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Technical Discussions
Syed Faran Hussain
Engineering
FFC Pakistan, Pakistan, Joined May 2005, 17

Syed Faran Hussain

Engineering
FFC Pakistan,
Pakistan,
Joined May 2005
17
00:59 Jun-15-2005
UT of Austenetic SS

UT is more easy for carbon steels as compared to Austenitic SS. WHY?


    
 
 Reply 
 
Ed T.
Ed T.
04:23 Jun-15-2005
Re: UT of Austenetic SS
----------- Start Original Message -----------
: UT is more easy for carbon steels as compared to Austenitic SS. WHY?
------------ End Original Message ------------

Yes because the Austenitic S/S has a coarse grain structure especially in the welds. The welds and HAZ show a dendritic or columnar grain structure that can redirect shear waves downwards and give you false indications.


    
 
 Reply 
 
Rich Roberts
Engineering, Executive Managment
Quest Integrity Group, USA, Joined Nov 1998, 78

Rich Roberts

Engineering, Executive Managment
Quest Integrity Group,
USA,
Joined Nov 1998
78
04:30 Jun-15-2005
Re: UT of Austenetic SS
Good Day Syed,

Yes, performing Ultrasonic (UT)inspections on Carbon Steel is much easier than Stainless Steel. Carbon steel has a smaller grain structure, hence the ultrasonic waves pass through the material much easier and the signal to noise ratio is much less. Stainless Steel on the other hand contains much larger grain structure and creates a higher signal to noise ratio. You will be able to increase overall UT transducer frequency in Carbon Steel than Stainless Steel, which inadvertently provides more resolution in the test process.

Regards, Rich Roberts


----------- Start Original Message -----------
: UT is more easy for carbon steels as compared to Austenitic SS. WHY?
------------ End Original Message ------------




    
 
 Reply 
 
Jim Knowles
Jim Knowles
02:31 Jun-16-2005
Re: UT of Austenetic SS
----------- Start Original Message -----------
: UT is more easy for carbon steels as compared to Austenitic SS. WHY?
------------ End Original Message ------------

You have to look at the material and how it was formed, for example; Carbon steel is easily tested by ultrasonics, but we always make allowances for attenuaion, this is due to the grain structure differences. Austenitc stainless steel providing it is in a wrought state is usually quite easy to test dependant on grain size and structure, therefore we may make changes in the test frequency.
When testing austenitic welds compared to carbon steel weldments the picture changes as the grain structure can alter witin a few millimetres. This is normally refred to as differences between an Isotropic and Anisotropic structure.
Wew can address these changes by modifying our transducers and move to angled longitudinal waves instead of shear waves. Compression waves we alter the frequency to accomodate.



    
 
 Reply 
 
J. Mark Davis
Teacher, And Consultant
University of Ultrasonics, Birmingham, Alabama, USA, Joined Mar 2000, 85

J. Mark Davis

Teacher, And Consultant
University of Ultrasonics, Birmingham, Alabama,
USA,
Joined Mar 2000
85
03:37 Jun-16-2005
Re: UT of Austenetic SS
The most effective way to ultrasonically examine SS materials is using Refracted Longitudinal Waves. Generally, dual element focused refracted L-waves (HALT Method) are used to effectively penetrate the dendritic grain structure of the weld.

The HALT Method uses 45, 60, 70 degree Lwaves and OD Creeping Waves (about 80 L) depending on the thickness of the component.

Yes, as indicated before, beam redirection can occur when using shear waves. Some SS materials have no problems with transmission of shearwaves. Low frequency S-waves at 1.5 MHz have been demonstrated effective for examining SS matertials in the US nuclear power plants.

The welding process has a lot to do with the dendrintic grain structure. For example, a TIG welding process may produce a smaller dendrictic grain structure.

However, if you can determine the grain size
of the SS material you may have a better understanding of which wave mode to use. Generally, a grain size of 1 or higher should effectively trasmit S-waves.

When you approach a grain size of 0 or 00, S waves become ineffective.

The best way to prove the effectiveness of using S-Waves or L-Waves, is with a calibration block with Side Drilled Holes at the centerline of the SS weld. AND, with a 10% Notch in the HAZ of one side of the weld. Scanning with the S-wave or L-wave (HALT)Technique (through the weld volume) you can demonstrate adequate penetration, detectability, and sensitivity.

If using Refracted L-Wave Methods (HALT)you must have an understanding of the assoicated S-waves and the effects of mode conversion that takes place with the S-waves. Also, you can not reflect the L-waves off the back surface.

J. Mark Davis

----------- Start Original Message -----------
: : UT is more easy for carbon steels as compared to Austenitic SS. WHY?
: Yes because the Austenitic S/S has a coarse grain structure especially in the welds. The welds and HAZ show a dendritic or columnar grain structure that can redirect shear waves downwards and give you false indications.
------------ End Original Message ------------




    
 
 Reply 
 
Frits Dijkstra, RTD bv Rotterdam, NL
R & D
Applus RTD Technological Center, Netherlands, Joined Jan 2004, 6

Frits Dijkstra, RTD bv Rotterdam, NL

R & D
Applus RTD Technological Center,
Netherlands,
Joined Jan 2004
6
03:21 Jun-17-2005
Re: UT of Austenetic SS
----------- Start Original Message -----------
: UT is more easy for carbon steels as compared to Austenitic SS. WHY?
------------ End Original Message ------------

One thing is that indeed the grains of an austenitic weld are larger than in carbon steel. But that is not the only reason. Another reason, at least as important, is the fact that the grains in austenitic material are anisotropic: they have different properties in different directions. Thus, they have also different sound velocities in different directions. This is not a problem as long as the grains are small compared to the wavelength (which is often the case in the parent metal). But in the coarse-grained weld, every grain boundary acts as a reflector, thus giving noise, scatter and attenuation.

This problem can, in many cases, be solved by using dual angle trandsducers that generate compression waves rather than shear waves. To confirm feasibility for a specific aplication, you will need a representative weld with test reflectors.

Please contact me if you need more information. We could help you out with support and / or probes.


    
 
 Reply 
 
Ed T.
Ed T.
05:08 Jun-17-2005
Re: UT of Austenetic SS
----------- Start Original Message -----------
: : UT is more easy for carbon steels as compared to Austenitic SS. WHY?
: One thing is that indeed the grains of an austenitic weld are larger than in carbon steel. But that is not the only reason. Another reason, at least as important, is the fact that the grains in austenitic material are anisotropic: they have different properties in different directions. Thus, they have also different sound velocities in different directions. This is not a problem as long as the grains are small compared to the wavelength (which is often the case in the parent metal). But in the coarse-grained weld, every grain boundary acts as a reflector, thus giving noise, scatter and attenuation.
: This problem can, in many cases, be solved by using dual angle trandsducers that generate compression waves rather than shear waves. To confirm feasibility for a specific aplication, you will need a representative weld with test reflectors.
: Please contact me if you need more information. We could help you out with support and / or probes.
------------ End Original Message ------------

Are you stating that carbon steel is isotropic? That the direction of sound makes no difference in the acoustic properties of steel?


    
 
 Reply 
 
Uli Mletzko
R & D, Retired
Germany, Joined Nov 1998, 89

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
02:10 Jun-18-2005
Re: UT of Austenetic SS
----------- Start Original Message -----------
: Are you stating that carbon steel is isotropic? That the direction of sound makes no difference in the acoustic properties of steel?
------------ End Original Message ------------

I think, the problem should be divided into three parts:

i) If you have isotropic acoustic properties (i.e isotropic properties for mechanical elastic waves in the grains), the grain size should be no problem. At the border lines between the grains you would have no acoustic impedance difference.

ii) If you have anisotropic acoustic properties (i.e different properties according to the different crystal directions in the grain), then you would have impedance mismatch at a grain boundary, if the grains have different crystal orientation. This will lead not only to attenuation and scatter, but also to distorsion of the direction of sound propagation at the 'micro' level.
But for most of the materials we have a random distribution of the grain orientation. If the appliedwavelength of the ultrasound is large, compared to the average grain size, then we will have a quasi-isotropic situation, and we will not recognize sound path distortion at the 'macro' level, but only attenuation and scatter. This is valid not only for most of the carbon steel materials (including welds), but also for austenitic base materials (bars, plates and pipes), if they are forged or rolled and/or heat treated in a proper manner.

iii) The main problem during ultrasonic testing of castings or welds is caused by the anisotropic crystal growth during solidification, resulting in a dendritic structure or texture. This will lead to large deviations of the sound beam and to skewing, often with unpredictable effects. You can see nice pictures of this in the basic publications e.g. of SILK, OGILVY, NEUMANN or HIRSEKORN.
Sometimes some of the problems can be reduced by use of longitudinal waves or horizontally polarized shear waves, or by applying new imaging procedures like anisotropic SAFT (LANGENBERG et al.). For qualification of procedures the use of 'really' equivalent test specimens (including equivalent welding situation like horizontal or vertical arrangement),is mandatory.
The problem is not restricted to austenitic steels, but appears also in conjunction with nickel alloys AKA Inconel.

Regards
Uli Mletzko
University of Stuttgart (Germany)
MPA, NDT Group


    
 
 Reply 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
06:59 Aug-09-2005
Re: UT of Austenetic SS
Good Day Rich,

You probably mean the other way as far as signal-to-noise ratio is concerned. The signal-to-noise ratio in carbon steel is better compared to that of austenitic stainless steel. Since attenuation of ultrasound is dependent on frequency and since the attenuation is less in carbon steels, one can use a higher frequency signal in carbon steel. Higher frequency results in higher sensitivity and better resolution.

Regards.

S.V.Swamy

----------- Start Original Message -----------
: Good Day Syed,
: Yes, performing Ultrasonic (UT)inspections on Carbon Steel is much easier than Stainless Steel. Carbon steel has a smaller grain structure, hence the ultrasonic waves pass through the material much easier and the signal to noise ratio is much less. Stainless Steel on the other hand contains much larger grain structure and creates a higher signal to noise ratio. You will be able to increase overall UT transducer frequency in Carbon Steel than Stainless Steel, which inadvertently provides more resolution in the test process.
: Regards, Rich Roberts
:
: : UT is more easy for carbon steels as compared to Austenitic SS. WHY?
------------ End Original Message ------------




    
 
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