Image processing of radiographs of tube-to-tubesheet weld joints for enhanced detectability of defects

This paper discusses the application of digital image processing, particularly Fourier space filters over the spatial filters, for enhanced detectability of defect features in the tube-to-tubesheet weld samples. The Butterworth band-pass filter is found to give optimal maximum signal-to-noise ratio (SNR) compared to other spatial and Fourier filters such as Sobel, Prewitt, Laplacian, Robert operator, ramp filter and Butterworth high-pass. The minimum pore size measurable using this approach is about 60 microns. Quantification of width of about 35 microns, for lack of fusion, is possible after applying the Butterworth band-pass filter. A flowchart has also been designed for regular application of digital image processing on radiographs of tube-to-tubesheet weld joints. The studies show that Butterworth band-pass filtering is ideal for enhanced evaluation of radiographs of tube-to-tubesheet joints with reliability and sensitivity.