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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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