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Technical Discussions
ihsanduzgun
NDT Inspector, NDE Supervisor
Cimtas Piping Industries Ltd. Co., Turkey, Joined Sep 2009, 4

ihsanduzgun

NDT Inspector, NDE Supervisor
Cimtas Piping Industries Ltd. Co.,
Turkey,
Joined Sep 2009
4
15:22 Oct-16-2009
Permanent magnet Yokes

what are the serious disadvantages of permanent magnet yokes vs AC Yokes ?

    
 
 Reply 
 
anjafo
NDT Inspector
Norway, Joined Aug 2009, 204

anjafo

NDT Inspector
Norway,
Joined Aug 2009
204
18:59 Oct-16-2009
Re: Permanent magnet Yokes
In Reply to ihsanduzgun at 15:22 Oct-16-2009 (Opening).

think one of the main ones is that permanent yokes do not agitate the solution meaning mag particles do not form at indication so easily but rather just sit there.

some specs Ive worked out right refuse the use of permanent yokes.

advantages are obviously can be used where power supply is a problem and I think under high heat they are preferred

    
 
 Reply 
 
Nick Welland
Other, Quality and NDT
Aben Technical Services, Australia, Joined Oct 1999, 42

Nick Welland

Other, Quality and NDT
Aben Technical Services,
Australia,
Joined Oct 1999
42
03:15 Oct-17-2009
Re: Permanent magnet Yokes
In Reply to anjafo at 18:59 Oct-16-2009 .

Anjafo,
A major problem relates to the sensitivity to surface defects on heavy sections

http://ammtiac.alionscience.com/pdf/NTN_V29N3.pdf

There have been several follow-ups in subsequent issues of the NTIAC newsletter, and the Australian accreditation body NATA has separated DC/PM as a discrete MT method, requiring a proven procedure and specifying material maximum thickness.
Regards,
Nick

    
 
 Reply 
 
Kandula
Kandula
09:50 Oct-22-2009
Re: Permanent magnet Yokes
In Reply to ihsanduzgun at 15:22 Oct-16-2009 (Opening).

hi,
The serious disdvantage is here the magnetic medium losess its mobility gives a furious indications all over test area, u cant vary the magnetic flux intensity value, magn medium sticke to yoke legs needs to be clean up during each inspection

    
 
 Reply 
 

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