristics of your probe’s near field. But you seem to have not considered the fact that amplitude is based on the total reflecting area. In the plot called "echo-dynamic at 1mm notch" I ran 2 scenarios, one with the notches 15mm long (red line) and one where they are 20mm long (black line). For the same "depth" of notch using your probe with its relatively large beam area, you will also get a larger amplitude for notches that are longer even though they are the same depths.

Using such very large aperture probes would not be recommended for thin plate weld inspections.
It is perhaps also worth noting that the standoff (i.e. exit point to the maximum notch response) is not the same for all notches, and changes by about 2mm from the smallest to the largest notch. If you are really trying to assess depth of penetration, perhaps a small diameter high frequency probe with a 45° refracted angle would be better as it would provide an opportunity to assess the penetration by the upper tip echo arrival time as compared to the corner reflection.
 
 Reply 
 
Cole Williamson
NDT Inspector
USA, Joined Oct 2009, 52

Cole Williamson

NDT Inspector
USA,
Joined Oct 2009
52
16:42 Apr-27-2018
Re: UT: relation between depth and amplitude
In Reply to Ed Ginzel at 15:22 Apr-27-2018 .

Thank you Ed,

I had already arrived at the same conclusion and have always inspected depth of penetration by the upper tip echo arrival time.

I just seen a procedure written employing EDM notches and was just trying to prove what I and you have already concluded.

Thanks for the reply and best regards.

-Cole Williamson
ACCP/ASNT Responsible Level III, CWI

 
 Reply 
 

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