where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -
1574 views
Technical Discussions
David Bunch
David Bunch
23:52 Feb-01-2010
Plotting ID indications

If the base of a crack or a notch is the main reflector in a piece of steel, is it possible to accurately plot the through-wall thickness of it using the 3-point 6 dB drop method?

I practiced plotting some notches simulating lack of fusion on a weld today. They were very shallow, and my plotting simply plotted the beam spread. But I could tell they were ID connected and what their widths were. However, when I attempted to plot a .100" deep ID notch in the edge of the block, the plotting continuously came out wrong. It was showing a square notch to be C shaped. The main plotting angle (70 degrees) was at the end of the first leg (so it was obviously ID connected). Moving in and dropping the signal amplitude by half, the next plotting angle (64 degrees) registered a depth of .850", where as it should have read .900" (since it was a .100" deep notch in a 1" block). Pulling back to my third plotting angle (76 degrees), it vastly oversized the notch and put its maximum depth at .750".

Is this simply the various angles registering off the same reflection point, and not truely plotting the defect?

    
 
 Reply 
 
Collin Maloney
NDT Inspector, - Plant Inspector
Applus RTD, Australia, Joined Nov 2000, 147

Collin Maloney

NDT Inspector, - Plant Inspector
Applus RTD,
Australia,
Joined Nov 2000
147
23:48 Feb-02-2010
Re: Plotting ID indications
In Reply to David Bunch at 23:52 Feb-01-2010 (Opening).

David, it sounds as though you are doing just that. Have you been using a beam profile and plot of the block?, if so, you should be able to simulate and identify what is happening to the sound beam and not guess.

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

andrew.cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
01:39 Feb-03-2010
Re: Plotting ID indications
In Reply to David Bunch at 23:52 Feb-01-2010 (Opening).

Download Virus Scan recommended!

Download

Hi David
Trying to size and depth an ID connected reflector (as you have found out) can have many problems: mainly from the acoustics of the internal reflecting surfaces. This is due to the sound reflecting back from a corner at half the internal angle ***please see diagram in attached document*** for example, you will find that a 90° notch (or corner) will reflect an acoustically enhanced (amplified) wave at 45° - a.k.a. ``The Corner Trap``. This causes the dB drop methods to oversize the reflector(s).
Probe selection is important.
Because of this `corner trap` NEVER use a 60° on an ID connected reflector. To demonstrate how misleading this is try and depth the bottom corner from the side of an I.I.W. V1. The I.I.W. V1 has a thickness of 1.0`` (or, 25mm) so simple trigonometry would put the maximized bottom reflector at a 2.0`` (50mm) sound path. In reality, the reflector maximizes on the screen appears at approximately 1.6`` (42mm) sound path. ***please see diagram in attached document***
(Though the older style Panametrics probes did not have this problem because of their unique design)
This phenomenon is less evident (though still there)with a 70°, but using the trailing edge at 64° (as you were) has picked up the corner trap.
Using a 45° will work with a corner trap, but in the real world cracks are not all at 90° (and the material thickness may not allow for a 45° probe), so there will always be a margin of error.
I would prefer to use Max. Amp. for the cross – for both sectional and depth sizing.
For further interest, please note that the attached diagram also demonstrates how a 90° corner trap responds to a 30° probe. This will introduce you to another school of thought in the creeping wave debate. It is my belief that if one takes a little time to understand how a corner trap amplify reflections (simple acoustics) he (or she) will be in a much better position to understand the true properties of the so-called creeping wave.
Please find 2 attachments that I am putting together for this topic.
The Max. Amp., attachment is Not a Final draft and I encourage your feedback. Please respect all Copyrights.
    
 
 Reply 
 
David Bunch
David Bunch
13:36 Feb-03-2010
Re: Plotting ID indications
In Reply to andrew.cunningham at 01:39 Feb-03-2010 .

Wow, excellent reply Andrew. Thank you for the files.

Colin, yes I have plotted the the beam profiles on pen and paper. I continuously got a concave or convex beam profile on a vertical corner.

Andrew, I'm excited to try your Max Amp method. Again, I very much appreciate the information you just provided me.

    
 
 Reply 
 
David Bunch
David Bunch
01:38 Feb-08-2010
Re: Plotting ID indications
In Reply to David Bunch at 13:36 Feb-03-2010 .

I experimented with my plotting again. I used a 70 degree, .25" 5mhz probe to plot lack of penetration in a 1 inch weld. The 70 degree beam and 76 degree beam plotted correctly, but the 66 degree beam did not. Though it should have plotted in the first leg, there was too much sound path. So I disregarded that angle and only plotted the 70 and 76 degree beams. It plotted vertically, on the appropriate side of the weld. It did oversize the throughwall depth of the flaw, but not by much. This can be attributed to beam spread. Length sizing of the flaw was accurate.

I didnt have time, but I would like to try this two-point plotting method on a ID connected flaw that is larger than my beam spread, such as the 10% notch in my 1" pipe. Hypothetically it should work, as it avoids the creeping-wave error.

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

Andrew Cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
02:33 Feb-10-2010
Re: Plotting ID indications
In Reply to David Bunch at 01:38 Feb-08-2010 .

Download Virus Scan recommended!

This might help! Please see the attachment.
    
 
 Reply 
 

Product Spotlight

High-end Ultrasonic Flaw Detector with 32:128PR PAUT and 2-ch TOFD: SyncScan 2

SIUI’s newly launched SyncScan 2, is a high-end ultrasonic flaw detector with 32:128PR PAUT and
...
2-ch TOFD, which can maximize your efficiency for PA and TOFD. ● Support PA/TOFD/UT ● 32-ch PA is more suitable for inspection on extra-thick wall and high-attenuation material. ● 32-ch PA and 2-ch TOFD work simultaneously. ● Support PR mode for corrosion inspection.
>

IRIS 9000Plus - Introducing the next generation of heat exchanger inspection.

Representing the seventh generation of the IRIS system, the IRIS 9000 Plus has nearly 200 years of c
...
ombined field inspection experience incorporated in its design. This experience combined with a strong commitment to quality and a history of innovation has made Iris Inspection Services® the undisputed leader in IRIS technology.
>

Combination of Digital Image Correlation and Thermographic Measurements

The combination of measuring results from the digital image correlation (ARAMIS, DIC) and temperat
...
ure measuring data from infrared cameras permits the simultaneous analysis of the thermal and mechanical behavior of test specimens in the materials and components testing field.
>

Lyft™: Pulsed Eddy Current Reinvented

PEC Reinvented—CUI Programs Redefined Corrosion under insulation (CUI) is possibly the greatest u
...
nresolved asset integrity problem in the industry. Current methods for measuring wall thickness with liftoff, without removing insulation, all have severe limitations. Eddyfi introduces Lyft — a reinvented, high-performance pulsed eddy current (PEC) solution. The patent- pending system features a state-of-the-art portable instrument, real- time C-scan imaging, fast data acquisition with grid-mapping and dynamic scanning modes, and flexibility with long cables. It can also scan through thick metal and insulation, as well as aluminum, stainless steel, and galvanized steel weather jackets. Who else but Eddyfi to reinvent an eddy current technique and redefine CUI programs. Got Lyft?
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window