where expertise comes together - since 1996

Web's Largest Portal of Nondestructive Testing (NDT)
Open Access Database (Conference Proceedings, Articles, News), Exhibition, Forum, Network

All Forum Boards
Technical Discussions >
Eddy Current V's DPI/MPI
Career Discussions
Job Offers
Job Seeks
Classified Ads
About NDT.net
Articles & News

2797 views
00:10 Nov-05-2009

anjafo

NDT Inspector
Norway,
Joined Aug 2009
204
Eddy Current V's DPI/MPI

Would Eddy Current find everything DPI/MPI could?

 
08:30 Nov-05-2009

Godfrey Hands

Engineering,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
286
Re: Eddy Current V's DPI/MPI In Reply to anjafo at 00:10 Nov-05-2009 (Opening).

Hi Anjafo,
In theory, Eddy Current should find everything that DPI or MPI will, but there are certain limitations.

MPI is field direction sensitive, so you need to be certain that you have covered the component or area with crossing magnetic fields.
The same is applicable to Eddy Current. This will not easily detect a crack when the probe runs along the length of the crack, so once again, you need to double inspect at right angles to the first inspection to be certain of detecting the cracks.

Also when it comes to borderline defect dimensions, there are some limitations.
In a laboratory environment with experimental Eddy Current equipment, we have been sucessful in reliably detecting cracks of 0.020mm deep, whilst with a very sensitive penetrant or magnetic test, detection of smaller defects could be possible. Here however surface finish is critical for all three methods.

Eddy current can also detect defects under a thin non-conductive coating (like MT, but unlike PT).

Regards,

Godfrey

 
20:32 Nov-05-2009

Jim Draper

Consultant, ASNT Level III MT PT RT VT
Draper NDT,
USA,
Joined Jul 2009
99
Re: Eddy Current V's DPI/MPI In Reply to Godfrey Hands at 08:30 Nov-05-2009 .

DPI will is not limited to electricaly conductive material. Also, I have used direct current fluorescent MPI to locate flaws 1/4" deep. Of course that is limited to ferromagnetic material, while eddy current can be used to test other electricaly conductive materials.

 


© NDT.net - The Web's Largest Portal of Nondestructive Testing (NDT) ISSN 1435-4934

Open Access Database, |Conference Proceedings| |Articles| |News| |Exhibition| |Forum| |Professional Network|