Radiographic Testing Method Basic Knowledge

The radiographic testing method is used for the detection of internal flaws in many different materials and configurations. An appropriate radiographic film is placed behind the test specimen Figure and is exposed by passing either X rays or gamma rays (Co-60 & Ir-192 radioisotopes) through it. The intensity of the X rays or gamma rays while passing through the product is modified according to the internal structure of the specimen and thus the exposed film, after processing, reveals the shadow picture, known as a radiograph, of the product. It is then interpreted to obtain data about the flaws present in the specimen. This method is used on wide variety of products such as forgings, castings and weldments.

Some of the advantages of radiographic testing include:
(1) It can be used to inspect large areas at one time.
(2) It is useful on wide variety of materials.
(3) It can be used for checking internal malstructure, misassembly or misalignment.
(4) It provides permanent record.
(5) No calibration needed on the job site.
(6) Devices for checking the quality of radiograph are available.
(7) Interpretation of radiographs can be done in comfortable conditions.

Some of the limitations of this method are:
(1) X rays and gamma rays are hazardous to human health.
(2) It cannot detect planar defects readily.
(3) Access to both sides of the specimen is required.
(4) Thickness range that can be inspected is limited.
(5) Certain areas in many items cannot be radiographed because of the geometric consideration.
(6) Sensitivity of inspection decreases with thickness of the test specimen.
(7) It is more costly.
(8) It cannot be easily automated.
(9) It requires considerable skill for the interpretation of the radiographs.
(10) Depth of discontinuity not indicated.

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