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 -
1131 views
Technical Discussions
Pratheesh
NDT Inspector,
India, Joined Aug 2013, 1

Pratheesh

NDT Inspector,
India,
Joined Aug 2013
1
09:04 Aug-21-2013
UT-SURFACE INTERFERENCE

Sound waves refracts when there is transfer of medium.When a material is scanned, couplant is applied B/w the transducer and the material.When the sound travels from the transducer to material first it crosses the couplant and then to the material. I have a doubt that whether is there any refraction happening wen the sound travel from the couplant to material since its a change of medium while using longitudinal waves Or is it negligible.If so wats the reason.

 
 Reply 
 
Gerald R. Reams
Engineering,
Industry, USA, Joined Aug 2012, 181

Gerald R. Reams

Engineering,
Industry,
USA,
Joined Aug 2012
181
16:27 Aug-23-2013
Re: UT-SURFACE INTERFERENCE
In Reply to Pratheesh at 09:04 Aug-21-2013 (Opening).

It generally is not noticeable. I suppose that you may notice changes caused by very thick, viscous, and uneven couplant on a surface that has certain surface discontinuities.

Use Snell's Law to calculate the refracted angle. Anything that causes the sound propagation direction to change from normal incidence will cause it to refract at the interfaces.

Gerald

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

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
17:27 Aug-23-2013
Re: UT-SURFACE INTERFERENCE
In Reply to Pratheesh at 09:04 Aug-21-2013 (Opening).

As a practical matter, normal couplant layers are a very small fraction of a wavelength in thickness and have no effect, but you ask for the theory, so here's the quick explanation.

In theory, since Snell's Law works to bend beams in both directions, you would have refraction at the wedge/couplant interface (bending the incident beam downward since the couplant is slower than plastic) and then at the couplant/metal interface (now bending the beam upward since the metal is faster than couplant). If you do that math based on the longitudinal velocity of your couplant, and then recalculate for plastic (L-wave velocity) to steel (shear wave velocity) you will find that the refracted angle in the metal is the same in either case. In short, the theoretical refraction at the first boundary (plastic/couplant) is cancelled by an opposite effect at the second boundary (couplant/steel) and the net effect is the same as that of a plastic/steel refraction.

1
 
 Reply 
 
Gerald R. Reams
Engineering,
Industry, USA, Joined Aug 2012, 181

Gerald R. Reams

Engineering,
Industry,
USA,
Joined Aug 2012
181
17:45 Aug-23-2013
Re: UT-SURFACE INTERFERENCE
In Reply to Tom Nelligan at 17:27 Aug-23-2013 .

Tom is quite right. His observations hold very true for "normal" conditions. Unfortunately, sometimes the metals we use don't hold up forever to their service or environment.

We all would love to have machined or even ground smooth surfaces to examine but, many times these surfaces are in very poor conditions. That's probably why the customer is having us look. In-service, exposed metals are just difficult to examine sometimes. At least with new fabrication the surface conditions are much better.

 
 Reply 
 

Product Spotlight

Research and Applications Development For NDT

The Research and Applications Development (RAD) group is a newly formed team within Acuren dedicat
...
ed to tackling challenging inspection problems. Our focus is the development of novel, field deployable, advanced inspection techniques for use in cases where standard NDT methods are ineffective. We don't wait for new innovations, we engineer them. From concept to commissioning.
>

Varex Imaging Large Field of View (FOV) Digital Detector Arrays (DDAs)

A larger FOV DDA can reduce the space and volume of the X-ray inspection system on the factory floor
...
, enable faster scanning times, better throughput and better resolution images at a lower dose. Customers can also save time and money. With these benefits in mind, Varex Imaging has designed a family of large FOV detectors (4343HE, XRD 1611, 4343DX-I, 4343CT) for our industrial imaging customers.
>

NEOS III

NEOS III is Logos Imagings lightest DR system. With a built-in battery and internal wireless commu
...
nication, the NEOS III is perfect for users that want to quickly assess an item.
>

Compact NDT inspection-heads for measurements with active thermography

The compact inspection head is suitable for thermographic ndt tasks. The uncooled infrared camera
...
is specially developed for NDI-tasks and offers a thermal sensitivity until now known only from thermal imagers with cooled detector. All required components and functions are integrated into the inspection-head. You will only need an ethernet cable to connect the sensor with the evaluation system.
>

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