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- since 1996 -
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Terry White
Terry White
07:05 Feb-29-2008
Curvature of cylinders and UT

At what point does the curvature of a cylindrical object lose importance for comparison to the curvature of a reference standard? At some point it seems that the curvature of a larger diameter cylinder becomes almost flat in respect to a focused ultrasonic longitudinal wave sound beam. In some cases, I know that flat reference strandards are allowed to be used when testing cylindrical objects over a certain diameter. How is this determined? It is often expressed that a reference standard should be within 10% diameter of the material being tested or .500" or 1.00", whichever is less.


    
 
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Dent
Consultant, NDE Manager NDELevel III/3
NDT Consultant, Canada, Joined Nov 1998, 248

Dent

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
248
03:37 Mar-03-2008
Re: Curvature of cylinders and UT
----------- Start Original Message -----------
Different rules for different specs.
Some say 20" is the point where you can use a flat block.
Some say under 100" you add certain # of Db.
Also depends on size of probe.

As you see no simple answer.


: At what point does the curvature of a cylindrical object lose importance for comparison to the curvature of a reference standard? At some point it seems that the curvature of a larger diameter cylinder becomes almost flat in respect to a focused ultrasonic longitudinal wave sound beam. In some cases, I know that flat reference strandards are allowed to be used when testing cylindrical objects over a certain diameter. How is this determined? It is often expressed that a reference standard should be within 10% diameter of the material being tested or .500" or 1.00", whichever is less.
------------ End Original Message ------------




    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1268

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1268
02:50 Mar-03-2008
Re: Curvature of cylinders and UT
Terry;
As Dent pointed out, there are different rules and your access to options may be dictated by these rules.

ASME has one set of rules for pipe and another for plate. For pipe you MUST use a calibration block of the same size and schedule as being tested.
For curved Plate, the curvature of calibration block is to be within 0.9-1.5 times the curvature tested up to 20 inch diameter and for over 20 inch diameter the calibration block may be flat.
But ASME is not very practical in that no consideration is made for the relative area of effective contact. A smaller probe will better couple to a smaller diameter than a larger area probe.

EN-1714 is much better in this regard. They require that the gap between the test surface and the bottom of the probe shoe not be greater than 0.5mm. If the condition cannot be met then the probe shoe requires shaping to adapt to the curvature.

EN-583-2 describes a transfer value method (a limit of 6dB transfer value is allowed).

All of these "options" I interpret to mean to apply to a probe being used on the convex test surface. When testing from the inside (concave) surface the probability of a flat probe being effective is low. I would expect that a lot of care would be needed to ensure that the curvature of the calibration piece and the probe shoe are well matched to the test surface for inspection from the Concave surface.
Ed

----------- Start Original Message -----------
: Different rules for different specs.
: Some say 20" is the point where you can use a flat block.
: Some say under 100" you add certain # of Db.
: Also depends on size of probe.
: As you see no simple answer.
:
: : At what point does the curvature of a cylindrical object lose importance for comparison to the curvature of a reference standard? At some point it seems that the curvature of a larger diameter cylinder becomes almost flat in respect to a focused ultrasonic longitudinal wave sound beam. In some cases, I know that flat reference strandards are allowed to be used when testing cylindrical objects over a certain diameter. How is this determined? It is often expressed that a reference standard should be within 10% diameter of the material being tested or .500" or 1.00", whichever is less.
------------ End Original Message ------------




    
 
 Reply 
 
S.Senthilkumar
Engineering, QA/QC/NDT
NOV (National Oilwell Varco), Angola, Joined Mar 2006, 41

S.Senthilkumar

Engineering, QA/QC/NDT
NOV (National Oilwell Varco),
Angola,
Joined Mar 2006
41
06:28 Mar-04-2008
Re: Curvature of cylinders and UT
Yes, Variation will be there.
Testing to be done as per your specification and standards using for the testing. Practically Flat object cannot compromise with any curved surface. You have to do curvature correction and determine the real beam path. Minimum to Maximum will occur when diameter keeps on decreasing.
----------- Start Original Message -----------
: Different rules for different specs.
: Some say 20" is the point where you can use a flat block.
: Some say under 100" you add certain # of Db.
: Also depends on size of probe.
: As you see no simple answer.
:
: : At what point does the curvature of a cylindrical object lose importance for comparison to the curvature of a reference standard? At some point it seems that the curvature of a larger diameter cylinder becomes almost flat in respect to a focused ultrasonic longitudinal wave sound beam. In some cases, I know that flat reference strandards are allowed to be used when testing cylindrical objects over a certain diameter. How is this determined? It is often expressed that a reference standard should be within 10% diameter of the material being tested or .500" or 1.00", whichever is less.
------------ End Original Message ------------




    
 
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