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Technical Discussions
Steve Mawle
Steve Mawle
05:51 Jan-08-2001
UT probe indexing

When indexing a 60 deg Al probe on a Al IIW block I get
different index point on my transducer when calibrating for 2"
of beam travel vs 4".
Any insight into this would be appreciated.
Steve Mawle



    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1219

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1219
06:33 Jan-08-2001
Re: UT probe indexing
Steve:
The acoustic velocity of Aluminium is about 3130m/s which is not so different from Steel at about 3250m/s.
I recall, many years ago, setting up for my certification exam where I was given a nominal 60 degree probe (for steel) and given an Aluminium IIW block to calibrate on.
The first thing I did was to check the angle and exit point of my probe to find how much angle difference there was from the indicated angle.
This exercise was MOST exasperating. I found that my exit point was actually OUTSIDE of the probe. It was a few years before this "banana shaped" beam was explainable for me.
Aluminium can have a pronounced crystal structure. This can provide significant anisotropy which in effect does bend the beam.

The people in Panametrics came up with a solution to make an Aluminium IIW block that tried to minimise the anisotropy effects.

But this points to a further problem. The calibration block is supposed to provide an indication of the beam characteristics in the test piece (as well as proving a method to assess the beam qualities).
Elaborate methods to produce a good quality calibration block for beam assessments may be OK for beam assessment but this no longer reflects what is hapening in the test piece.
If anisotropy effects are eliminated in the calibration block but not in the test piece you are still going to have a problem setting up a time base or predicting WHERE in the test piece signals are originating from.
Ed


: When indexing a 60 deg Al probe on a Al IIW block I get
: different index point on my transducer when calibrating for 2"
: of beam travel vs 4".
: Any insight into this would be appreciated.
: Steve Mawle




    
 
 
Alvin Dunsmorstein
Alvin Dunsmorstein
00:37 Jan-08-2001
Re: UT probe indexing
Ed, I am not sure what you are getting at here,
do you mean that because of the anisotropy effect
of the IIW Al block that the index point of the
60 Deg probe will vary when indexed at the two inch
to four inch on the same IIW block.


: Steve:
: The acoustic velocity of Aluminium is about 3130m/s which is not so different from Steel at about 3250m/s.
: I recall, many years ago, setting up for my certification exam where I was given a nominal 60 degree probe (for steel) and given an Aluminium IIW block to calibrate on.
: The first thing I did was to check the angle and exit point of my probe to find how much angle difference there was from the indicated angle.
: This exercise was MOST exasperating. I found that my exit point was actually OUTSIDE of the probe. It was a few years before this "banana shaped" beam was explainable for me.
: Aluminium can have a pronounced crystal structure. This can provide significant anisotropy which in effect does bend the beam.

: The people in Panametrics came up with a solution to make an Aluminium IIW block that tried to minimise the anisotropy effects.

: But this points to a further problem. The calibration block is supposed to provide an indication of the beam characteristics in the test piece (as well as proving a method to assess the beam qualities).
: Elaborate methods to produce a good quality calibration block for beam assessments may be OK for beam assessment but this no longer reflects what is hapening in the test piece.
: If anisotropy effects are eliminated in the calibration block but not in the test piece you are still going to have a problem setting up a time base or predicting WHERE in the test piece signals are originating from.
: Ed

:
: : When indexing a 60 deg Al probe on a Al IIW block I get
: : different index point on my transducer when calibrating for 2"
: : of beam travel vs 4".
: : Any insight into this would be appreciated.
: : Steve Mawle




    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1219

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1219
03:11 Jan-09-2001
Re: UT probe indexing
Alvin:
The 2inch and 4inch radii on an IIW block are not items I have ever used. The Original IIW block had only a 100mm radius from which to assess the exit point (and set range).
It is more commonly referred to as the A2 (or in the UK the V1) block (see BS-2704). It has a 0.5mm x 4mm deep x 30mm long slot on both sides at the index reference point.
However, the principles would be the same.
When placing the probe on the block facing the radius, you maximise the radius' signal and assume that the sound has travelled a straight line from the centre point of the radiused portion.
The point of the probe over the IIW block index point is assumed to indicate the exit point of the probe. But on the block I was given to use the signal I managed to maximise required that the probe be pushed closer towards the 100mm radius until the back edge of the probe was over the index point.
Since I did not have the US modified version of the original IIW block I had only one radius to maximise so I cannot state the index point of the 60 degree probe will vary when indexed at the two inch to four inch on the same IIW block.
This experience was offered as an explanation to Steve's observation.

: Ed, I am not sure what you are getting at here,
: do you mean that because of the anisotropy effect
: of the IIW Al block that the index point of the
: 60 Deg probe will vary when indexed at the two inch
: to four inch on the same IIW block.

:
: : Steve:
: : The acoustic velocity of Aluminium is about 3130m/s which is not so different from Steel at about 3250m/s.
: : I recall, many years ago, setting up for my certification exam where I was given a nominal 60 degree probe (for steel) and given an Aluminium IIW block to calibrate on.
: : The first thing I did was to check the angle and exit point of my probe to find how much angle difference there was from the indicated angle.
: : This exercise was MOST exasperating. I found that my exit point was actually OUTSIDE of the probe. It was a few years before this "banana shaped" beam was explainable for me.
: : Aluminium can have a pronounced crystal structure. This can provide significant anisotropy which in effect does bend the beam.

: : The people in Panametrics came up with a solution to make an Aluminium IIW block that tried to minimise the anisotropy effects.

: : But this points to a further problem. The calibration block is supposed to provide an indication of the beam characteristics in the test piece (as well as proving a method to assess the beam qualities).
: : Elaborate methods to produce a good quality calibration block for beam assessments may be OK for beam assessment but this no longer reflects what is hapening in the test piece.
: : If anisotropy effects are eliminated in the calibration block but not in the test piece you are still going to have a problem setting up a time base or predicting WHERE in the test piece signals are originating from.
: : Ed

: :
: : : When indexing a 60 deg Al probe on a Al IIW block I get
: : : different index point on my transducer when calibrating for 2"
: : : of beam travel vs 4".
: : : Any insight into this would be appreciated.
: : : Steve Mawle




    
 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 174

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
174
02:21 Jan-12-2001
Re: UT probe indexing
waves at a plastics wedge/metal boundary above the first critical angle, i.e. there is also a wave mode conversion.

- Even when always using the same probe wedge the mode conversion (of elastic waves) will be different if the elastic properties of the calibration block change, so it makes a big difference if you use steel or titanium or aluminium.

- The determination of the index point and the beam angle on a calibration block is based on a simple ray model:
A plane wave bounces onto a boundary between two materials of quite different acoustical impedances (i.e. the source has to be far away from the boundary) and by refraction a plane wave front is generated in the second material.

- But in practice in most cases the boundary is not in the far field but in the near field, therefore no plane wave front hits the boundary, there are pressure and phase fluctuations at the boundary, which influence the generation of the mode converted waves in the second material depending on the elastic constants of this material.

- When only looking for the maximum signal in the calibration block, therefore, the index point of a common angle beam probe usually shifts when changing the material of the calibration block.

- Additional to that, it is difficult to measure the angle of the direction of sound propagation at shorter distances. The longer the distance to a reflector the more precise the beam angle measurement.

- To get the beam direction by looking for the maximum echo amplitude only it is necessary to measure at distances where the probe has a defined main lobe. For single transducer probes this means the reflector has to be in the far field. For focusing probes or dual-element-probes this measurement is only possible if the reflector is in the focal area.

- The purpose of the IIW calibration block (see the titles of the standards) is only to check the probe parameters during weld testing (influence of wear).

- These blocks are not suited to give precise measurements of beam angle and index point asit ist needed e.g. during manufacturing control. The block width (25 mm) is to small and for some frequencies and transducer sizes the radius is to small to give undisturbed far-field conditions.

Kind regards

Udo Schlengermann


: When indexing a 60 deg Al probe on a Al IIW block I get
: different index point on my transducer when calibrating for 2"
: of beam travel vs 4".
: Any insight into this would be appreciated.
: Steve Mawle




    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1219

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1219
05:20 Jan-17-2001
Re: UT probe indexing
As a follow-up to your querry I would direct you attention to a paper;
"Ultrasonic Testing of Anisotropic Media, False Indications and the Cause of Their Occurence"; by M.Brissaud & H.Kleimann, published Conference Proceedings for Ultrasonics International 83, Halifax, Canada 12-14 July 1983, Butterworth Scientific Limited.
In this paper (page 459) the explanation of the difference between the apparent and actual angles are provided as the source of a variable exit point in the same block.

(My thanks to Dr. Fred Hotchkiss for bringing this paper to my attention.)

Ed


: Ed, I am not sure what you are getting at here,
: do you mean that because of the anisotropy effect
: of the IIW Al block that the index point of the
: 60 Deg probe will vary when indexed at the two inch
: to four inch on the same IIW block.

:
: : Steve:
: : The acoustic velocity of Aluminium is about 3130m/s which is not so different from Steel at about 3250m/s.
: : I recall, many years ago, setting up for my certification exam where I was given a nominal 60 degree probe (for steel) and given an Aluminium IIW block to calibrate on.
: : The first thing I did was to check the angle and exit point of my probe to find how much angle difference there was from the indicated angle.
: : This exercise was MOST exasperating. I found that my exit point was actually OUTSIDE of the probe. It was a few years before this "banana shaped" beam was explainable for me.
: : Aluminium can have a pronounced crystal structure. This can provide significant anisotropy which in effect does bend the beam.

: : The people in Panametrics came up with a solution to make an Aluminium IIW block that tried to minimise the anisotropy effects.

: : But this points to a further problem. The calibration block is supposed to provide an indication of the beam characteristics in the test piece (as well as proving a method to assess the beam qualities).
: : Elaborate methods to produce a good quality calibration block for beam assessments may be OK for beam assessment but this no longer reflects what is hapening in the test piece.
: : If anisotropy effects are eliminated in the calibration block but not in the test piece you are still going to have a problem setting up a time base or predicting WHERE in the test piece signals are originating from.
: : Ed

: :
: : : When indexing a 60 deg Al probe on a Al IIW block I get
: : : different index point on my transducer when calibrating for 2"
: : : of beam travel vs 4".
: : : Any insight into this would be appreciated.
: : : Steve Mawle




    
 
 

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