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Technical Discussions
JAGAN
Engineering,
Saudi Arabia, Joined Dec 2011, 23

JAGAN

Engineering,
Saudi Arabia,
Joined Dec 2011
23
12:14 Nov-19-2014
depth of Eddy currents

Hi

Can any body can share the information that up to what extend eddy currents can penetrate inside the materiel, i mean depth of penetration in different meterials.
based on which code.

Thanks.

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 893

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
893
13:14 Nov-19-2014
Re: depth of Eddy currents
In Reply to JAGAN at 12:14 Nov-19-2014 (Opening).

Jagan,

Depth of penetration with Eddy Current in materials is dependent on the material and it's characteristics as well as the frequency used. The depth of penetration is not based on code, but on mathematical formulas.

 
 Reply 
 
Matthias
NDT Inspector, CEO
Dreifeld Materialprüftechnik, Germany, Joined Sep 2005, 105

Matthias

NDT Inspector, CEO
Dreifeld Materialprüftechnik,
Germany,
Joined Sep 2005
105
13:14 Nov-19-2014
Re: depth of Eddy currents
In Reply to JAGAN at 12:14 Nov-19-2014 (Opening).

I'm sorry that I can't answer with just one number (that's what you are probably looking for).

It depends on the frequency of the probe/device, the electric conductivity of the material, and the relative permeability. With those values you can calculate the depth in mm, but keep in mind that you still have to consider a few things like: what thickness is the material? If it is thin (less than 10mm) you have to calculate the right frequency you have to use. What size of defects are you looking for? The calculation for the single depth is: 503 devided by root of frequency x conductivity x permeability

If you don't have ET2 you should consider contacting someone who has the certification.

1
 
 Reply 
 
JAGAN
Engineering,
Saudi Arabia, Joined Dec 2011, 23

JAGAN

Engineering,
Saudi Arabia,
Joined Dec 2011
23
13:22 Nov-19-2014
Re: depth of Eddy currents
In Reply to Matthias at 13:14 Nov-19-2014 .

Matthias,
I know the formula to calculate by using conductivity & permeability
i want to inspect inconel625 meterial of 45mm thickness i need to know upto wat depth we can inspect by using surface eddy currents...
i was unable to calculate for this meterial

 
 Reply 
 
langtuteng
Armenia, Joined Nov 2014, 199

langtuteng

Armenia,
Joined Nov 2014
199
13:22 Nov-19-2014
Re: depth of Eddy currents
In Reply to JAGAN at 12:14 Nov-19-2014 (Opening).

hi JAGAN , the depth of the eddy current penetrate due to the frequency, electrical conductive and magnetic conductive . you can use the formula δ=503.3/√fμrσ which is for the ferro-magnetic material.

 
 Reply 
 
Esmaeel Ahmadzade
Engineering,
ferdowsi university of mashhad, Iran, Joined May 2011, 11

Esmaeel Ahmadzade

Engineering,
ferdowsi university of mashhad,
Iran,
Joined May 2011
11
13:26 Nov-19-2014
Re: depth of Eddy currents
In Reply to JAGAN at 12:14 Nov-19-2014 (Opening).

zoom image



zoom image






Dear Jagan,
i uploaded a figure and a equation describing how penetration depth changes with 3 factors of f(frequency), magnetic permeability and electrical conductivity.regard,
 
 Reply 
 
Matthias
NDT Inspector, CEO
Dreifeld Materialprüftechnik, Germany, Joined Sep 2005, 105

Matthias

NDT Inspector, CEO
Dreifeld Materialprüftechnik,
Germany,
Joined Sep 2005
105
13:32 Nov-19-2014
Re: depth of Eddy currents
In Reply to Esmaeel Ahmadzade at 13:26 Nov-19-2014 .

Esmaeel, great diagrams.

 
 Reply 
 
JAGAN
Engineering,
Saudi Arabia, Joined Dec 2011, 23

JAGAN

Engineering,
Saudi Arabia,
Joined Dec 2011
23
13:50 Nov-19-2014
Re: depth of Eddy currents
In Reply to Esmaeel Ahmadzade at 13:26 Nov-19-2014 .

Mr.Esmaeel,

Thanks for the diagrams
Could you please share about that what will be the values i mean the permiabilty and resistivity values to calculate depth for inconnel 625 material.
im unable to get those values for inconnel625

 
 Reply 
 
Esmaeel Ahmadzade
Engineering,
ferdowsi university of mashhad, Iran, Joined May 2011, 11

Esmaeel Ahmadzade

Engineering,
ferdowsi university of mashhad,
Iran,
Joined May 2011
11
14:36 Nov-19-2014
Re: depth of Eddy currents
In Reply to JAGAN at 13:50 Nov-19-2014 .

use 4Pi e-7(Henry/m) for permeability and 7.7519e+5(s/m) for conductivity.

 
 Reply 
 
John Hansen
Director, - Eddy Current Technology
ETher NDE Ltd, United Kingdom, Joined Oct 1999, 74

John Hansen

Director, - Eddy Current Technology
ETher NDE Ltd,
United Kingdom,
Joined Oct 1999
74
19:10 Nov-19-2014
Re: depth of Eddy currents
In Reply to Esmaeel Ahmadzade at 13:26 Nov-19-2014 .

Hi Jagan

The Graph shown assumes an infinite size probe into an infinite half space and shows the point where half the current flows above this point and half below and the usual limit is 3 standard depth of penetration. This is because the field decays exponentially with distance.

SO the graph is a simplification.

You need to take into account the dimensions of the probe as for instance it is inconceivable .

My rule of thumb is the probe drivee col needs to be more than 3 times larger than the depth required to penetrate to.

Rgds

John Hansen - MD ETher NDE
www.ethernde.com

1
 
 Reply 
 
Frank Lund
R & D,
United Kingdom, Joined Apr 2005, 222

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
222
19:38 Nov-19-2014
Re: depth of Eddy currents
In Reply to JAGAN at 13:50 Nov-19-2014 .

This link gives the resistivity. It was very easy to find.

http://www.azom.com/article.aspx?ArticleID=4461

For non-magnetic materials use Relative Permeability = 1

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 893

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
893
21:33 Nov-19-2014
Re: depth of Eddy currents
In Reply to Frank Lund at 19:38 Nov-19-2014 .

Jagan,

At that thickess why not use UT?

 
 Reply 
 
JAGAN
Engineering,
Saudi Arabia, Joined Dec 2011, 23

JAGAN

Engineering,
Saudi Arabia,
Joined Dec 2011
23
07:39 Nov-20-2014
Re: depth of Eddy currents
In Reply to Michel Couture at 21:33 Nov-19-2014 .

Mr.Michel,
We are looking for surface breaking cracks thats why im using ET,which is more sensitive than other NDE methods

 
 Reply 
 
joel nyaga
joel nyaga
12:47 Nov-20-2014
Re: depth of Eddy currents
In Reply to JAGAN at 07:39 Nov-20-2014 .

Jagen, for surface breaking cracks/defects, the most sensitive is FPI method of detection. For eddy current method is for both surface and subsurface cracks however for certain metals for instance inconel, you would need to know its conductivity and permeability values prior to test, the type of coil to be used and if a 100% coverage is desired. FPI will provide all that if surface breaking cracking is being sought and that is what is recommended for in aerospace esp. inspection of inconel bolts for the wheels and engine bolts. ULTRASONIC insp won't solve your query if you are looking surface breaking defects not unless you inspect from one side to get indications from the opposite side and vice versa ie determining the back reflection signals variations just as we do thickness measurement using a twin crystal element. still for me i would prefer you to use FPI.

 
 Reply 
 
jagan
Engineering,
Saudi Arabia, Joined Dec 2011, 23

jagan

Engineering,
Saudi Arabia,
Joined Dec 2011
23
13:22 Nov-20-2014
Re: depth of Eddy currents
In Reply to joel nyaga at 12:47 Nov-20-2014 .

I agree with you Mr.Joel.
I know that
where ever accessible i'm doing phased array for for the internal defects
and for surface n subsurface internally and externally with right angled absolute probe.

FPI means florescent...???

And suggest me if you have any other ideas to get 100% NDE on WELDOLET...????
Inconnel of 45mm flat thickness in the middle and weld bewel on the bottom neck n top neck.

 
 Reply 
 
joel nyaga
joel nyaga
05:35 Nov-21-2014
Re: depth of Eddy currents
In Reply to jagan at 13:22 Nov-20-2014 .

unfortunately i don't work on butt weld joints but have tested some of them and i used flourescent penetrant insp. i advise you on the same.

 
 Reply 
 
langtuteng
Armenia, Joined Nov 2014, 199

langtuteng

Armenia,
Joined Nov 2014
199
15:09 Nov-23-2014
Re: depth of Eddy currents
In Reply to jagan at 13:22 Nov-20-2014 .

FPI refers to the fluorescence penetrate inspection.

 
 Reply 
 
langtuteng
Armenia, Joined Nov 2014, 199

langtuteng

Armenia,
Joined Nov 2014
199
15:13 Nov-23-2014
Re: depth of Eddy currents
In Reply to joel nyaga at 12:47 Nov-20-2014 .

hi , the most sensitivity method FPI is used to inspect the surface breaking cracks, but for the subsurface cracks, i think ET or MT is suitable.

 
 Reply 
 

NDT Inspector,
China, Joined Jul 2014, 26


NDT Inspector,
China,
Joined Jul 2014
26
03:18 Dec-21-2014
Re: depth of Eddy currents
In Reply to jagan at 13:22 Nov-20-2014 .

Hi JAGAN,

Would you mind provide your drawing of bevel? Are the body material and the fill material all inconel 625, or just the fill material is?

I know a similar project, provide the drawing, maybe I can help.

 
 Reply 
 
JAGAN
Engineering,
Saudi Arabia, Joined Dec 2011, 23

JAGAN

Engineering,
Saudi Arabia,
Joined Dec 2011
23
05:10 Dec-21-2014
Re: depth of Eddy currents
In Reply to at 03:18 Dec-21-2014 .

This not weld inspection
its meterial inspection.

 
 Reply 
 

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