Basic principles of non-destructive testing

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• Basic principles of non-destructive testing (NDT)
• Definition and importance of NDT
• Non-destructive testing is the use of
  physical methods which will test materials,
  components and assemblies for flaws in their
  structure without damaging their future
  usefulness. NDT is concerned with revealing
  flaws in the structure of a product. It, however,
  cannot predict where flaws will develop due to
  the design itself.
• All NDT methods have the following common
  characteristics
• The application of a testing medium to the
  product to be tested.
• The changes in the testing medium due to the
  defects in the structure of the product.
• A means by which it detects these changes.
• Interpretation of these changes to obtain
  information about the flaws in the
  structure of the product.

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Magnetic Particle Testing (MPT)- Magnetic
Particle Testing is also known as magnetic
particle Inspection (MPI). Magnetic particle
Inspection (MPI) is a non-destructive
testing (NDT) process for detecting surface
and slightly subsurface discontinuities in
ferromagnetic materials such as nickel, iron,
cobalt, and some of their alloys. The process
puts a magnetic field into the part. The piece
can be magnetized by direct or indirect
magnetization. Direct magnetization occurs
when the electric current is passed through
the test object and a magnetic field is
formed in the material. Indirect magnetization
occurs when no electric current is passed through
the test object, but a magnetic field is applied
from an outside source. The magnetic lines of
force are perpendicular to the direction of
the electric current, which may be either
alternating current (AC) or some form of direct
current (DC) (rectified AC). Non-Destructive
Testing for MPT The presence of a surface
or subsurface discontinuity in the material
allows the magnetic flux to leak, since air
cannot support as much magnetic field per unit
volume as metals. A wet horizontal MPI machine is
the most commonly used mass-production inspection
machine. This requires special equipment
that works the opposite way of the
magnetizing equipment. The magnetization is
normally done with a high current pulse that
reaches a peak current very quickly and
instantaneously turns off leaving the part
magnetized. To demagnetize a part, the
current or magnetic field needed has to be
equal to or greater than the current or
magnetic field used to magnetize the
part This course contains Level 1 and 2 study
material from NDT Consultancy Services and
covers the theory of Magnetic Particle
Examination. Magnetic fields, flux leakage,
magnetization processes, particles/mediums,
applications, basic principles, and safety
considerations are addressed. This 24-hour
course exceeds the instruction outline
and criteria specified in the ASNT
Recommended Practice SNT-TC-1A and ASNT
Standard Topical Outlines for Qualification
of Nondestructive Testing.