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Technical Discussions
YONGOH SHIN
YONGOH SHIN
04:12 Feb-27-2002
Reliability of MT

When threaded fasteners, bolts, are inspected for circumferentail discontinuities in accordance with coil magnetization current formulas such as in MIL-STD-1949, nonrelevant indications in thread roots due to magnetic saturation are commonly obserbed. Recently, owing to continuous development of magnetic particle testing, a very small size crack can be detected by minimizing the magnetic field distortions.
Could anyone tell me the minimum crack size, length and depth, in the bolt roots to be detected by applying the advanced MT technology?
Could anyone inform me the relevant reports or your experiences about the above issues?
Thank you.


    
 
 
Dave Wilkes
Dave Wilkes
08:31 Feb-27-2002
Re: Reliability of MT
Could you tell us which advanced MT Technology you
are referring to ? What is the system called ?




    
 
 
Yongoh Shin
Yongoh Shin
03:50 Feb-27-2002
Re: Reliability of MT
It doesn't mean the specialized method.
In order to inspect flaws in bolt roots we have to use more sensitive MT equipment and material such as wet flourscent, more fine particle, and better lighting etc.
Anyway, I want to know more specific sensitivity of MPI.
What is the minimum crack size MPI can detect a flaw in steel bolt roots.
Please send me relevant reports or information if you have.

Sincerely,

Yongoh Shin
AEI ltd. in Calgary



    
 
 
Bill Cook
Bill Cook
01:42 Feb-28-2002
Re: Reliability of MT
: It doesn't mean the specialized method.
: In order to inspect flaws in bolt roots we have to use more sensitive MT equipment and material such as wet flourscent, more fine particle, and better lighting etc.
: Anyway, I want to know more specific sensitivity of MPI.
: What is the minimum crack size MPI can detect a flaw in steel bolt roots.

That will vary with the following:

Type of magnetizing current.
Strength of field.
Magnetic properties of the bolts.
Size of bolts
Thread characteristics (depth and type)

There is no "hard and fast" rule for minimum flaw size detectable.

Bill



    
 
 
N.T.Azarov
Engineering
GosNIIGA, Russia, Joined Jan 2000, 12

N.T.Azarov

Engineering
GosNIIGA,
Russia,
Joined Jan 2000
12
04:07 Feb-28-2002
Re: Reliability of MT
: It doesn't mean the specialized method.
: In order to inspect flaws in bolt roots we have to use more sensitive MT equipment and material such as wet flourscent, more fine particle, and better lighting etc.
: Anyway, I want to know more specific sensitivity of MPI.
: What is the minimum crack size MPI can detect a flaw in steel bolt roots.
: Please send me relevant reports or information if you have.
.
: Sincerely,
.
: Yongoh Shin
: AEI ltd. in Calgary
.


We have durablis (from 1995) experiences ultrasonic and magnetic (flouroscent) control of fatigue cracks in bolts by a diameter 16-18mm and length up to 100mm, used in aircraft. The reliability of detection of cracks in a t h r e a d by a magnetic method less than 50 %, ultrasonic - 80-90%.Is installed, that depth of detected cracks more 1mm, length 8-10mm.
N.T.Azarov.


    
 
 
Dave Wilkes
Dave Wilkes
08:39 Feb-28-2002
Re: Reliability of MT
As Bill Cook say's there is no "hard and fast" rule for minimum flaw size detectable.

Interpreting the indications produced by MT in bolt
roots is very, very difficult.

The minimum size that is detectable in a controlled
laboratory test is very different to that found in
the production environment.

We recently discussed the pro's and con's of testing
with both the 'Fluorescent' and 'Black on White'
MT methods and you might find the comments in that
article useful.

Fluorescent MPI - Is it really necessary ?

http://www.ndtcabin.com/fluor_mpi_upd.asp

Dave Wilkes



    
 
 

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