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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.

 

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