MPI

[Sam Rutherford]

Hi all,

What's the word on this inspection?

How often, and what sort of cost should it come in at (assuming no problems found)?

Thanks, Sam.

[a64pilot]

Sam,
I'm completely at a loss, what's MPI?

[Sam Rutherford]

Magnetic Particle Inspection - non-destructive testing of the steel frame of the aircraft...

Sam.

[Skystrider]

Just when I thought I knew it all, up comes MPI!

[210TC]

Never heard of this requirement on an airframe. However, Robinson Helicopters does conduct this test on landing assembles, engine and gear box mounts before powder coating at overhaul. All of the steel mounts.
Most airframes are 4130 chrome molly and seldom crack. This does not mean they never crack as they sometimes do around gussets in the landing gear area after 40 to 60 years.
I always inspect high stress point areas during each annual. If I find rust or paint crinkled that doesn't look right I get out the magnifying glass first, never had to do dye or particle inspection. BUT, I don't know everything and I sure haven't seen everything.
I may be wrong about Robinson, they do test. However, it could be a different type of test??? The test your talking about uses a magnet that is placed on the area to be checked and some special power is blown on with a small hand held squeeze bottle between the horse shoe points of the magnet. If a crack is present it will show it clearly. When you take an old steel/cast iron cylinder head to the machine shop this is how they check for cracks.

[a64pilot]

OK, I know about Mag Particle, what are you inspecting? Crankshaft or something?

[210TC]

This is good

http://www.ndt-ed.org/EducationResource ... rtable.htm

[a64pilot]

I'm still wondering what he wants to mag particle. If he is trying to inspect the airframe I would suggest filling it with linseed oil and draining it. Trust me any crack will become immedately apparent, it also almost absolutely prevents any corrosion from the inside of the tubes.
All Thrush airframes are completely filled with hot linseed oil and drained for this purpose. Twenty years later if an airframe cracks, you know it because it looks as if varnish is leaking from an otherwise invisable crack.
As an inspection procedure of a steel part, eddy current is superior to mag particle, but neither is warrantied for a Maule airframe in my opinion, except maybe where there is suspicion of damage, like maybe if you hit so hard as to spread the gear, the attach points may be looked at.

[belandd]

I like the idea of using linseed oil. However it is a bit awkward trying to make sure you get all of the tubes seviced.

On some of the helicopters I maintain the steel tubing is pressurized with a gage attached. When the pressure on the gage drops then you know you have a leak.

Merry Christmas!

[belandd]

AC 43-13-1B requires that steel tubing be inspected with an ice pick!

If the ice pick penetrates the tubing then it fails the inspection.

I have found bad tubing this way. The most recent was on a Stinson and the tubing was under the seat where the main gear attaches.

Kind of crude but simple and cheap!