A method for assessing the X-ray equipment aging factor to correct the film exposure time

Abstract

Good quality radiographic images are essential for accurate medical diagnosis and reliable defect detection in welds. As X-ray equipment ages, the radiographic spatial resolution decreases because the focal spot area (FSA) enlarges, increasing geometric unsharpness and degrading image quality. To compensate for this degradation, operators often increase the film exposure time based on personal experience. This paper introduces a method for the systematic assessment of a dimensionless aging correction factor for the standard exposure time. Key geometric, thermal, and physical parameters involved in the aging process are combined into a dimensionless thermo-radiographic coupling index derived using the Buckingham-Pi theorem. This index, which links the thermally-induced strain demand to radiographic degradation, is used to develop a logistic growth model describing the time-dependent evolution of the FSA. The model is used to estimate time-dependent aging factors, which are illustrated using nomograms and applied to aged industrial X-ray equipment. The corrected exposure improves crack detectability and visibility of thin wires in Image Quality Indicators (IQIs). The findings of this paper provide a more consistent and physics-based assessment of exposure time, enhancing the reliable operation of aged medical and industrial X-ray equipment.