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Technical Discussions
Jedispin
Jedispin
06:59 Aug-18-2009
Subsurface crack detection by MT in Martensitic Stainsless Steel

Hi,

I would like to have some information regarding subsurface crack detection by MT in Martensitic Stainsless Steel. I would like to know, what is the maximum depth that we can detect such a crack for martensitic stainless steel.

Do a study has been already done regarding subsurface crack detection on different material.

    
 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 845

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
845
03:57 Aug-19-2009
Re: Subsurface crack detection by MT in Martensitic Stainsless Steel
In Reply to Jedispin at 06:59 Aug-18-2009 (Opening).

Hi,

I will answer your question assuming that you are inspecting parts of that material on a regular basis. Maybe you should get a Ketos Ring of a similar material. This way, you will be able to properly verify the sensitivity of your system and will know exactly how deep you can go. The drawing can be found in ASTM E1444.

    
 
 Reply 
 
John Brunk
Engineering, NDT Level III
Self employed, part-time, USA, Joined Oct 1999, 160

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
160
06:46 Aug-19-2009
Re: Subsurface crack detection by MT in Martensitic Stainsless Steel
In Reply to Jedispin at 06:59 Aug-18-2009 (Opening).

Martensitic stainless steels, including maraging steel that has not been heat
treated to reform a substantial percentage of austenite, has extremely
limited depth of penetration for very low-frequency eddy current inspection.
Based on this I would be surprised if you could detect subsurface defects with
an electromagnetic yoke. With full-wave rectified current and high amperage
and a Ketos-type ring as Michel suggested, you might find an answer that
pleases you. There are both ferromagnetic and non-ferromagnetic forms of
martensite, but the ferromagnetic form structure often predominates, especially
in maraging steels.

    
 
 Reply 
 

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