A brief explanation of MPI w/pics

ASH556 · #1 03-05-12, 10:22

My day job is as an applications engineer for a valve company. Most of what I do is with high pressure/high temp applications for power plants (steam service). Due to the critical nature of the process contained in these vessels, there are several safety and manufacturing codes that must be complied with. One of these is MPI.

I was recently at a valve manufacturer's facility and in their QC department they demonstrated an MPI for us. To the naked eye, the valve body looked as solid as could be. However, they sprinkled the valve with red ferrous (magnetic) dust. They then used electrofied probes to create a magnetic field across the valve. The dust accumulated in the flaws and they became clear, thus the valve body was scrapped. As you can imagine, you'd want to similarly find flaws in the constructions of the critical pressure-containing parts of a firearm like an AR15. Thus, the reason for and importance of quality MPI bolt and barrel:

Kokopelli · #2 03-05-12, 10:27

Good post.. Most people don't have a reference for this type of testing.. Cheers.. Ron

meganeura · #3 03-05-12, 11:01

Interesting post.

What am I looking at exactly? I see a rust-colored meandering line which is presumably the crack detected by MPI. Is the meandering white line related?

ASH556 · #4 03-05-12, 11:06

Quote:

Originally Posted by meganeura

Interesting post.

What am I looking at exactly? I see a rust-colored meandering line which is presumably the crack detected by MPI. Is the meandering white line related?

The red line is the detected flaw. The "white line" is camera flash.

ICANHITHIMMAN · #5 03-05-12, 11:07

Thats cool. I am a welder and have seen xray but never this very cool.

meganeura · #6 03-05-12, 11:12

Quote:

Originally Posted by ASH556

The red line is the detected flaw. The "white line" is camera flash.

Neat stuff. Thanks for the response. I've seen some pictures of the process where a UV-fluorescent dye is used to pick out the flaws

ForTehNguyen · #7 03-05-12, 12:51

what is the valve body manufacturing process, forged or casted? If its for high pressure steam im gonna lean towards forged. Curious about the valve size too

maddawg5777 · #8 03-05-12, 12:56

This should be stickied for new users unfamiliar with mpi so they can get a visual of the testing done and why its important.

Frens · #9 03-05-12, 13:14

wow interesting, thanks for sharing!

ASH556 · #10 03-05-12, 13:15

Quote:

Originally Posted by ForTehNguyen

what is the valve body manufacturing process, forged or casted? If its for high pressure steam im gonna lean towards forged. Curious about the valve size too

I don't remember exactly, but I want to say it was a 12" ANSI 1500 A105 (forged carbon steel). It was a parallel disc gate valve.

Moltke · #11 03-05-12, 13:24

Thanks for posting this.

FSTRN · #12 03-06-12, 00:13

Yes, thank you. The visual aid really helps.

zibby43 · #13 03-06-12, 01:18

Quote:

Originally Posted by maddawg5777

This should be stickied for new users unfamiliar with mpi so they can get a visual of the testing done and why its important.

I second that motion.

big b · #14 03-06-12, 03:19

Interesting. Thanks for taking the time to put this up.

BufordTJustice · #15 03-06-12, 05:47

Quote:

Originally Posted by zibby43

I second that motion.

I'll third it. Outstanding post with an excellent pic.

meganeura · #16 03-06-12, 11:00

I would love to see actual MPI pictures of an M16/AR15 barrel and bolt.

Does anyone have any of those to share?

hotrodder636 · #17 03-06-12, 11:12

Quote:

Originally Posted by meganeura

Neat stuff. Thanks for the response. I've seen some pictures of the process where a UV-fluorescent dye is used to pick out the flaws

The test you are referring to is a Dye Penetration Test....used for doing similar identifying of issues as MPI. Used a lot on piping at power-houses. Working at nuclear power plant, I have seen/get to see/read about some pretty intense NDT on various materials as well as DT.

CumbiaDude · #18 03-07-12, 00:34

Too bad there was no before pic, but then how would you know to take a pic of something you haven't seen there?

Cool stuff, tho!

Dsm2nr · #19 03-07-12, 00:55

MP is used in a lot of things.

Here's a couple good videos for anyone wanting to see it done:

Skip to 0:51
http://www.youtube.com/watch?v=0o1Us...eature=related

Skip to 1:18
http://www.youtube.com/watch?v=V0R5GVCxBy4

Spectro · #20 03-07-12, 01:13

Good to see a post like this. No hijack intended, but years ago me and a colleague worked many hours developing techniques for photographing both MPI and LPI fluorescent indications in many different types of components using Ektachrome slide film. Oops, I just aged myself didn't I.

Wet Fluorescent MPI can be much more sensitive compared to the dry powder method and is the preferred method when testing critical components. This is due to the smaller size and uniformity of the particles used and the ease of applying the particles (in suspension) to the test part.

Here is a pic of a raw cast steel valve that obviously failed a WFMPI examination.