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Technical Discussions
Illdan
Illdan
11:41 Jan-24-2013
UT 60º geometrical problem

Hi!

I have a problem that i was wondering if anyone could help me with.

A couple of days ago i did UT on a bridge, two 16mm plates welded togheter (V-Joint, 25-30º angle)
It was a little misalignement (1-2mm).

When i used the 60º i got an indication echo on a depth of 8mm, pretty much all along the weld, from one side of the joint.

We grinded the weld at several places and found that there was nothing wrong, some geometrical problem must have made the indication echo start?! If i didn't know any better i would have guessed it was a lack of fus (high, sharp echo, DAC+4dB)

Does anyone know what made this echo occur? I'm pretty new at UT and really want to know why this things happen. some more info

Soundpath from indication 50mm
- " - from probe 30 mm

    
 
 Reply 
 
creed
NDT Inspector,
n.n., Joined Jul 2009, 24

creed

NDT Inspector,
n.n.,
Joined Jul 2009
24
11:53 Jan-24-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 11:41 Jan-24-2013 (Opening).

Hi there,
It hard to explain your things happened with given information. But you should aware that if the defect is lack of fusion it will be hard to detect by visual after cut out the weld. Did you do MPI right after grinding, it is sensitive to lack of fusion evident inside the cut weld. That is my opinion.
Cheers.

    
 
 Reply 
 
mark
mark
12:06 Jan-24-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 11:41 Jan-24-2013 (Opening).

Dear Illdan,
did you do MPI or DPI after grinding?
Often you cant find LOF visualy.

    
 
 Reply 
 
Illdan
Illdan
12:21 Jan-24-2013
Re: UT 60º geometrical problem
In Reply to mark at 12:06 Jan-24-2013 .

I did, MPI after grinding, yes, didn't find anything. Altough i think you pretty often can see the LOF after grinding, the welders also used a blowtorch (is that the right word?) and they couldnt see anything when opening with that either.

    
 
 Reply 
 
creed
NDT Inspector,
n.n., Joined Jul 2009, 24

creed

NDT Inspector,
n.n.,
Joined Jul 2009
24
12:35 Jan-24-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 12:21 Jan-24-2013 .

Hi,
So the thing you need to do now is calculating shear wave beam profile with exactly prep of the weld, build up the sketch of probe position vs prep of weld and and the measurement of beam profile. If everything is correctly and very sure, you could be confident to say they are defects. Remember NDT is an interpretation not 100% for sure. If possible you can try to do RT to confirm.

    
 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
15:29 Jan-24-2013
Re: UT 60º geometrical problem
In Reply to creed at 12:35 Jan-24-2013 .

Calling a repair on an indication from one probe, one direction is dangerous. Especially a 60 degree. You dont mention stand-off distance.

Confirmation of presence of a defect should be possible and is needed from a different direction or with a different angle.

Unless you work with focussed probes, beam spread is broad and reflections from geometry with the lower angle emissions of your beam spread can lead to techs calling unnecessary repairs.

1    
 
 Reply 
 
Cole
Cole
15:58 Jan-24-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 11:41 Jan-24-2013 (Opening).

Hello,

I first have to tell you that like stated above a tech should always be very cautious when calling a defect when you can only verify the location from one side of the weld. Secondly, I am fairly confident that what you are seeing is a mode converted signal that is reflecting off of the cap of your weld. I have seen this happen many times when using a 60 deg shearwave. Most of the time this signal if mapped out using your surface distance calculation will map outside of the weld cap; however, not always. My recommendation would go back to mapping out your indication on a weld profile drawing, from both sides of the weld. Typically defect classification is 90% flaw location and 10% signal analysis. Hope this helps.

    
 
 Reply 
 
Jon Wallis
NDT Inspector, -
Netherlands, Joined Feb 2010, 626

Jon Wallis

NDT Inspector, -
Netherlands,
Joined Feb 2010
626
17:20 Jan-24-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 11:41 Jan-24-2013 (Opening).

You found this indication at full skip so several possibilities apart from the ones already mentioned come to mind.
Did you rely on the flaw detector to tell you depth? Many techs make mistakes by blindly relying on the electronics especially on full skip. Make a scale drawing of the weld and plot the echo with a good old fashioned sharp pencil, ruler and protractor. This will show you whether your echo is reflecting from the parallel opposite surface or maybe mode converting.
Are you sure it was a 60 degree probe? 50mm beam path with 16mm wall thickness is approximately full skip to the surface with a 45 degree probe.
Did you examine from the other face to try and find the indication at half skip? This confirmation is one way of doing the check that Nigel suggested.
If you find an indication at full skip and cannot confirm it with another angle or by scanning from another face, before calling a repair you can ask for the cap to be removed at one or two positions and look for the indication at half skip from the opposing face. If you conclude that the echo was from the geometry, no unnecessary repair will have been made.

1    
 
 Reply 
 
Illdan
Illdan
09:12 Jan-25-2013
Re: UT 60º geometrical problem
In Reply to Jon Wallis at 17:20 Jan-24-2013 .

Thanks for all your answers! Since i'm the only one performing UT in my company it's good to have place where you can ask more seasoned operators.

I didn't find the indication with any other angle, tried both 45 and 70, that's what caught my suspicion, also only one face of the weld was accessible. yes i'm sure it was a 60 degree.

Sorry Nigel, i don't know what stand-off distance means, tried to find the swedish word for it but with no luck :)

    
 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
10:06 Jan-25-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 09:12 Jan-25-2013 .

Illdan

Stand off distance (SOD) is the trigonemetric calculation based on the refracted angle (eg 60 degrees) and the displayed beam path. So it is the distance from the sound emission point of your probe to directly above the reflection point. If the SOD measures to a point outside the weld cap/HAZ then its one indication that the signal may be spurious, eg mode conversion.

Hope this is understandable, if not consult any UT textbook

    
 
 Reply 
 
Illdan
Illdan
10:20 Jan-25-2013
Re: UT 60º geometrical problem
In Reply to Nigel Armstrong at 10:06 Jan-25-2013 .

Ah! then i know what you mean! it was 30mm (with x-point 14mm) i wrote that in the first message " from probe 30 mm"

    
 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
12:00 Jan-25-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 10:20 Jan-25-2013 .

Go back to SOHCAHTOA trig mnemonic.

16mm thick, 60 degree probe 1/2 skip distance BP = 32mm, SOD = 27mm approx
Full skip distance BP = 64mm, SOD = 54mm approx.

50 mm BP for 60 degree probe calculates to approx 43mm SOD, how have you arrived at 30mm?

The math doesnt lie! If it doesnt plot out in the weld then 95% of the time it isnt in the weld The other 4% your using the wrong data (mistaken probe angle, wrong factors). Allowance of 1% for strange contributing factors.

    
 
 Reply 
 
Illdan
Illdan
12:32 Jan-25-2013
Re: UT 60º geometrical problem
In Reply to Nigel Armstrong at 12:00 Jan-25-2013 .

Forgot to tell you that it was welded with a root support - 5mm thick, might that have something to do with the data recieved?

    
 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
12:44 Jan-25-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 12:32 Jan-25-2013 .

Thats a possibility if the backing strip is still attached!

100 % description of an inspection problem is challenging!

    
 
 Reply 
 
Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 411

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
411
16:14 Jan-27-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 12:32 Jan-25-2013 .

zoom image
Illdan,
the signal from the bottom of the backing strip attached is a possibility. Another possibility is the shear wave reflection from the outer cap, after simple reflection in root: this is compatible with the sound path observed: 32 (half skip path) + 16 (vertical thickness path) = 48 + external cap misaleneament + root = misaleneament approximately 52.
Longitudinal mode conversion, instead, require external cap excessively large and minor path as result of the speed change .
Is to be noted that each of these possibilities requires the same probe position and it is an operating error to be corrected: with incidence in root is a big hazard to perform the examination in reflection on the body welding
Greetings
    
 
 Reply 
 
massimo carminati
Consultant, AUT specialist
IMG Ultrasuoni Srl, Italy, Joined Apr 2007, 691

massimo carminati

Consultant, AUT specialist
IMG Ultrasuoni Srl,
Italy,
Joined Apr 2007
691
17:01 Jan-27-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 11:41 Jan-24-2013 (Opening).

What you described is normally a reflection from the root to the cap, and this happens particularly with the 60°. Normally, seen from top, this false call lies few mm outside the weld on the base material opposite side from inspection,

1    
 
 Reply 
 
Illdan
Illdan
08:09 Jan-29-2013
Re: UT 60º geometrical problem
In Reply to massimo carminati at 17:01 Jan-27-2013 .

Thanks so much for all your help! It helped alot!
Does anyone have a tip for a good software to make sketches of welds and draw up ultrasonic beam pats and so on the computer?

    
 
 Reply 
 
James Scalf
NDT Inspector,
Royal Canadian Air Force, Canada, Joined Oct 2012, 273

James Scalf

NDT Inspector,
Royal Canadian Air Force,
Canada,
Joined Oct 2012
273
13:36 Jan-29-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 08:09 Jan-29-2013 .

Illdan,

Eclipse Scientific makes a program called the ESBeam tool which is quite good. It runs CAD, can do 3-D imaging and shows just about everything you may need to see about your sound path. There are other programs as well but from what I have read (I have not used the software yet but have ordered it) the ESBeam tool is the most recommended.

    
 
 Reply 
 
Mokshda
Mokshda
10:22 Aug-22-2013
Re: UT 60º geometrical problem
In Reply to massimo carminati at 17:01 Jan-27-2013 .

What method would you use to differentiate between an actual root indication and a reflection from the root gap? I am very new to NDT and I don't know the limitations of the different methods yet.

Thank you.

    
 
 Reply 
 
Jon Wallis
NDT Inspector, -
Netherlands, Joined Feb 2010, 626

Jon Wallis

NDT Inspector, -
Netherlands,
Joined Feb 2010
626
12:50 Aug-22-2013
Re: UT 60º geometrical problem
In Reply to Mokshda at 10:22 Aug-22-2013 .

If by root gap you mean lack of root fusion or lack of penetration, careful measurement is the way to determine the difference between a healthy root and a defective one. A root echo will appear at a specific measured distance between the index point of the probe and the centre of the weld (the stand-off distance explained by Nigel). When lorf or lop is present the measured distance will be slightly further away from the weld.
This requires accuracy with measurement of probe angle, index point, maximising your echo.
As I suggested before, make a pencil-and-paper drawing and you can 'see' what your ultrasound is reflecting from.

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

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
19:16 Aug-22-2013
Re: UT 60º geometrical problem
In Reply to Illdan at 11:41 Jan-24-2013 (Opening).

As you can see from all the confident replies, we have all made the same mistake. The skill of the technician is to learn from them and not to repeat them. All of the above statements are true as they have found from their own experience, so I’ll add to them.
1 Never trust the sound after the bounce.
2 Spay water or WD40 onto the surface to see if it affects the signal.
3 Always confirm with a 70 or another probe angle.
4 After you find a reflector, try to eliminate it, before you call it as a defect.

Other advice. There are some specs that state that the technician is to use only use one probe (70) when the thickness is less than 25.4 mm and to reject by amplitude. In my opinion. The spec tries to tie the hands of the technician and takes no responsibility for their nations bridges falling down.

When I was writing my book, I was chatted to an engineer about the title, we discussed how the knowledge was obtained. He came up with a title “30 years of F**K UP’s.”

All I’m saying is, you have made one of the most common mistakes in UT. You have now learned and won’t do it again. We are all on a learning curve.

All the best

    
 
 Reply 
 
soumya halder
soumya halder
17:07 Jun-15-2015
Re: UT 60º geometrical problem
In Reply to Illdan at 11:41 Jan-24-2013 (Opening).

normaly 60 degree probe has the greatter modconversion problm , and it has also bettar resolution ....
sometime it will show the wrong backwall echo, bt it is no prboblm, ony u have to chake the indication echos depth and beam path. means if your indication depth 20mm in 40 mm job thekness, bempath must be 40mm, measn you have to use the formula T*sec@.

    
 
 Reply 
 
Inspector Testimony
Inspector Testimony
18:41 Jul-17-2019
Re: UT 60º geometrical problem
In Reply to andrew cunningham at 19:16 Aug-22-2013 .

i will like to know more who will help i have some questions please.

    
 
 Reply 
 
Sri Krishna Chaithanya
Sembmarine, Singapore, Joined Sep 2018, 6

Sri Krishna Chaithanya

Sembmarine,
Singapore,
Joined Sep 2018
6
06:15 Jul-22-2019
Re: UT 60º geometrical problem
In Reply to Illdan at 11:41 Jan-24-2013 (Opening).

Hi,

Have you checked if there is any mode conversion echo (gerneally reflecting from surface)

We also find in 20 mm butt weld (SAW), same type of indication, all the length found in the HAZ area. i.e it is coming from some mode conversion echo, same we grinded at that location and find nothing. We taken RT as a back up and confirmed that is a profile echo.
Out of which 3 mts... we found 100 mm roughtly the mode conversion signal is coming from surface refelction (by tapping technique we confirmed this).

Hope you can try this in future.....

Next time if you got the same problem.. try TOFD for butt welds. you can confirm the defect is real or not.

Thanks.

    
 
 Reply 
 

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