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Technical Discussions
Mike Leger
Mike Leger
02:17 Dec-12-2001
MT Through Paint

I am interested in any qualification activities or information regarding magnetic particle testing through paint. We have a particular application where coating removal is costly and difficult. We are considering manufacturing a standard with EDM notches. Any experience?

Mike Leger
Diablo Canyon Power Plant


    
 
 
David Hermanutz
Consultant,
Hbndt.com, China, Joined Jul 2012, 85

David Hermanutz

Consultant,
Hbndt.com,
China,
Joined Jul 2012
85
06:56 Dec-12-2001
Re: MT Through Paint
: I am interested in any qualification activities or information regarding magnetic particle testing through paint. We have a particular application where coating removal is costly and difficult. We are considering manufacturing a standard with EDM notches. Any experience?
.
: Mike Leger
: Diablo Canyon Power Plant
.
Dear Mike,

The idea of testing through paint is a bit of an issue depending on which regulation authority that is governing your equipment.

Most codes state that MT cannot be done through paint "."

A special prcedure may be developed by a Level 3 MT technician that may be acceptable outside of these realms.

Some key areas to look into:

Maximum thickness of coating (typically most bridge, crane and refinery coatings far exceed what is possible with MT )

Coating material must also be 100% non-ferromagnetic

Coating thickness must be tested in all areas wher MT is to occur. Coating is often much thicker in corners where undercut / cracking is most likely to occur.

Minimum Defect size required.

EDM samples will often be much easier to detect with MT than a real crack. ( EDM are straight narrow and you know where they are vs Cracks which are small crooked and in all sort,s of locations )


There are several advanced testing systems that use electrical test methods that could be used instead of MT testing, although they would also have the same qualification difficulties with teh EDM vs real crack specimens.

Eddy Current testing has been adopted into code in the North Sea due to the harsh testing environment. This method is quite effective if the Technician is experienced and trained on eddy current weld testing.

Please feel free to contact PCN or The Welding Institute on their website for this document.

Best Regards,

David Hermanutz
Panametrics Melbourne


    
 
 
Martin Lugg
Consultant,
United Kingdom, Joined Nov 2000, 27

Martin Lugg

Consultant,
United Kingdom,
Joined Nov 2000
27
02:21 Dec-12-2001
Re: MT Through Paint
: : I am interested in any qualification activities or information regarding magnetic particle testing through paint. We have a particular application where coating removal is costly and difficult. We are considering manufacturing a standard with EDM notches. Any experience?
: .
: : Mike Leger
: : Diablo Canyon Power Plant
: .
: Dear Mike,
.
: The idea of testing through paint is a bit of an issue depending on which regulation authority that is governing your equipment.
.
: Most codes state that MT cannot be done through paint "."
.
: A special prcedure may be developed by a Level 3 MT technician that may be acceptable outside of these realms.
.
: Some key areas to look into:
.
: Maximum thickness of coating (typically most bridge, crane and refinery coatings far exceed what is possible with MT )
.
: Coating material must also be 100% non-ferromagnetic
.
: Coating thickness must be tested in all areas wher MT is to occur. Coating is often much thicker in corners where undercut / cracking is most likely to occur.
.
: Minimum Defect size required.
.
: EDM samples will often be much easier to detect with MT than a real crack. ( EDM are straight narrow and you know where they are vs Cracks which are small crooked and in all sort,s of locations )
.
:
: There are several advanced testing systems that use electrical test methods that could be used instead of MT testing, although they would also have the same qualification difficulties with teh EDM vs real crack specimens.
.
: Eddy Current testing has been adopted into code in the North Sea due to the harsh testing environment. This method is quite effective if the Technician is experienced and trained on eddy current weld testing.
.
: Please feel free to contact PCN or The Welding Institute on their website for this document.
.
: Best Regards,
.
: David Hermanutz
: Panametrics Melbourne
.
Uniform Field electromagnetic techniques, such as ACFM, are even better for this application. The use of a uniform field allows them to work through thicker coatings than conventional eddy current techniques, and also allows the magnetic field to be modelled so that depth sizing does not rely on comparison with slots in calibration blocks.

ACFM is now widely used on painted or coated structures, particularly on welded steel, and for underwater inspection.




    
 
 
Dent McIntyre
Consultant, NDE Manager NDELevel III/3
NDT Consultant, Canada, Joined Nov 1998, 247

Dent McIntyre

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
247
07:02 Dec-12-2001
Re: MT Through Paint
ASME Code (2001 edition) Section V Article 7, Mandatory Appendix 1 gives the detailed rules on performing MT through coatings such as paint.
In summary you must demonstrate the procedure with the known thickness of coating and then you must prove that the thickness of the coating on the part is the same as has been demonstrated.
Yoke lifting power must be proven through the coating as well.


    
 
 
Phil Herman Jr.
Sales, - Manufacture of NDT Reference Standards/Test Blocks
PH Tool Reference Standards, USA, Joined Oct 1999, 79

Phil Herman Jr.

Sales, - Manufacture of NDT Reference Standards/Test Blocks
PH Tool Reference Standards,
USA,
Joined Oct 1999
79
01:35 Dec-12-2001
Re: MT Through Paint
Mike,
PH Tool Reference Standards has made Magnetic Particle Inspection standards containing EDM notches for Navy customers who have painted them after our EDM work. The notches should be extremely narrow (.0015-.003") to best simulate real cracks and should be epoxy-filled to prevent mechanical holding. The epoxy is applied after EDM and before painting. You can specify any notch length, depth, orientation, and location you prefer. Hope this helps. We are happy to help or further advise if needed.
Best Regards,
Phil Herman Jr.
PH Tool Reference Standards

: I am interested in any qualification activities or information regarding magnetic particle testing through paint. We have a particular application where coating removal is costly and difficult. We are considering manufacturing a standard with EDM notches. Any experience?
.
: Mike Leger
: Diablo Canyon Power Plant
.



    
 
 
John Hansen
Director, - Eddy Current Technology
ETher NDE Ltd, United Kingdom, Joined Oct 1999, 72

John Hansen

Director, - Eddy Current Technology
ETher NDE Ltd,
United Kingdom,
Joined Oct 1999
72
03:21 Dec-14-2001
Re: MT Through Paint
Eddy current using the Hocking NDT WeldScan probe is used widely here in Europe to replace MT (MPI) when testing welds through paint and other coatings (aluminium, zinc etc).

The standard test block has shims to simulate up to 2mm of paint but in tests we have done the coating thickness can be very much greater.

There is a European Standard EN BS 1711:2000 detailing this test method.



    
 
 

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