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- since 1996 -

Materials Research Institute
Consulting to the NDT industry.

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Technical Discussions
Elmar van den Elzen
Engineering,
Lismar Engineering B.V., Netherlands, Joined Aug 2000, 15

Elmar van den Elzen

Engineering,
Lismar Engineering B.V.,
Netherlands,
Joined Aug 2000
15
04:35 Nov-16-2000
pits in feromagnetic steel

Dear NDT colleagues,

We are looking for a suitable method to measure small pits (typically 1.5mm x 0.5mm x 0.3mm deep) and cracks in a hardened cast steel roll. Normal eddy current testing does not seem to be useful due to very large permeability noise. We tried special weld probes of Zetec without success either. Also a quick try with a 4MHz surface wave probe did not convincingly show the pits either. The rolls are rather large (about 0.5m diameter) and need to be inspected automatically. Does anybody know of a suitable method that’s commercially available? Some approaches we thought about are to use eddy current and magnetically saturate the steel under the probe. Or perhaps Magnetic Flux Leakage would be a possibility?

Regards,
Elmar van den Elzen


    
 
 
Dave Ronson
Dave Ronson
05:56 Nov-16-2000
Re: pits in feromagnetic steel
: Dear NDT colleagues,

: We are looking for a suitable method to measure small pits (typically 1.5mm x 0.5mm x 0.3mm deep) and cracks in a hardened cast steel roll. Normal eddy current testing does not seem to be useful due to very large permeability noise. We tried special weld probes of Zetec without success either. Also a quick try with a 4MHz surface wave probe did not convincingly show the pits either. The rolls are rather large (about 0.5m diameter) and need to be inspected automatically. Does anybody know of a suitable method that’s commercially available? Some approaches we thought about are to use eddy current and magnetically saturate the steel under the probe. Or perhaps Magnetic Flux Leakage would be a possibility?

: Regards,
: Elmar van den Elzen

Are the pits open to the surface? If so a new instrument has been released by RENE, of Van Nuys California, (tele:818-785-1010). It is the 8400K Digitl Optical Micrometer. It lets you measure the width of scratches using the reticle eyepiece and vertical depth of surface features, usually to evaluate the severity of mechanical damage such as scratches, corrosion, pits,or blemishes difficult to observe by other methods. It is rugged and portable and shock resistant. It can be used on convex, concave or any combination of these surfaces.



    
 
 
Richard Kazares
Richard Kazares
03:13 Nov-17-2000
Re: pits in feromagnetic steel
Well - unfortunately there is no "free lunch" in physics. To measure small "things" on a "large" surface almost always requires lots of resolution and time.

In the past, we have appliced Ultrasonic (UT) techniques to find, measure and plot the distribution of extremely fine pits - much less than 1 mm across or deep, on surfaces with many pits. (The problem was to determince the impact damage potential from micro-meteroids in space). This was accomplished with a high-frequency, highly focused UT probe using very fine mechanical scanning resolution.

While this technique would probably be usable in your case - the time needed to accomplish the task might be too long - again depending on the quantity of your samples and the time available to perform the scan.

That (of course) is your decision.


    
 
 
Richard Kazares
Richard Kazares
03:13 Nov-17-2000
Re: pits in feromagnetic steel
Well - unfortunately there is no "free lunch" in physics. To measure small "things" on a "large" surface almost always requires lots of resolution and time.

In the past, we have applied Ultrasonic (UT) techniques to find, measure and plot the distribution of extremely fine pits - much less than 1 mm across or deep, on surfaces with many pits. (The problem was to determince the impact damage potential from micro-meteroids in space). This was accomplished with a high-frequency, highly focused UT probe using very fine mechanical scanning resolution.

While this technique would probably be usable in your case - the time needed to accomplish the task might be too long - again depending on the quantity of your samples and the time available to perform the scan.

That (of course) is your decision.


    
 
 
Richard D. Roberts
Engineering, Executive Managment
Quest Integrity Group, USA, Joined Nov 1998, 78

Richard D. Roberts

Engineering, Executive Managment
Quest Integrity Group,
USA,
Joined Nov 1998
78
05:16 Nov-17-2000
Re: pits in feromagnetic steel
Dear Sir,

Have you considered the use of laser profiling (Laser Profilometry) for your application? If all you are interested in is detection and quantification of very small pits, laser may be the way to go. Laser is not effected by “any” properties in the material such as permeability, external attachments, surface roughness, thickness, etc.

A “off the shelf” system built by QUEST integrated can reliably detect pits with diameters as small as 0.25mm (0.010”) and depths as shallow as 0.127mm (0.050”). QUEST also builds several other systems that have even a higher degree of accuracy. You can locate the QUEST web-site at http://www.qi2.com

Regards,
Rich Roberts

------------------- Origional Message ---------------
: Dear NDT colleagues,

: We are looking for a suitable method to measure small pits (typically 1.5mm x 0.5mm x 0.3mm deep) and cracks in a hardened cast steel roll. Normal eddy current testing does not seem to be useful due to very large permeability noise. We tried special weld probes of Zetec without success either. Also a quick try with a 4MHz surface wave probe did not convincingly show the pits either. The rolls are rather large (about 0.5m diameter) and need to be inspected automatically. Does anybody know of a suitable method that’s commercially available? Some approaches we thought about are to use eddy current and magnetically saturate the steel under the probe. Or perhaps Magnetic Flux Leakage would be a possibility?

: Regards,
: Elmar van den Elzen




    
 
 
Ingo Becker
Engineering, NDT Inspector & Sales
ec-works GmbH, Germany, Joined Apr 2000, 28

Ingo Becker

Engineering, NDT Inspector & Sales
ec-works GmbH,
Germany,
Joined Apr 2000
28
09:09 Nov-20-2000
Re: pits in feromagnetic steel
Hello Elmar,

we think that our eddy current system will be able to detect the pits in your ferromagnetic material.
We have many experience in all kind of eddy current technology and the testing of ferromagnetic materials (even automatic systems in the industries). We develope and produce our own probes as well as our own mechanical and software applications.
Please take a look to our webpages or our NDT forum excibition. The fastest way to get closer to your problem will be a direct talk with our eddy current specialist during his next travell to the Netherlands within the next weeks.

Please contact us via e-mail or telephon: +49 5084-93010

Regards

Ingo Becker

: Dear NDT colleagues,

: We are looking for a suitable method to measure small pits (typically 1.5mm x 0.5mm x 0.3mm deep) and cracks in a hardened cast steel roll. Normal eddy current testing does not seem to be useful due to very large permeability noise. We tried special weld probes of Zetec without success either. Also a quick try with a 4MHz surface wave probe did not convincingly show the pits either. The rolls are rather large (about 0.5m diameter) and need to be inspected automatically. Does anybody know of a suitable method that’s commercially available? Some approaches we thought about are to use eddy current and magnetically saturate the steel under the probe. Or perhaps Magnetic Flux Leakage would be a possibility?

: Regards,
: Elmar van den Elzen




    
 
 
John O'Brien
Consultant, -
Chevron ETC , USA, Joined Jan 2000, 278

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
278
07:23 Nov-20-2000
Re: pits in feromagnetic steel
The pits are very small even for an MFL System. You might look at the SLOFEC technique.
Try contacting Kontroll Teknik in Germany or RTD in Holland.




    
 
 
Zhong Soo Lim
Zhong Soo Lim
01:43 Nov-27-2000
Re: pits in feromagnetic steel
I am working for steel works in Korea.
They have the same problems (permeability variation, mis-call, non-detection) you have mentioned for roll surface inspection using eddy current and ultrasonics.
Magnetic flux leakage method can be applied with good detectibility for the defect size you mentioned.
The inspection time can be easily reduced using multichannel configuration without too much increasing the system cost.
The conventional dc magnetic flux leakage method can be extended to ac method.
I have presented a paper in WCNDT 2000 in Rome.
You can find the paper at
http://www.ndt.net/article/wcndt00/papers/idn217/idn217.htm

If you have further question contact me.

Regards,
Zhong Soo Lim

: Dear NDT colleagues,

: We are looking for a suitable method to measure small pits (typically 1.5mm x 0.5mm x 0.3mm deep) and cracks in a hardened cast steel roll. Normal eddy current testing does not seem to be useful due to very large permeability noise. We tried special weld probes ofZetec without success either. Also a quick try with a 4MHz surface wave probe did not convincingly show the pits either. The rolls are rather large (about 0.5m diameter) and need to be inspected automatically. Does anybody know of a suitable method that’s commercially available? Some approaches we thought about are to use eddy current and magnetically saturate the steel under the probe. Or perhaps Magnetic Flux Leakage would be a possibility?

: Regards,
: Elmar van den Elzen




    
 
 

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