where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -

1219 views
Technical Discussions
Arianna Macchi
Consultant
Italy, Joined Apr 2005, 6

Arianna Macchi

Consultant
Italy,
Joined Apr 2005
6
09:01 Jun-06-2005
Couplant for porous stones

Dear colleagues

I'm trying to perform simple UT attenuation measurements on porous stones with a 500 KHz contact transducer in pulse-echo configuration. I'm using vaseline as couplant but I've noticed that when the couplant begins to melt (i.e. becomes more fluid) the sensitivity decrease significantly. By suppyling a new amount of fresh (more solid) substance, things get better, but this happens every 10-15 seconds.

Can you suggest me some possible alternative to vaseline??


    
 
 
John Brunk
Engineering, NDT Level III
Self employed, part-time, USA, Joined Oct 1999, 158

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
158
03:13 Jun-06-2005
Re: Couplant for porous stones
----------- Start Original Message -----------
: Dear colleagues
: I'm trying to perform simple UT attenuation measurements on porous stones with a 500 KHz contact transducer in pulse-echo configuration. I'm using vaseline as couplant but I've noticed that when the couplant begins to melt (i.e. becomes more fluid) the sensitivity decrease significantly. By suppyling a new amount of fresh (more solid) substance, things get better, but this happens every 10-15 seconds.
: Can you suggest me some possible alternative to vaseline??
------------ End Original Message ------------

Your data will be altered by couplant entering pores in the samples. You should use self-coupling (dry coupling)transducers. I have used these successfully to examine a variety of porous materials. One source for these is Ultran. If you can't obtain new transducers you might be able to use sheet dental adhesive as a coupling layer. Attenuation will then vary with pressure but maybe you could measure the difference between the first and second back reflections. You should try to get the vaseline out of your samples and re-test them.


    
 
 
Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
03:16 Jun-06-2005
Re: Couplant for porous stones
Several companies (including mine) offer very high viscosity ultrasonic couplants for use with normal incidence shear wave transducers. That sort of medium also works well for coupling longitudinal wave transducers on porous materials, because the very high viscosity limits absorption. I'd suggest that you try a commercial shear wave couplant.

Tom Nelligan
Senior Applications Engineer
Panametrics-NDT, a business of R/D Tech
www.panametrics-ndt.com


----------- Start Original Message -----------
: Dear colleagues
: I'm trying to perform simple UT attenuation measurements on porous stones with a 500 KHz contact transducer in pulse-echo configuration. I'm using vaseline as couplant but I've noticed that when the couplant begins to melt (i.e. becomes more fluid) the sensitivity decrease significantly. By suppyling a new amount of fresh (more solid) substance, things get better, but this happens every 10-15 seconds.
: Can you suggest me some possible alternative to vaseline??
------------ End Original Message ------------




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

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
176
09:16 Jun-07-2005
Re: Couplant for porous stones
Reply

Hello,
coming back to the original task: Determination of sound attenuation:
On porous stones, I suppose, it can only be measured for longitudinal waves, and only using the through-transmission technique, with separate transmitter and receiver probes on opposite sides of the sample.
And this can only be a relative measurement compared to a reference sample, using always the same equipment and same set-up.
Losses by changing coupling conditions and by changing divergence losses of the sound beams from sample to sample are much bigger than the losses by attenuation (scattering) in the objects itself.
As mentioned in the replies from collegues before, the change of the elastic properties of couplant during measurement will change the sound transfer conditions (decreasing transmissivity at the boundaries. But filling the pores of your object with liquid will improve transmission in the object. So depending on the measurement conditions (time) the calculated attenuation coefficient will bea random figure.
On porous materials a valid relative attenuation coefficient can only be achieved by dry coupling conditions i.e. using dry coupling probes in a rig (probes aligned controlled pressure) or very thin foils between probes and sample to avoid pentration of a fluid couplant.

Kind regards
Udo Schlengermann
Applications Laboratory
GE Inspection Technologies GmbH
Huerth, Germany


----------- Start Original Message -----------
: Dear colleagues
: I'm trying to perform simple UT attenuation measurements on porous stones with a 500 KHz contact transducer in pulse-echo configuration. I'm using vaseline as couplant but I've noticed that when the couplant begins to melt (i.e. becomes more fluid) the sensitivity decrease significantly. By suppyling a new amount of fresh (more solid) substance, things get better, but this happens every 10-15 seconds.
: Can you suggest me some possible alternative to vaseline??
------------ End Original Message ------------




    
 
 

Product Spotlight

FMC/TFM

Next generation for Phased Array UT is here now with FMC/TFM! Have higher resolution imaging, impr
...
oved signal to noise ratio, characterize, size and analyze defects better with access to several wave mode views and save raw FMC data for higher quality analysis.  Some of the benefits are:
  • Beautiful Image! Easier to understand what you're looking at
  • Completely focused in entire image or volume
  • Much easier to define setups before inspection
  • Easier to decipher geometry echoes from real defects
  • Oriented defects (e.g. cracks) are imaged better
  • See image from different wave modes from one FMC inspection
  • FMC data can be reprocessed/analyzed without going back to the field
>

Webinar: Improving Heat Exchanger Inspection Analysis

Zetec will host a webinar on automated analysis software for more effective heat exchanger inspectio
...
ns in power generation, oil & gas, pharmaceutical manufacturing & other applications. Register now. We will demonstrate how to reduce inefficiencies from legacy acquisition techniques so analysts can focus on identifying signals of interest, evaluating them & making confident decisions.
>

Conformable wedge transducer

The conformability is obtained with a flexible membrane filled with water between the transducer and
...
the inspected component. The coupling between the membrane and the component requires a small quantity of water or couplant. The conformable wedge combines the acoustic performance of immersion technique with good coupling and low attenuation.
>

NEW - TD Focus-ScanRX

The NEW Next Generation Advanced UT platform, TD Focus ScanRX - Also available as a card stack solut
...
ion. Key Improvements 1. Data acquisition is significantly faster than current design 2. Better aesthetic – closely aligns with HandyScan RX 3. Improved IP rating (Target IP66) 4. Ruggedized housing 5. Connectors are protected from impact and ingress 6. Integrated stand and separate retractable handle easy to keep clean) 7. Touchscreen with ruggedized display glass 8. 3-Axis encoder input
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window