Radiography of thin-section welds, Part 4: Further modelling

Abstract

This paper describes the further refinement of a simple model of radiography, first published by Pollitt in 1962, which treats flaws as smooth, parallel-sided slots. It builds on the work on thin-section welds presented at NDT'02, and earlier work by TWI on thicker welds. The latest experimental data were collected from 13 realistic planar flaws in welds of thicknesses 10-50 mm. They were radiographed under various exposure conditions, giving 284 flaw/radiograph combinations (supplementing 333 flaw/radiograph combinations already available from earlier work on thicker welds). Each radiograph was evaluated 'blind' by two radiographers. The specimens were then sectioned to determine defect size, orientation and gape. A separate paper at this conference (Part 3) describes the practical aspects of the work. The experimental data show variations in detectability that are strongly correlated with theoretical predictions. The broader range of the available experimental data has enabled us to improve the accuracy of our previously published statistical models for the reliability of radiography. Different models are proposed in the cases of: □ large planar flaws (≥15 mm in through-wall extent) in thick-section welds. □ small planar flaws (<8 mm through-wall) in thin-section welds, and □ small flaws of complex morphology in thin-section welds.