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APPLICATIONS OF RADIOGRAPHY

Because of the penetration and absorption capabilities of X and gamma radiation, radiography is used to test a variety of products such as welds, castings, forgings, and fabrications.

Radiographic testing is one of the primary non-destructive test methods in use today.

Radiographic testing usually requires exposing film to X or gamma rays that have penetrated a specimen, processing the exposed film, and interpreting the resultant radiograph.

ADVANTAGES OF RADIOGRAPHY (RT)

• Provides a permanent visual image.
• Reveals the internal nature of material.
• Discloses fabrication errors.
• Reveals structural discontinuities

LIMITATIONS OF RT

• Impracticable to use on specimens of complex geometry.
• The specimen must lend itself to two-side accessibility.
• Laminar type discontinuities are often undetected by RT Safety considerations
• Imposed by x and gamma rays must be considered.
• It is a relatively expensive means of non-destructive testing.

Training and certification

➤ It is important that NDT technician be qualified in the Radiography Testing method before the technique is used and test results evaluated.

➤ The American society for non-destructive testing recommends using ASNT SNT-TC-1A, 2020 edition for training, certification and recertification.

➤SNT-TC-1A provides the employer with the necessary guidelines to properly qualify and certify the NDT technician in all methods.

➤ To comply with SNT-TC-1A; the employer must establish a written practice that describes in detail how the technician will be trained, examined, and certified.

➤ Students are advised to study Latest edition of SNT-TC-1A to determine the recommended number of hours of classroom instruction and the required number of the months of experience necessary in order to be certified as a Radiography Testing technician.

Levels of qualification

In the process of being initially trained, qualified and certified, an individual should be considered a trainee. A trainee should work with a certified individual. The trainee shall not independently conduct, interpret, evaluate, or report the results of any NDT test.

➤ The three basic levels of qualification are as follows:

• NDT LEVEL I: He/she should be qualified to properly perform specific calibrations, specific NDT, and specific evaluation for acceptance or rejection determinations and record the results under supervision of a certified NDT LEVEL II or level III individual.

• NDT LEVEL II: He/she should be qualified to set up and calibrate equipment; interpret and evaluate results with respect to applicable codes, standards and specifications. He/she should be thoroughly familiar with the scope and limitations of the methods qualified and should supervise on the job training and guidance of trainees and NDT LEVEL I personnel. The NDT LEVEL II should be able to organize and report the results of NDT tests unsupervised.

• NDT LEVEL III: He/she should be capable of developing, qualifying, and approving procedures, establishing and approving techniques, interpreting codes, standards, specification and procedures; and designating the particular NDT methods, techniques and procedures to be used. The NDT level III should have sufficient practical background in the applicable materials, fabrication and product technology to establish techniques and to assist in establishing acceptance criteria when none are otherwise available.

The SNT-TC-1A document recommends that NDT LEVEL I and NDT LEVEL II technicians shall be examined in the following areas:

1. General examination
2. Specific examination
3. Practical examination

The SNT-TC-1A document recommends that NDT LEVEL III personnel be examined in the following areas:

1. Basic examination
2. Method examination
3. Specific examination

ASNT holds Level III examination and certification services in the Basic & Method areas.

Because of the individual requirements of the many industries using NDT, the SPECIFIC EXAMINATION is still the RESPONSIBILITY OF THE EMPLOYER.

Table 6.3.1 A: Recommended Initial Training and Experience Levels