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Hillger NDT GmbH
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Technical Discussions
Jonathon Wilson
Jonathon Wilson
20:32 Aug-17-2017
MPI on small compression spring
zoom image



The attached picture is of the part that requires MPI. The spring itself is relatively small, I can get exact measurements, but I'm talking ~2 in in length. The material itself is very thin as well. Unfortunately for me, the specification doesn't call out a secondary inspection so we're left with this or purchase entirely new parts every time we overhaul a unit. Even if I were to cut a shim down to size, I still can't reliably use that method to verify a process has been properly created. Using a hall effect meter and a central bar method I can get ~35-55g at 100A, but getting a measurement within the coil is impossible. If I compress the spring between the head and tail stocks using the small parts adaptor I run into the issue of arcing so that seems to be ruled out.

So ultimately, my question would be... Has anybody run into a similar situation or have any ideas for a way to perform MPI on this?

 
 Reply 
 
Diego
Consultant,
Freelance, Spain, Joined May 2013, 188

Diego

Consultant,
Freelance,
Spain,
Joined May 2013
188
21:42 Aug-17-2017
Re: MPI on small compression spring
In Reply to Jonathon Wilson at 20:32 Aug-17-2017 (Opening).

Mr. Wilson
In my opinion, a circular direct magnetization technique using AC continuous could be used with good results. See ASTM E709.
Regards

 
 Reply 
 
Rick Lopez
R & D,
John Deere - Moline Technology Innovation Center, USA, Joined Jul 2011, 189

Rick Lopez

R & D,
John Deere - Moline Technology Innovation Center,
USA,
Joined Jul 2011
189
22:13 Aug-17-2017
Re: MPI on small compression spring
In Reply to Jonathon Wilson at 20:32 Aug-17-2017 (Opening).

I have not run into this type of application - that looks like a challenge. It would seem (in my mind) that head-shot and coil shot would essentially be equivalent for this part. You'd likely be seeking fatigue cracking that is transverse to the wire. Coil magnetic field would roughly be parallel to such a flaw. A head shot (maybe done by clamping contacts to the ends of the coil) would set up a circular field around the wire, and this also would also be approximately parallel to the expected flaw. Aside from post-emulsified fluorescent penetrant (you'll have trouble cleaning penetrant from the end areas where coils touch - maybe a temporary toothpick opening the gap would help), I would think your internal/central conductor is the best setup. This field orientation should be roughly perpendicular to flaws, and be most sensitive...but then, how to inspect the inside diameter, and all orientations/areas on the wire. All of that aside, in the few fatigue-fractured springs I've seen, there was very little crack propagation after initiation - in other words, they tended to break quickly once an NDT-detectable flaw had initiated. This might be a bad assumption, but I would guess that the likelihood of finding a cracked one that had not yet fractured might be pretty slim.

 
 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
22:37 Aug-18-2017
Re: MPI on small compression spring
In Reply to Jonathon Wilson at 20:32 Aug-17-2017 (Opening).


I have seen the picture of the spring and somewhat understood your problem.

It should be possible to perform an effective Magnetic Particle testing on this.

Before that, I need to know the following information.

How many nos. have to be inspected in a day or week etc.

What is the material and dia. of the wire used in making the spring.

Any other information regarding the manufacturing of the springs, like whether the wire is directly purchased or drawn in the works of the manufacturer etc.

What kind of defects you were physically observing in new and/or used springs and what is rejection criteria.

Can you send me one new or rejected spring to enable me make the suitable jig for MPI.

If you please give the above information (even partially) probably a suitable method can be developed.

Best wishes

P V SASTRY

 
 Reply 
 
George Hopman
Consultant,
NDE Solutions, USA, Joined Apr 2009, 44

George Hopman

Consultant,
NDE Solutions,
USA,
Joined Apr 2009
44
16:54 Aug-21-2017
Re: MPI on small compression spring
In Reply to Diego at 21:42 Aug-17-2017 .

This is relatively easy inspection IF you have the right equipment. I have seen this done before. First you need the proper magnetizing unit. Magwerks out of Indianapolis sells many models that have an "Ultra-low Range" option. The inspector can have amperage as low as 10 amps with one amp resolution. Therefore, one will not burn the small diameter component of the spring.

Second, one must have what I call a "External Cable Adaptor". This is a block of wood (2 x 4) covered with copper on the 1.5" side (3 sides). This fixture allows a cable to be attached to the fixture. Instead of a cable, attach a small diameter wire with an alligator clamp on the two ends. Clip the alligator clamp to each end of the spring. This will provide direct circular magnetism to the spring. Use a HE gaussmeter to determine the proper amperage.

For the opposing magnetism, use a central bar conductor and the HE gaussmeter for proper amperage determination.

Thanks!

 
 Reply 
 
Peter P.
Consultant, ASNT MT/PT Level 3, Quality Manager
SharingNDT, USA, Joined Jan 2017, 80

Peter P.

Consultant, ASNT MT/PT Level 3, Quality Manager
SharingNDT,
USA,
Joined Jan 2017
80
00:04 Aug-31-2017
Re: MPI on small compression spring
In Reply to Jonathon Wilson at 20:32 Aug-17-2017 (Opening).

Anytime I ran into a part this small I would either

a) use a small parts adapter on the MT machine: http://ow.ly/19Fz30eNzIR

b) make a V-groove trolley out of a conductive material to clamp between the heads; this will allow you to place the part inside and allow the excess mag fluid to drain off.

c) get some electrical (non-conductive tips) needle nose pliers.

I wouldn't make it complicated.

- Peter

 
 Reply 
 
George Hopman
Consultant,
NDE Solutions, USA, Joined Apr 2009, 44

George Hopman

Consultant,
NDE Solutions,
USA,
Joined Apr 2009
44
00:20 Sep-01-2017
Re: MPI on small compression spring
In Reply to Peter P. at 00:04 Aug-31-2017 .

I am not sure what specification or code you are working to. I love MET-L-CHEK, but Peter's suggestion to use a V channel is a classic case of "parallel magnetism". It it disallowed in ASTM E1444/E1444M, The ASNT NDT Handbook, Betz's Principles of Magnetic Particle Inspection, and TO-33B-1-1.

Parallel magnetism introduces two different fields into the part, not just one circular field. Thanks!

1
 
 Reply 
 
Peter P.
Consultant, ASNT MT/PT Level 3, Quality Manager
SharingNDT, USA, Joined Jan 2017, 80

Peter P.

Consultant, ASNT MT/PT Level 3, Quality Manager
SharingNDT,
USA,
Joined Jan 2017
80
18:27 Sep-05-2017
Re: MPI on small compression spring
In Reply to George Hopman at 00:20 Sep-01-2017 .

Hey George, hope you are doing well. Because he's not mentioning any spec (1444), application (aerospace), or acceptance criteria, what else is there to say unless a very small diameter central conductor is used and/or a small part adapter is installed? If MT is the only tool available, then a transverse direction from a parallel field may be the only option.

Always a pleasure George.

 
 Reply 
 
Jonathon Wilson
Jonathon Wilson
15:33 Sep-06-2017
Re: MPI on small compression spring
In Reply to Rick Lopez at 22:13 Aug-17-2017 .

Yeah, the most I've come up with is a CBC through the center and FPI afterward. We'll have to get engineering approval and they should be fine with it since the spring is such a thin specimen that one direction of magnetism would likely detect a defect. On top of that, if it were to fail it would likely be a clean break through the entirety of the material and would be visually evident.

For the record, I work by myself at my company and run the lab with a contracted Level 3 from a different company there to assist me while I gain the necessary experience to test up to level 3. The level 3 would rather I use shims on the spring, but that's just... not possible, and my quality director wants two directions of magnetism before I send it off for approval.

 
 Reply 
 
Jonathon Wilson
Jonathon Wilson
15:54 Sep-06-2017
Re: MPI on small compression spring
In Reply to Peter P. at 00:04 Aug-31-2017 .

Sorry, I should have been more clear in my original post. I work at an MRO shop so we get numerous parts that all adhere to different specs depending on the aircraft it came off of. In this instance, though, the governing documents are 1444 and the Boeing MPI SOPM. Although I'm always willing to try different methods to magnetize a part, I'm not familiar with parallel magnetism and 1444 doesn't necessarily disallow the method, but at the same time, it doesn't allow it. I'd have to get engineering approval and would have to prove the method is sufficient enough to meet the necessary inspection requirements.

Personally, I'd rather just do one direction of magnetism with a CBC and use a hall effect meter to get a proper gauss measurement. Since it's such a thin material and the construction isn't typical, I'd imagine a defect would be easily viewable in one direction.

 
 Reply 
 
George Hopman
Consultant,
NDE Solutions, USA, Joined Apr 2009, 44

George Hopman

Consultant,
NDE Solutions,
USA,
Joined Apr 2009
44
20:36 Sep-06-2017
Re: MPI on small compression spring
In Reply to Jonathon Wilson at 15:54 Sep-06-2017 .

Paragraph 6.2.10 of E1444/E1444M disallows parallel magnetism.

I thought of an easier way; not sure why I didn't suggest it at first. First do your non-ferrous central bar shot. Second, use a steel central conductor (flux extender) that is as large as possible through the spring. Bingo. You have magnetism in two directions.

Thanks!

 
 Reply 
 
Peter P.
Consultant, ASNT MT/PT Level 3, Quality Manager
SharingNDT, USA, Joined Jan 2017, 80

Peter P.

Consultant, ASNT MT/PT Level 3, Quality Manager
SharingNDT,
USA,
Joined Jan 2017
80
22:02 Sep-08-2017
Re: MPI on small compression spring
In Reply to Jonathon Wilson at 15:54 Sep-06-2017 .

zoom image



Hey Jonathon, I uploaded what the Betz book says about parallel magnetism so you have a better understanding. ASTM E1444/E1444M, The ASNT NDT Handbook, and TO-33B-1-1 are direct quotes from the Betz book.
 
 Reply 
 
Eddy Rosales
NDT Inspector,
Canada, Joined Jan 2014, 24

Eddy Rosales

NDT Inspector,
Canada,
Joined Jan 2014
24
18:36 Sep-14-2017
Re: MPI on small compression spring
In Reply to Jonathon Wilson at 20:32 Aug-17-2017 (Opening).

I like how everyone is talking about how to MPI this part and that's great and all, you have gotten some good responses but I am starting to wonder one thing.

This is clearly something you overhaul and your manual does not say anything about NDT so your left with having to purchase a new one every time you overhaul right. I can understand you want to NDT it so you can prove its still good and put back into service right, well that's a good call be I wouldn't do that if I was you.

Just think of this, if something where to happen to this unit where the spring goes and they do an investigation lets say, they see your paper work and notice that you did not install new part they will ask why, you say because I NDT the part and it was fine, they will ask where does it say to do that ? since you don't have an answer to do that your on the hook now for this accident.

There can be multiple answers as to why your manual doesn't call for an inspection and to simply replace it, maybe they simply want to make money on selling parts or maybe its because they have noticed that this spring will not last a second overhaul. I don't mean that it will crack but there is something like a spring test and maybe they know that after the use of one overhaul the spring will not have the same strength it did when new so they simply want to replace it.

overhaul you got to ask your self are you willing to risk installing this spring when the manual does not call for NDT and re-install ?

 
 Reply 
 

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