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Technical Discussions
corrine
Engineering,
USA, Joined Nov 2011, 13

corrine

Engineering,
USA,
Joined Nov 2011
13
15:23 Jan-25-2012
MT STAINLESS

I came across something interesting....doing an experament on this today...I have some parts made of a stainless that is strongly attracted to a magnetic field ( has some hybrid number for material type ) I have tried to shot this thing with mag and have yet to be able to creat a field in the part....I used QQI and a hall effect metter. anyone have any idea or experiance with this. I was told by a gentalman that stainless has a very different hysteriss loop. I'd like to know more if anyone has any insite on this. Thanks You

 
 Reply 
 
Ed T.
Ed T.
17:40 Jan-25-2012
Re: MT STAINLESS
In Reply to corrine at 15:23 Jan-25-2012 (Opening).

It's been a while for me, but if I'm not mistaken, there ae some Type 400 series of Stainless Steel that are ferromagnetic. Someone correct me if I'm wong. I remember in the old days, I ran into Stainless valves that were magnetic.

 
 Reply 
 
corrine
Engineering,
USA, Joined Nov 2011, 13

corrine

Engineering,
USA,
Joined Nov 2011
13
21:45 Jan-25-2012
Re: MT STAINLESS
In Reply to Ed T. at 17:40 Jan-25-2012 .

these parts are little and wouldnt fit between the head...but i butted up a CC and shot one .... the QQI showed the indication in the right direction at 400 amps. Now unless everything that is said about the QQI being able to be used for field strenght and direction...the it's able to be magnitised....the part is attracted strongly to a magnet. so now I'm trying to shot it in a magnaflux " Flat Coil".....this is where the wierd began in this project.

 
 Reply 
 
Ulf Hansen
Director, CSM NDT Certification
CSM NDT Certification / Exova, Sweden, Joined Aug 2011, 30

Ulf Hansen

Director, CSM NDT Certification
CSM NDT Certification / Exova,
Sweden,
Joined Aug 2011
30
23:04 Jan-25-2012
Re: MT STAINLESS
In Reply to corrine at 21:45 Jan-25-2012 .

zoom image



Hi

Stainless steels only allowed with chromium are ferromagnetic, they belong to the ferritic or martensitic group. So, yes, some stainless steel may be MT-tested.

Please look out for duplex steels (around 5% nickel), they may cause false indications due to differences between the magnetic properties between ferrite and austenite.This is especially true regarding heavy castings with coarse microstructure. Please take a look at a photo which I attached to this message.

Best regards /Ulf
 
 Reply 
 
John Brunk
Engineering, NDT Level III
Self employed, part-time, USA, Joined Oct 1999, 162

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
162
23:32 Jan-25-2012
Re: MT STAINLESS
In Reply to corrine at 21:45 Jan-25-2012 .

ASTM E 1444 has a useful diagram listing steels that are ferromagnetic, ferromagnetic only after heat treatment, and always non-ferromagnetic. There are some surprises. For example, 17-4 PH stainless steel is ferromagnetic only after it has been properly heat treated. 15-5 PH is ferromagnetic in the annealed state as well as after heat treatment. Because these stainless steel have much lower magnetic permeability than carbon steels, they need relatively more field strength to be sufficiently magnetized and also have higher retentivity

 
 Reply 
 
corrine
Engineering,
USA, Joined Nov 2011, 13

corrine

Engineering,
USA,
Joined Nov 2011
13
23:54 Jan-25-2012
Re: MT STAINLESS
In Reply to John Brunk at 23:32 Jan-25-2012 .

I checked the chart in 1444 and i didnt see AISI E 52100. The breeak down shows no Nickel. C-.980-1.10%, CR is 1.30-1.60%, Fe 96.5-97.32%, Mn .250-.450%, P .0250%, sI .150-.330%,s .0250%. I'M new to QQI's and the placement of the QQI seems to have some tricks to it. these are small aprox 1 inch length X.5" dia

 
 Reply 
 
John A Brunk
Engineering, NDT Level III
Self employed, part-time, USA, Joined Oct 1999, 162

John A Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
162
01:34 Jan-26-2012
Re: MT STAINLESS
In Reply to corrine at 23:54 Jan-25-2012 .

AISI E 52100 is strongly ferromagnetic. The QQI shim must be carefully attached so it is in intimate contact with the part surface so that none of the magnetic particle suspension gets between it and the test surface. The length to diameter ratio of 2:1 is too short for good conventional coil magnetization. Can you put two together to make it 4:1 and try to magnetize them that way? I have used a flat coil in the shape of an Archimedes spiral with good results but I have not used the type of flat coil you mentioned. It appears to be something quite different. Do you have a conventional coil or an electromagnetic yoke available??

 
 Reply 
 
Uli Mletzko
R & D, Retired
Germany, Joined Nov 1998, 89

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
11:27 Jan-26-2012
Re: MT STAINLESS
In Reply to corrine at 15:23 Jan-25-2012 (Opening).

Besides stainless steels, which are ferromagnetic due to their intended alloy composition, there are some interesting magnetic effects in relation to austenitc stainless steel (ASST).

Two examples:

(i) When welding ASST plates or pipes, then in the weld material there is a certain content of 'delta ferrite', which is magnetizable. So, if you have ASST components, which are grinded or milled, you can find very easy the position of weldments by using a little magnet.

(ii) When deforming ASST material, e.g. at tensile or bending specimens during materials evaluation, then due to the plastification there is created 'deformation martensite', which is magnetizable, too. So you can find areas of high deformation by using MT methods.

Regards
Uli Mletzko
(retired from MPA Stuttgart)

1
 
 Reply 
 
Norm Woodward
Norm Woodward
17:28 Jan-26-2012
Re: MT STAINLESS
In Reply to John Brunk at 23:32 Jan-25-2012 .

Thanks for your timely reference.

You saved me a trip to the flight line, where I was going to sort possible titanium alloy fastners from A-286 CRES (and PH 13-8 Mo) steel fasteners, using a magnet.

That could have been embarassing...

 
 Reply 
 
P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
21:40 Jan-26-2012
Re: MT STAINLESS
In Reply to John Brunk at 23:32 Jan-25-2012 .

Dear Sir,
To my knowledge both 17-4PH and 15-5PH steels are predominantly martensitic in annealed condition and as such ferromagnetic. Both are precipitation hardened/age hardened to get higher strength by way precipitating a fine copper containing phase in the martensitic matrix .The main difference is the higher delta ferrite content in 17-4 PH which lowers the toughness. The delta ferrite is minimized in the 15-5PH steel by careful control of the processing and this gives better toughness to the steel (about 15% elongation against 10% for 17-4PH for the same heat treatment condition.
It is the 17-7PH steel which is semi-austenitic steel which after heat treatment at low temperature, turns martensitic and exhibits ferromagnetic property.
Regards,
P V SASTRY

 
 Reply 
 
Amy
NDT Inspector, - -
USA, Joined Jan 2009, 87

Amy

NDT Inspector, - -
USA,
Joined Jan 2009
87
15:55 Jan-30-2012
Re: MT STAINLESS
In Reply to P V SASTRY at 21:40 Jan-26-2012 .

We see quite a few of these materials. The biggest problem with them is identification and proper testing. The material or part at manufacturing is usually tested with penetrant and somewhere further down the line MT is requested. 17-4 PH although ferromagnetic has a large number of "false calls" due to misinterpretation of very real and visible indications. Most of these parts are inservice parts and typically not accompanied by a drawing or material identification. When personnel are testing for linear indications that could easily be attributed to a subsurface condition or other material condition that has never been observed before (due to the part was PT tested) it can create a large number of false calls. I try not to recommend MT on these materials unless no other feasible or available method is available.

Ulf..Great picture. We've observed similar results.

Here's an article in the old ASNT back to basics files about NDT of Precipitation Hardened Steels Using Fluorescent Magnetic Particle Testing by Bob Potter

http://www.asnt.org/publications/materialseval/solution/dec03solution/dec03sol.htm

 
 Reply 
 
John Brunk
Engineering, NDT Level III
Self employed, part-time, USA, Joined Oct 1999, 162

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
162
00:01 Jan-31-2012
Re: MT STAINLESS
In Reply to P V SASTRY at 21:40 Jan-26-2012 .

I made an error in an earlier post. 17-4 PH is always ferromagnetic, although the magnetic permeability does increase when heat treated to higher hardnesses. It is 17-7 PH that must be heat treated prior to magnetic particle inspection. Based on many tests with notched shims we decided as a practical matter to test certain parts of both alloys after heat treatment.

 
 Reply 
 
Ulf Hansen
Director, CSM NDT Certification
CSM NDT Certification / Exova, Sweden, Joined Aug 2011, 30

Ulf Hansen

Director, CSM NDT Certification
CSM NDT Certification / Exova,
Sweden,
Joined Aug 2011
30
07:48 Jan-31-2012
Re: MT STAINLESS
In Reply to John Brunk at 00:01 Jan-31-2012 .

Hi

Forgot to mention that the photo I attached was from a cast VK A378 material. We generally use PT on these "spooky" steel alloys.
BR/Ulf

 
 Reply 
 
Ondrej Holas
Ondrej Holas
22:36 Apr-30-2013
Re: MT STAINLESS
In Reply to Ulf Hansen at 07:48 Jan-31-2012 .

Hi! I am writing a bachelor thesis about magnetic testing of duplex steel. I also detect false indications. I did a metalography on a couple of specimens and tried to find a connection between austenite and the indications, but it came out incoclusive. Does anyone have any new information on this subject?

 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
11:36 May-01-2013
Re: MT STAINLESS
In Reply to Ondrej Holas at 22:36 Apr-30-2013 .

Penetrant test Duplex - slower but less confusing

 
 Reply 
 
Cesar Tovar
NDT Inspector, Quality assurance Representative
Toronto Transit Commission, Mexico, Joined Sep 2014, 7

Cesar Tovar

NDT Inspector, Quality assurance Representative
Toronto Transit Commission,
Mexico,
Joined Sep 2014
7
08:07 Mar-10-2017
Re: MT STAINLESS
In Reply to Ulf Hansen at 23:04 Jan-25-2012 .

Hi Ulf,

We made MT on Duplex 2209 plates, and it´s the same, you can´t see nothing...for me, the MT test shouldn´t be applied on Duplex SS...it doesn´t matter if they are castings or not.

Regards

César

 
 Reply 
 
MPI Guru
MPI Guru
08:15 Mar-10-2017
Re: MT STAINLESS
In Reply to Cesar Tovar at 08:07 Mar-10-2017 .

Just use a castrol/ely strip.

If you see the lines, go for it.

 
 Reply 
 
Chris Edwards
Consultant,
United Kingdom, Joined Dec 2012, 43

Chris Edwards

Consultant,
United Kingdom,
Joined Dec 2012
43
09:20 Mar-14-2017
Re: MT STAINLESS
In Reply to MPI Guru at 08:15 Mar-10-2017 .

Castrol strips are not reliable. They respond to the applied field (H) above the component - not the internal B field. For example if you use current flow on a steel rod (magnetic) or the same current through an aluminium rod the H field will be the same. Castrol strip will give indication in both cases. Similarly a Castrol strip will give an indication with an AC yoke or permanent magnet on aluminum or a piece of wood. The material must be magnetic and in practice the maximum field that can be used is limited by surface roughness (spurious indications masking cracks) In duplex with a coarse microstructure indications between ferritic and austenitc grains will also give spurious indications and can mask cracks.
With single phase stainless this should not be a problem problem can be very low permeablity >10.

 
 Reply 
 

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