Uncertainty in Flaw Sizing by Radiography Method - A Primer Plus

Radiography is the most widely used volumetric examination technique for non- destructive evaluation of components, as it offers the advantage of direct viewing of the flaw image, judging the type of flaw and provides a permanent record. Flaw characterization methods, described by size, shape & location, require classification of the type or nature of flaw, position of flaw and flaw severity. Accurate sizing of the flaw to assess its severity is important. ISO Guide 25 “General Requirements for the Competence of Calibration and Testing Laboratories” (1990), requires one to specify the uncertainty of each measurement. In radiography there are several factors which contribute to uncertainty for quantitative measurement. This paper describes a study undertaken to calculate the uncertainty in flaw sizing and to estimate the real size of discontinuities observed in radiography.

Introduction

Radiography is widely used in industries for determining the quality of engineering components by detecting and sizing internal discontinuities . In any flaw detection technique, the probability of detection (POD) is less than 1 or 100%. Desired POD in radiography is considered between 0.8 & 0.9. The evaluation of radiographs is done in two steps:

1. Detecting the flaw
2. Dimensioning of flaw