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- since 1996 -

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Technical Discussions
Carlos Alberto
Mexico, Joined Dec 2019, 6

Carlos Alberto

Mexico,
Joined Dec 2019
6
04:29 Dec-13-2019
UT indications in a T-joint with backing bar

Hello everyone, I have a doub with signals in UT when the piece to inspect has a backing bar, sometimes its appear a small indication when the transducer is just in front to the weld and I dont be sure if its a signal producced by the backing bar or its a true flaw signal and then when I search in third leg its more stronger but in this position I think its the backing bar but the zone of the indication is the same that the small signal.
I've been rejecting those indications but the welders always say that didn't find something.
I hope someone can give me an adivice.

 
 Reply 
 
Carlos Alberto
Mexico, Joined Dec 2019, 6

Carlos Alberto

Mexico,
Joined Dec 2019
6
04:32 Dec-13-2019
Re: UT indications in a T-joint with backing bar
In Reply to Carlos Alberto at 04:29 Dec-13-2019 (Opening).

zoom image

T-joint with backing bar

This is the draw
 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 227

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
227
12:22 Dec-13-2019
Re: UT indications in a T-joint with backing bar
In Reply to Carlos Alberto at 04:29 Dec-13-2019 (Opening).

Carlos, can you do a zero degree scan from the left hand side?

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 785

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
785
04:40 Dec-15-2019
Re: UT indications in a T-joint with backing bar
In Reply to Carlos Alberto at 04:29 Dec-13-2019 (Opening).

Use 70 deg 2 MHz, and reject in first position only.
You have to be sure when you reject

 
 Reply 
 
Angel
Angel
19:24 Dec-15-2019
Re: UT indications in a T-joint with backing bar
In Reply to Carlos Alberto at 04:29 Dec-13-2019 (Opening).

At the beginning I will point out that I say this as a student.
The first step is do what Paul asks for... if it is possible.
Then I would use the tandem technique with focus on indication.
Next I would chang angle of tranducer, if the indication exist some signal would appear.
My way of thinking is correct? This is a lecture for me

 
 Reply 
 
Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 423

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
423
01:09 Dec-16-2019
Re: UT indications in a T-joint with backing bar
In Reply to Carlos Alberto at 04:29 Dec-13-2019 (Opening).

Carlos,welders are not our judges!
To verify on site the presence of an indication YOU must ‘guide’ with UT the excavation.
The probe is ‘non-descavation’ side and the highlighting of the indication with PT or MT must be performed with help of another inspector ndt. If this is not practicable, cut the weld across until depth of the indication and make MT-PT, then highlight the trace in the direction of the weld axis. If nothing of the above is practicable and the excavation is done directly in the direction of the weld axis, the chances of error increase and all the more reason you must be present. Other more expensive infallible methods (sampling, mechanical cutting, etc.).
Why you work in third leg: it's already so hard to make leg I and II ...
What can you do in leg III instead of in leg I or II ?
To make judgments about your indication you should give information for angle end also for path, distance from not-beveled part. I have indicated in yellow possible sources of geometric indications and in red bevel variations that you can expect.
greetings
mario

 
 Reply 
 
Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 423

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
423
01:13 Dec-16-2019
Re: UT indications in a T-joint with backing bar
In Reply to Mario Talarico at 01:09 Dec-16-2019 .

zoom image

carlos t.joint

carlos,
this the image
 
 Reply 
 
Carlos Alberto
Mexico, Joined Dec 2019, 6

Carlos Alberto

Mexico,
Joined Dec 2019
6
09:21 Dec-16-2019
Re: UT indications in a T-joint with backing bar
In Reply to Mario Talarico at 01:09 Dec-16-2019 .

Hi Mario, I know that the welders arent our judges and I've been being present many times wearing a welding helmet when they remove all the weld even deeper than I told them with the carbon arc gouging and I couldn't see something either and that is the reason why I have doubts if it can be a backing bar signal or a true flaw but I haven't tried performed MT, Im going to that next time.

With this type of configuration I cant work in first leg and the indication thats appears is in second leg but in that position I cant maximine the signal to determine the deep and the severity.

Greetings

 
 Reply 
 
Carlos Alberto
Mexico, Joined Dec 2019, 6

Carlos Alberto

Mexico,
Joined Dec 2019
6
09:27 Dec-16-2019
Re: UT indications in a T-joint with backing bar
In Reply to Paul Holloway at 12:22 Dec-13-2019 .

Hi Paul, unfortunately I cant do a zero degree scan because there are another accesories in the left hand side.

 
 Reply 
 
Carlos Alberto
Mexico, Joined Dec 2019, 6

Carlos Alberto

Mexico,
Joined Dec 2019
6
09:37 Dec-16-2019
Re: UT indications in a T-joint with backing bar
In Reply to Anmol Birring at 04:40 Dec-15-2019 .

Thank you Anmol for your advice, I saw your videos on YouTube maybe you should make a video one day about a topic like this.

Greetings!

 
 Reply 
 
Carlos Alberto
Mexico, Joined Dec 2019, 6

Carlos Alberto

Mexico,
Joined Dec 2019
6
09:52 Dec-16-2019
Re: UT indications in a T-joint with backing bar
In Reply to Mario Talarico at 01:13 Dec-16-2019 .

zoom image



Mario, I made another drawing, Im going to check others factors
 
 Reply 
 
Ali
NDT Inspector,
Iran, Joined Mar 2013, 109

Ali

NDT Inspector,
Iran,
Joined Mar 2013
109
12:32 Dec-16-2019
Re: UT indications in a T-joint with backing bar
In Reply to Carlos Alberto at 09:52 Dec-16-2019 .

zoom image



Carlos,
I made this sketch according to your information .may be the indications that you got, are coming from edge of backing strip plate(just assume the root gap was wider than your sketch and ultrasonic beam has beam spread instead of single line) . Also you have to perform visual inspection before welding to see real bevel configuration .also there are some point that you should be aware :
1-as you know backing strip is used just to keep the root pass to achieve good quality and backing strip usually no need to full penetrations weld (just tack welds).
2-when we used backing strip for welding the root gap has wide range up to 10mm according to AWS D1-1.( Or will little more during fabrication).
 
 Reply 
 
Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 423

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
423
01:57 Dec-17-2019
Re: UT indications in a T-joint with backing bar
In Reply to Carlos Alberto at 04:29 Dec-13-2019 (Opening).

zoom image

carlos t.joint cases

Carlos,
good that you have added information to understand the configuration, different from what was assumed in my previous post. I assumed that the not-beved thickness is equal to 3 ¾ ". Unfortunately, without the UT path of the indication the discussion is too complicated.

I too threw myself on the graph paper like Ali. In fig.1, three hypotheses of bevels: wide, medium, normal, also depends on the weld process. I mapped 4 points with distances from the not-beveled part, 6, 10,15,20 mm. In figures 2,3,4 the root configuration, after weld. In all the figures I highlighted probe position 1.9 “, to understand the evolution of geometry for beam 72°.

The config A, Fig.2, wider bevel, is similar to that of Alì. It is the one that could best fit the geometry and root in leg I. You need a bevel between 15 and 20 mm in root.
In Figs, 3.4, the bevel narrows. In fig, 3 the probe pos 1.9 " does not impact the geometry in leg I, if not in a marginal part. To the left of the probe pos. 1.9 “, depending on the index probe, a leg III scan may be necessary to see the geometry and the root, these paths may be confused with the rebond.

In fig. 4 the geometry could be hidden.

The width of the outer weld cap can change everything said (this variable is constant in our post). The same for plate-support distance (in our case also left constant) and support form (beveled or not).

Therefore, as further unfavorable condition, you will have none check points for the indications as an alternative to the main scan !!!

Too many variables in play! I don't envy you: if the whole is not well addressed from the beginning the error of the UT inspector at every step is a realistic hypothesis.
I wish you all good,
greetings
Mario
1
 
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