For MT magnetic particle testing proper
lighting is important. For visible, you usually need 100 fc (foot
candle) of white light at the surface of the part that you are
inspecting. This is to assure that you can see the flaw adequately.
Many people overlook this requirement
For fluorescent testing the light requirements
are tougher. Hence, the reason most people try to accomplish
visible even if it is not appropriate. You usually have to be in a
dark area not to exceeding 2 fc (foot candle) and the black light
has to be able to produce 1200 µW/cm² (microwatts centimeter
squared) at the surface. In simple terms, you have to be in a very
dark room with a black light much stronger than what you see at a
dance club. If you do not meet these minimums, your sensitivity
will be off and you will probably miss what you are looking for.
The flipside to this statement is that your black light or white
light can be too bright and you can miss cracks because of glare,
which they can produce.
 Remember
that when we are talking about missing a crack we are referencing
the possibility of an inspector missing a crack on an airplane,
railroad wheel, fuel tank, ship hull, pipeline, etc. We are
usually talking about the possibility of people getting hurt if
the NDT Magnetic particle technician is doing their job
improperly. This is why NDT magnetic particle technicians should
be properly qualified and certified to a Level II when performing
examinations. Qualification is referencing classroom training and
experience hours. Certification is referencing that the individual
has passed a program by testing and demonstration of their
capabilities in accordance with a code such as SNT-TC-1A or
NAS-410 and has been reviewed by a Level III. Facilities are
supposed to have a primary Level III on file for code conformance.
If you do not have a Level III on file we can provide that service
for you (shameless plug # 2) and keep you code compliant.
If you are a quality assurance manager or a
company outsourcing NDT, I strongly recommend you ensure that the
facility providing your services has not reduced code
requirements. You can ensure this by requesting the personnel
records of the technician doing the work and verifying them with
the applicable standard. This is a normal practice and on request
the contractor should provide you with the information within an
hour. If they do not, you should question their services and
perhaps hire a third party ASNT Level III to provide an onsite
audit of their facility. Common mistakes found on certification
paperwork include not enough training or experience hours,
training facility and person that provided the training not
listed, and method or technique not listed.
Is magnetic particle testing the answer for your
specific method? It depends on many variables. Keep in mind that
nondestructive testing includes many different methods. In
conclusion thank you for taking the time to read our article. For
any of your nondestructive needs, we hope you consider Aqualified
LLC in the future. Feel free to e-mail or call me directly with any
questions.
Amado Garcia
a.k.a. Glen
ASNT# 125289
NAS-410 Level III PT, MT, ET, UT, RT, VT
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