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3529 views
14:28 Feb-12-2009
Jean-Claude Schwartz
MT on manganese

Hello,

I have a client who is welding large steel plates. The weld is a mild carbon steel, however the parent plates contain 18% magnesium. Normally magnesium cannot be tested by MT, however with only 18% magnesium I am getting a very good pull from the electromagnetic yoke. The burmah castrol strip pulls up and I am obtaining a field according to the flux meter. A constant temperature of 100°C must be maintained therefore I cannot use PT (unless somebody knows of a penetrant suitable at 100°C?)
Does anybody know if this is still an acceptable means of testing?

 
15:49 Feb-12-2009

Godfrey Hands

Engineering,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
284
Re: MT on manganese In Reply to Jean-Claude Schwartz at 14:28 Feb-12-2009 (Opening).

Hi,
Magnesium is a light alloy and cannot be MT inspected.
However, MANGANESE Steels (depending on their other alloying comstituents and concentrations) can be.
The important question is "Does a magnet stick on the surface?"

Godfrey

 
16:23 Feb-12-2009

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1094
Re: MT on manganese In Reply to Jean-Claude Schwartz at 14:28 Feb-12-2009 (Opening).

Jean-Claude


Chemetall (formerly Ely) Checkmor C colour-contrast penetrant has a 200 deg Celsius Flashpoint so could be used in combination with SC remover and LD 2(M) developer.

Like Godfrey I wonder if you have Mn = Manganese and Mg = Magnesium inverted. If it is high magnesium I wonder which welding process and safety precautions were used to prevent a fire starting?

 
16:50 Feb-12-2009

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
158
Re: MT on manganese I don't think there is such an alloy as steel with 18% magnesium. 18% manganses steel is ferromagnetic and can be tested by the magnetic particle method.
 
12:37 Feb-13-2009

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
Re: MT on manganese In Reply to John Brunk at 16:50 Feb-12-2009 .

Dear Sir,

You are right that there is no steel with 18% Magnesium. Magnesium cannot be alloyed with Fe. As you have pointed out, there are steels with 18% Mn. When the Manganese content exceeds about 12% the steel tends to be Austenitic. As you are very much aware, the Austenitic steels are weekly magnetic and cannot be subjected to MT. But there is a catch.

"THE ORIGINAL AUSTENITIC MANGANESE STEEL, containing about 1.2% C and 12% Mn, was invented by Sir Robert Hadfield in 1882. Hadfield's steel was unique in that it combined high toughness and ductility with high work hardening capacity and, usually, good resistance to wear."

The Hadfield steels are highly amenable to work hardening. When they are subjected to work hardening they undergo a transformation to martensitic phase (near the surface) which is very much ferromagnetic and the part can be subjected to MT. The work hardening is done by impacting or light hammering or during service (the points and frogs in railway tracks). Any part made of this steel, if subjected to even minor work hardening, is bound to develop these magnetic properties to various degrees and certainly the Electromagnetic Yoke sticks.

However the transformation to martensitic phase is very much non-homogenous and to that extent the ferromagnetic field is also non-homogenous and this can be tricky during the MT. The exceptions are when the part is uniformly work hardened like ring forging or cold rolling without further heat treatment, in which case the MT can be happily carried out.

P V SASTRY

 
13:27 Feb-13-2009

Dent

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
246
Re: MT on manganese In Reply to Godfrey Hands at 15:49 Feb-12-2009 .

ASME Sect V Article 7 par T-764.3 does not allow the use of magnetic field indicators or artificial flaw shims when using the yoke technique.

Try putting your yoke on a piece of wood and use these tools.
Bingo you show a field.
But do you think you can test the wood? Of course not.

The test here is if the yoke will lift 10 ( for AC) or 40 pounds (for DC) of this material at the pole spacing you plan to use then you can properly test the material.

 
08:29 Feb-14-2009
Navita Gupta
Re: MT on manganese In Reply to Dent at 13:27 Feb-13-2009 .

I fully agree with Dent. Since a yoke generates longitudinal magnetic field, the only way we can check appropriate magnetisation is by the weight lift test. Due to the closed nature of magnetic lines of force, the field indicator picks up the direction of magnetic field and NOT the magnetic field in the material being tested. Similarly, since a shim has a known discontinuity , it is picked up by the magnetic field. It no way proves that magnetic lines are travelling in the material being tested.
Navita

 
18:08 Feb-14-2009

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
806
Re: MT on manganese In Reply to Navita Gupta at 08:29 Feb-14-2009 .

Hi Gents,

For one thing, I got to say that I learned something here. It never occured to me of making the 10 lbs and 40 lbs weight in the material that I would be testing, which really make sense, but in this situation, I do have some reservation. P V Sastry stated that the ferromagnetic properties of the material are not homogeneous throughout, so how will one be sure of the inspection being carried out?

Very little details is given about the material except that it is a weld at 100 degrre Celcius. I remember years ago when I was doing my Eddy Current exam, I had to inspect a small plate of Austenetic Stainless Steel and I was having a hard time until I use a differential coil probe. Maybe it is the way to go! Or since it is a weld, why can't good old UT be used? In this case, you may have to use a 0.5 or a 1 MHz transducer and some High Temp couplant.

 
17:37 Feb-16-2009

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
Re: MT on manganese In Reply to Michel Couture at 18:08 Feb-14-2009 .

Without a surface-wave 'ducer, UT is terrible for surface defects. Sherwin makes a Hi-Temp visible dye PT kit, with a foam cleaner. Works well. Passes Nuclear performance demonstration testing.

The MT would be MUCH faster, and what I'd use. Just use a weight scale to check 'pull' weight at random [but often] intervals. Remember to 'tare' off the weight of your yoke.

 


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