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Technical Discussions
Ramesh
India, Joined May 2019, 6

Ramesh

India,
Joined May 2019
6
05:48 May-13-2019
ET

Dear All,

In Eddy current, how will you differentiate surface and subsurface defect based on phase angle?

Pls clarify.

    
 
 Reply 
 
John Hansen
Director, - Eddy Current Technology
ETher NDE Ltd, United Kingdom, Joined Oct 1999, 73

John Hansen

Director, - Eddy Current Technology
ETher NDE Ltd,
United Kingdom,
Joined Oct 1999
73
10:08 May-13-2019
Re: ET
In Reply to Ramesh at 05:48 May-13-2019 (Opening).

The signal phase will rotate clockwise. How much this effect is depends on the frequency you use. Higher will give more phase rotation but a smaller amplitude.

There are formulae here https://www.ethernde.com/formulae see items 9-12.

Rgds

John Hansen - ETher NDE

    
 
 Reply 
 
Ramesh
India, Joined May 2019, 6

Ramesh

India,
Joined May 2019
6
10:50 May-13-2019
Re: ET
In Reply to John Hansen at 10:08 May-13-2019 .

Thank You for your clarification.

Meaning that EC signal rotate clockwise for ID defects with low phase angle for surface defects? Pls advice.

Regards

    
 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 746

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
746
16:36 May-14-2019
Re: ET
In Reply to Ramesh at 05:48 May-13-2019 (Opening).

what are you inspecting - tubing or plate ?

    
 
 Reply 
 
J.B.
J.B.
19:19 May-14-2019
Re: ET
In Reply to Anmol Birring at 16:36 May-14-2019 .

zoom image


Impedance Plane

I attach a sketch of the typical impedance plane situation, comparing a surface breaking crack and a rear side open crack... Typical a surface breaking crack moves into similar direction as the lift-off, it works somehow a little like a lift off as material towards the sensor is missing.
The rear side open crack works like a thickness change, which runs opposite (outside the Frequency-Conductivity curve)...
You can do this as an experiment - we did it always in the EN4179 training courses to demonstarte the effects of lift-off, frequency change, conductivity change, thickness measurement, surface open crack, inside/rear side crack, corrosion inspection. I see this as a basic hands-on experiment mandatory already in a level I training.
    
 
 Reply 
 
J.B.
J.B.
19:27 May-14-2019
Re: ET
In Reply to J.B. at 19:19 May-14-2019 .

I forgot:

A perfect Eddy Current Training Tool is provided by University of Magdeburg, Prof. Gerhard Mook, refer to this 2016 WCNDT Publication:
http://www.uni-magdeburg.de/iwfzfp/Download/Publ/2016_WCNDT_Munich_ip1.pdf

Or go for
http://eddycation.de/41265.html

    
 
 Reply 
 
Ramesh
India, Joined May 2019, 6

Ramesh

India,
Joined May 2019
6
02:12 May-17-2019
Re: ET
In Reply to Anmol Birring at 16:36 May-14-2019 .

Dear Anmol,

Can you explain the concept based on tubing?

Regards,
Ramesh

    
 
 Reply 
 
Ramesh
India, Joined May 2019, 6

Ramesh

India,
Joined May 2019
6
02:16 May-17-2019
Re: ET
In Reply to J.B. at 19:27 May-14-2019 .

Hi,

Thanks for your input. Can you send me some stuff based on tubing inspection?

Regards,
Ramesh

    
 
 Reply 
 
J.B.
J.B.
17:22 May-17-2019
Re: ET
In Reply to Ramesh at 02:16 May-17-2019 .

Checkout e.g. the NDT resource center - eddy current section:
https://www.nde-ed.org/EducationResources/CommunityCollege/EddyCurrents/cc_ec_index.htm

There is the page about tube testing - there is a nice animated graphic, where you can virtually move the sensor and watch the Impedance plane:
https://www.nde-ed.org/EducationResources/CommunityCollege/EddyCurrents/Applications/tubeinspection.htm

The site is not totally up-to-date, but the basics do not change. For self-training as well as a resource for some important data the page is worth to be bookmarked in your link list. What is maybe missing regarding your question is the behaviour of encircling coils, but it is comparable to the inside sensors for tubes.

As one of the best reference materials I would recommend the ASNT book about Eddy current testing: https://www.asnt.org/Store/ProductDetail?productKey=3a00253f-97b9-4cc9-8b67-b29567a16d99 but i see, the issue linked here is also more than 20 years old… Also the ASNT Handbook latest issue is (out)dated from 2004 (https://www.asnt.org/Store/ProductDetail?productKey=cd741175-03e7-4ba5-9048-bae3fd01f4d7)
Not the best impression of such a society…
Or checkout the ASTM E series of standards regarding Eddy Current NDT, e.g. ASTM E243 - 18 - Standard Practice for Electromagnetic (Eddy Current) Examination of Copper and Copper-Alloy Tubes (https://www.astm.org/Standards/E243.htm)

Here you find all the ASTM Standards regarding Eddy Current: https://www.astm.org/COMMIT/SUBCOMMIT/E0707.htm
Sorry - it is not for free….
But it represents usually the newest standard information available. Comparable papers are often also available as EN or ISO but in both cases the information is often older when published as the multi nation process to issue those standards takes time...compared to a single nation society like ASTM

    
 
 Reply 
 
J.B.
J.B.
17:48 May-17-2019
Re: ET
In Reply to J.B. at 17:22 May-17-2019 .

Just found in my bookmarks:
… There is some free training material from IAEA, which might be interesting for you:

Eddy Current Testing at Level 2: Manual for the Syllabi Contained in IAEA-TECDOC-628.Rev. 2 "Training Guidelines for Non Destructive Testing Techniques"
(IAEA provides also comparable material on other NDT-Methods, worth to download!!)
https://www-pub.iaea.org/MTCD/Publications/PDF/TCS-48_web.pdf
or
https://inis.iaea.org/collection/NCLCollectionStore/_Public/42/052/42052504.pdf?r=1&r=1


    
 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 746

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
746
03:50 May-18-2019
Re: ET
In Reply to Ramesh at 05:48 May-13-2019 (Opening).

For tubing inspection, the defects are either ID or OD. there are no subsurface defects

    
 
 Reply 
 
Ramesh
India, Joined May 2019, 6

Ramesh

India,
Joined May 2019
6
08:45 May-18-2019
Re: ET
In Reply to Anmol Birring at 03:50 May-18-2019 .

Dear Anmol,

Noted. Can you clarify the basic concept of ID and OD defects with respect to phase angle in tubing inspection?

Regards,

    
 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 746

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
746
16:25 May-18-2019
Re: ET
In Reply to Ramesh at 08:45 May-18-2019 .

When you set freq to f180 and hole to 40 degrees
ID defects will be < 40 deg
OD defects will be > 40 deg

    
 
 Reply 
 
Ramesh
India, Joined May 2019, 6

Ramesh

India,
Joined May 2019
6
11:09 May-22-2019
Re: ET
In Reply to Anmol Birring at 16:25 May-18-2019 .

Thank you for your clarification. In addition to that I need further clarification. In ET, when you carry out inspection on thinner and thicker material eg. Aluminium, thicker material shows increase in resistance compared to thinner material based on impedance plane. Pls clarify.

Regards,

    
 
 Reply 
 

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