SECTION IX RT PROCESS CONTROL

T.O. 33B-1-1 SECTION IX RT PROCESS CONTROL 1.9 PROCESS CONTROL FOR RADIOGRAPHY. 1.9.1 Scope and Purpose. Process control for radiography or other methods of inspection means that all the variables involving, materials, equipment, personnel, and documentation are well-defined and that the features that are significant in terms of process reliability be identified so that controls can be put in place. 1.9.1.1 For radiographic inspection, control features include variations in the radiation source, voltage, current, heat removal, and geometry factors such as focal spot size, shape and location, beam collimation and direction, and source-to-object and source-to-detector distances. Variations can also occur in the object and detector area in terms of the placement of the object (and penetrameters or image quality indicators) and the detector. In the case of film radiography, the storage and handling of the film, screens, and cassettes are an important variables to be brought under control. For the most part control of these variables is dependent on the radiographic inspector and the care the inspector uses in setting up all these features. Good record keeping is important in maintaining reliability. 1.9.1.2 A major variable in the radiographic process is the processing of the film. Concentration of processing chemicals, contaminants, and temperature are important variables. A method of monitoring changes in film processing involves the processing of many control-exposed films periodically to detect changes in film density and/or contrast. This can be implemented by radiographing a step wedge at time zero; this SHALL be at the beginning of each month. The film exposed to all the various gray levels from the step wedge can be cut into strips, each strip to be processed at various times after the identical exposures. For example, strip No. 1 would be processed immediately, as the control film. Densities and contrast between selected steps can be measured with a densitometer. Periodically, once a week, another film strip shall be processed and the densities and contrasts compared to those of the control film. Major variations in the densities of the films should lead to further examination of the film processing procedure. Variations in excess of 0.3 density units from anticipated film density values would be considered a major variation (a factor of 2 in transmitted brightness). Small variations may be tolerated. The experience of several months should provide scatter data that the radiographer will recognize as acceptable. The last strip in the control exposure should be processed with the control film of the new batch to maintain continued control from month to month. In cases where films from one manufacturer are processed in another film manufacturer’s recommended solutions, the period between control tests should be shortened. 1.9.1.3 The radiographic inspector should implement the control strip to detect changes in the radiographic process. If the inspector sees to it that the equipment is properly maintained, takes care to use the equipment in a repeatable manner, maintains good records, and maintains the repeatability of film processing, then the radiographic inspection process will remain in good control. 1.9.2 Radiographic Process Control Requirements. This requirement centers around film processing however the whole x-ray process must be closely controlled to produce the expected results. X-ray is a cure all to the novice, but to the informed it is a very costly and sometime inaccurate NDI method. Every aspect of the x-ray process must be right for the quality and probability of detection to be what we want. X-ray procedures SHALL be followed precisely. Proper beam alignment, the correct film, source focal spot size, and correct exposure parameters are critical. This radiographic process has many factors that effect the quality of the final product. One you must continuously check is the manner in which the film is handled. 1.9.2.1 Process Control in the Darkroom. For efficiency and reducing the possibility of damaging radiographic film, two distinct areas should be established within the darkroom. One area being designated the ‘‘dry area’’ and the other the ‘‘wet area.’’ Change 2 1-71