INTRODUCTION
TO MAGNETIC PARTICLES TESTING (MT)
Introduction to Magnetic Particles Testing
Objectives of Magnetic Particles Testing
Theory of Magnetic Particles Testing
Training & Certification
Introduction to UT
Because magnetization of certain metals is possible. It
is possible to reveal discontinuities by using a medium
iron powder having magnetic attraction.
The medium is applied to the surface of the test object
after or during induction of a magnetic field.
The sketch below shows a buildup of the magnetic particle
medium over the discontinuity in the magnetized part.
Magnetic particle testing is a relatively easy and simple
test method that can be applied at various stages of manufacture
and processing operations.
Objectives of Magnetic Particles Testing
The objective of magnetic particle testing is to insure
product reliability by providing means of :
A). Obtaining
a visual image of an indication on the surface of a material.
B). Disclosing the nature of discontinuities without impairing
the material.
C). Separating acceptable and unacceptable material in
accordance with predetermined standards.
Theory of Magnetization
An object is magnetized when part or all of its magnetic
domains have their north and south poles oriented.
The ability of magnet to attract or repel is concentrated
at the local areas called poles the north and south poles
exhibit attraction and repulsion.
With all of the magnetic domains lined up, the magnetic
bar develops a total force equal to the sum of all of the
magnetic domains.
These are the magnetic lines of force which form a closed
loop or circuit.
All the lines of force take up the magnetic field.
Training & Certification
It is recognised that the effectiveness of nondestructive
testing depends on the capabilities of the personnel who
are responsible for, and perform NDT. Thus all customers
will require an assurance that NDT personnel whose specific
jobs require appropriate knowledge of the technical principles
underlying the nondestructive tests they perform, witness,
monitor, or evaluate be qualified and certified. In addition
every country may also have a program of training &
certifying personnel responsible for performing radiography
be qualified & certifies in safety aspects related use
of radiation sources.
The American Society for Nondestructive Testing recommends
the use of the documents “recommended practice no.
SNT-TC-1A”. This document provides
the employer with the necessary guidelines to properly qualify
and certify the NDT technician in all methods. To comply
with this document the employer must establish a “written
practice” which describes in detail how the technician
will be trained, examined and certified.
Current edition of SNT-TC-1A may be referred
to determine the recommended number of hours of classroom
instruction and months of experience necessary to be certified
as a radiographic testing technician. Certification of NDT
personnel always rests with the employer and is usually
at three levels.
Level I - is qualified to perform specific
calibrations, specific tests, and specific evaluations.
Level II - is qualified to set up and
calibrate equipment and to interpret and evaluate results
with respect to codes, standards and specifications. Must
be able to prepare written instructions and report test
results.
Level III - must be capable and responsible
for establishing techniques, interpreting codes, and designating
the test methods and techniques to be used . Must have a
practical background in the technology and be familiar with
other commonly used methods of NDT.
The SNT-TC-1A document recommends that
level I and level II NDT technicians be examined in the
following areas:
A. General examination.
B. Specific examination.
C. Practical examination.
The SNT-TC-1A document recommends that
NDT level III personnel be examined in the following areas:
A. Basic examination.
B. Method examination.
C. Specific examination.
NDT
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