INTRODUCTION
TO RADIOGRAPHIC TESTING (RT)
Introduction to Radiographic Testing
Application of Radiographic Testing
Advantages of Radiographic Testing
Limitations of Radiographic Testing
Training & Certification
Introduction to Radiographic Testing
Radiographic testing is one of the primary nondestructive
test methods widely practiced.
Application of Radiographic Testing?
Because of the penetrating ability of X and gamma (g) radiation
and absorption characteristics in materials, radiography
is used to test a variety of products such as welds, castings,
forgings, and assemblies.
Conventional radiographic testing usually requires exposing
a photographic film of specific characteristics to X or
g rays that have penetrated a specimen and processing the
exposed film. The resultant radiograph would then have to
be interpreted in terms of quality parameters of the radiograph
and the subject of the radiograph evaluated in terms of
predetermined acceptance levels.
Advantages of Radiographic Testing?
1. Can be used with most solid materials.
2. Provides a permanent visual image.
3. Ability to detect internal flaws.
4. Discloses fabrication errors.
5. Reveals structural discontinuities.
Limitations of Radiographic Testing?
1. Impracticable to use on specimens of complex geometry.
2. Both sides of the specimen must be accessible.
3. Detection of laminar type discontinues & planar defects
may often be missed, unless they are favourably oriented.
4. Safety considerations imposed by X and g rays must be
considered.
5. Relatively large capital costs and space requirement
6. Field inspection usually restricted to 75 mm of steel
equivalent thickness.
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
to be qualified & certified 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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