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1571 views
09:07 Jan-24-2010

ram

NDT Inspector, -
Kuwait,
Joined Jan 2010
13
grain size

DEAR ALL,
is it possible to measure the grain size of metal or weld metal using UT?
if it is what is the procedure?
regards
rama

 
18:03 Jan-24-2010

Wieslaw Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
238
Re: grain size In Reply to ram at 09:07 Jan-24-2010 (Opening).

It is possible, but it requires, that scattering on grains is measured. Maximum scattering should be observed, if the wavelength is ten times larger than grain size. Most standard ultrasonic flaw detectors are not sufficient for this measurement.

 
19:25 Jan-24-2010

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
Re: grain size In Reply to Wieslaw Bicz at 18:03 Jan-24-2010 .

And, in addition, I think that the grain (crystal) orientation should be random. Only then you have macroscopic isotropy and thus it is negligible, wether the microscopic individual mechanical grain properties are isotropic or anisotropic.
If, in contrary, you have macroscopic anisotropy (texture) or dendritic grain growth (like in austenitic stainless castings or welds), then all is much more difficult, and grain sizing by UT might be impossible.

Regards
Uli Mletzko

 
15:20 Jan-25-2010

jifeng zhao

R & D, ndt inspector,engineering
Hebei power,
China,
Joined Jan 2010
4
Re: grain size In Reply to ram at 09:07 Jan-24-2010 (Opening).

It's certainly possible.
There are some certain relations between the attenuation coefficient or sound velocity and the grain size. But as to different materials, there are different laws. and it seems that this subject has been being researched recent years.
Just as what Mr. Uli Mletzko said, if the material is macroscop anisotropy, it may become difficult to measure the grain size using UT. And we know, most of welds and casts are of columnar grain or dendritic grain, which means they are macroscop anisotropy.

 
15:21 Jan-25-2010

Robert Paynter

R & D, Research Assistant
U of Oxford,
United Kingdom,
Joined Jun 2001
14
Re: grain size In Reply to ram at 09:07 Jan-24-2010 (Opening).

I don't think so:
The largest metal grain sizes are typically of the orders of millimetre, and that's in slowly cooling castings. Most grains are of 10s of micrometre scales, specially in the relatively fast cooling environment of a weld. The grain boundaries are, usually a few atoms wide, ie nanometres. The smallest wavelengths of Ultrasound in metals are of the order of 100s of micrometres. It's impossible to distinguish separate objects of less than about 1/2 wavelength, so you will not be able to see that grain boundaries. Another reason is that they are, at best, going to be a bit like another shade of grey, with a slightly different refractive index.
X-ray tomography is able to pick out grains, but it has to be able to get all the way round a fairly small object - is that the scale you are thinking of?

Here's an example presentation from ESRF:
http://ftp.esrf.eu/pub/scisoft/fable/talks/workshop_April_2009/GrainMappingTomography_Ludwig.pdf

note the summary :
Acquisition time:2h
1008 reconstructed grains
2 days of processing (30 nodes)
approx. 3 micrometre accuracy

ESRF is NOT a portable measurement device: www.esrf.eu/AboutUs/AboutSynchrotron

 
16:07 Jan-25-2010

Wieslaw Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
238
Re: grain size In Reply to Robert Paynter at 15:21 Jan-25-2010 .

You are writing, that: "It's impossible to distinguish separate objects of less than about 1/2 wavelength, so you will not be able to see that grain boundaries."

It is not correct. To be able to recognize the grain size you do not need to visualize them. It is fully enough to measure the scattering. And this occurs at wavelengths that are many times larger than grain size. It is possible to measure grain size with ultrasound and such measurements are known and used since years, but naturally not good in each possible case.

If this is applicable, the method is simple and quick - this can be the large advantage.

 
11:37 Jan-26-2010

Andrey Bazulin

R & D, -
Scientific Center ECHO+,
Russia,
Joined Sep 2006
57
Re: grain size In Reply to Wieslaw Bicz at 16:07 Jan-25-2010 .

Of course it is possible to estimate the grain size by measurement of ultrasound attenuation in the reference blocks at different frequencies.
In Russia this method spreading widely, particularly it Railways (axis, wheels, rails materials)...
We have a special code for example (Ð? 153-34.1-17.404-00)

 
20:30 Jan-27-2010

Robert Paynter

R & D, Research Assistant
U of Oxford,
United Kingdom,
Joined Jun 2001
14
Re: grain size In Reply to Wieslaw Bicz at 16:07 Jan-25-2010 .

I accept your correction - perhaps I should study scattering etc. - my experience is too much theoretical and microscopic.

So, do you need standard samples with known grain-size (measured by microscope) to provide calibration? Presumably you will need samples very similar to the weld you are measuring.

Robert

 


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