Radiography (discussed in Section 14.5.2) is a nondestructive material testing method using X-ray or gamma radiation to image internal parts, structural defects, or internal structures of nontransparent materials, parts, or equipment. The main application is testing defects of welding seams by means of a radiography record (radiogram).

To make a radiogram, ionizing radiation leaving the source through a collimator penetrates the workpiece placed in front of the beam and replicates the internal structure of the material on a film placed on the opposite side (Figure 11.26).

A container with a source-controlling device is called a “defectoscope,” which is a structure on wheels. Its control unit is suitable for transporting the shielding container within the pipe to the spot of the welding seam, and it has a pneumatic device to pull the source out of the container for the length of the exposition. Prior to the exposition, the welding seam is covered outside the pipe with high-resolution photo film (Figure 11.27). To test steel structures for wall thickness between 15 and 65 mm, Ir-192 is used; between 20 and 90 mm, Cs-137 is used; and between 40 and 150 mm, Co-60 is used.

By means of radiograms, gas intrusions, slag intrusions, metallic intrusions, binding defects, welding defects, cracks, and surface deficiencies can be visualized.

Figure 11.28 A visualized catalyzer bed tested with a gamma-transmission technique.

A modern variant of industrial radiography does not search for material defects; rather, its objective is to visualize volumes, arrangements, and phases of materials to monitor the operation of equipment.

Radiation absorption executed with parallel movement of the detector and a gamma radiation source requires simpler techniques (Figure 11.28). In more com­plicated cases, a high number of detectors is installed, surrounding the entire equipment.

The measuring technique based on transmitting the entire volume of equipment was used, e. g., for testing the cross-sectional density distribution of distillation

Figure 11.29 Natural gamma borehole logging.

columns where, in addition to the substance distribution on trays, the disposition of the steam and liquid phase and their relative volume rate were determined. In another case, a transmission study of a catalyzer bed was performed (Figure 11.28).