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Technical Discussions
suresh
suresh
02:54 Aug-15-2007
curved probes in ToFD

what is the criteria for choice of curved probes in TOFD?

suresh


    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1235

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1235
03:52 Aug-15-2007
Re: curved probes in ToFD
Suresh:
I am not aware of any of the existing TOFD Codes (EN, ASTM or BS) giving instruction on curvature matching of probes. The best advice I have seen is in the EN Standard for UT on Welded Joints, EN1714. There, in paragraph 6.3.3, instruction is made for Adaption of Probes to curved scanning surfaces. This requires that the gap between the test surface and bottom of the probe shoe be not greater than 0.5mm. They suggest that this is satisfied when the diameter of the component is 15 times the dimension of the probe shoe (in the direction of examination) for a flat probe....otherwise the probe SHALL be adapted to the curved surface. I assume this is for testing from the OD and not the ID.
For testing from the OD and using the 0.5mm gap as a guide I generally recommend that when the probe shoe is curved its radius should be greater than or equal to the test surface curvature (not to exceed the 0.5mm gap on the shoe edges).
Avoid making the probe shoe curvature LESS than the test part. This will result in a gap in the middle of the shoe over the test piece. Even if the gap is only 0.5mm at the middle of the shoe the amplitude loss can be between 6-12dB!!
Regards
Ed

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: what is the criteria for choice of curved probes in TOFD?
: suresh
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Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 176

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
176
05:26 Aug-15-2007
Re: curved probes in ToFD
----------- Start Original Message -----------
: what is the criteria for choice of curved probes in TOFD?
: suresh
------------ End Original Message ------------

In addition to the reply of Ed Ginzel with respect to the referenced standards:

CEN/TS 14751:2005
Use of time-of-flight diffraction technique (TOFD) for testing of welds

in 7.2.2 asks for the matching of probes according to EN 1714.

EN 1714:1997 (2002)
Ultrasonic testing of welded joints

in 6.3.3 gives the equation referenced by Ed Ginzel.

But this equation is not correct.

EN 1417 is under revision now and will be published again soon.

The correct equation (when the max gap is smaller than 0.5 mm, which can be tolerated for 4 MHz), is

Dobj < (D)squared/ 2 mm,

where Dobj is the outer diameter of the object, and D is the dimension of the transducer parallel to the curvature.

The same correction has to be made to the respective equations in 3.4.1 and 3.4.2 of

EN 583-2:2001
Ultrasonic testing - Part 2: Sensitivity and range setting

(The above equation with squared transducer diameter is correct)

Best regards

Udo Schlengermann
GE Inspection Technologies GmbH
Huerth, Germany

Chairman of CEN/TC121/SC5/WG2 (UT of welds)
Chairman of CEN/TC138/WG2 (UT)




    
 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 176

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
176
05:38 Aug-15-2007
Re: curved probes in ToFD
Correction:

Before someone starts to think about my last comment,
I have to apologize for two mistypings:

- The European Standard of course is EN 1714 (not 1417).


- The correct equation is

Dobj > (D)squared/ 2 mm

( Dobj bigger not smaller than - all dimensions in mm)

Sorry
Udo Schlengermann


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: what is the criteria for choice of curved probes in TOFD?
: suresh
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