4 - Prong -Yoke on M.P.I test.

[ibf]

Hello All !

Is it acceptable as per ANSI/ASNT Standards to use a 4 - prong - yoke to develop magnectic particle test on castings ? If "yes" or "no" , could you explain why ? We saw that for the first time in China , and confess that I had a hard time to follow the magnectic field created by the 4 prongs simultaneously.

Thank you.

 

[metengr]

Are you sure that all four of the yolk prongs were energized simultaneously during the magnetic particle test?

It could be that they alternate between two prongs in 90 degree directions to assure complete coverage. This would be no different than using a set of prods and rotating them 90 degrees between tests to check for defects that could be of different orientation.

 

[Kenneth]

I had heard of so-called "simultaneous" (circular and longitudinal) magnetic particle machines:

from

http://www.americanndtinc.com/product_pages/mpi3dp2.htm

"In reality, two or three magnetic fields cannot be imposed on a part simultaneously. The result would be a "washed out" vector average of the three fields. In "3D" mode, the fields are imposed 60° out of phase so that the magnetic domains inside the test part rapidly switch magnetization directions as the modes are switched. The magnetic particles forming the observable indications on the part's surface, however, do not have time to react to the rapid switching, so the "3D" mode gives the appearance of simultaneous magnetization in three directions."

Could the four-prong set-up possibly be something similar?

 

[ibf]

Thanks metengr and Kenneth.

Yes, the four of them were energized at the same time, and the fields were diagonally opposed. Anyway , I will take your answers as a "not possible" or maybe "not usual" (?).

 

[metengr]

ibf;
I would say not typical. However, to track this down even further, I would request a copy of their NDT procedure and practice to determine if they are even qualified. As a minimum, their procedure for magnetic particle examination should conform to ASTM E-709, and they should have a written practice similar to ASNT TC1A. As part of the procedure qualification under ASTM E-709, there are detailed essential variables that need to be evaluated.

As a follow-up, Article 7 in Section V of the ASME B&PV Code addresses the use of multidirectional magnetic fields. To produce these fields, high amperage power packs (typically 3) all are energized at one time, but in rapid succession. The rapid alternating magnetizing currents results in overall magnetization of the part in multiple directions.

 

[ibf]

Understood metengr , and thank you very much for the additional input.

Regarding the procedures, "yes" , we did receive them prior to commencing the job and believe me , they were i.a.w ASTM E-709 ; HOWEVER, THEY HAVE NEVER MENTIONED the use of multiple fields at all before !!

I will check ASME SEC V.

Thank you.

ibf