Detection, 3-D positioning, and sizing of small pore defects using digital radiography and tracking

Erik Lindgren

doi:10.1186/1687-6180-2014-9

Abstract

This article presents an algorithm that handles the detection, positioning, and sizing of submillimeter-sized pores in welds using radiographic inspection and tracking. The possibility to detect, position, and size pores which have a low contrast-to-noise ratio increases the value of the nondestructive evaluation of welds by facilitating fatigue life predictions with lower uncertainty. In this article, a multiple hypothesis tracker with an extended Kalman filter is used to track an unknown number of pore indications in a sequence of radiographs as an object is rotated. Each pore is not required to be detected in all radiographs. In addition, in the tracking step, three-dimensional (3-D) positions of pore defects are calculated. To optimize, set up, and pre-evaluate the algorithm, the article explores a design of experimental approach in combination with synthetic radiographs of titanium laser welds containing pore defects. The pre-evaluation on synthetic radiographs at industrially reasonable contrast-to-noise ratios indicate less than 1% false detection rates at high detection rates and less than 0.1 mm of positioning errors for more than 90% of the pores. A comparison between experimental results of the presented algorithm and a computerized tomography reference measurement shows qualitatively good agreement in the 3-D positions of approximately 0.1-mm diameter pores in 5-mm-thick Ti-6242.

Highlights

Radiographic inspection is frequently used within the manufacturing industry to detect and characterize defects in a wide variety of structures
The size together with its distance to other defects and to the surface are known to affect the fatigue life of the structure [1]. This results in three issues: firstly, the size is of interest to measure in itself; secondly, the size is of interest since assuming no interaction between the defects, the smallest defect that can be detected with high probability, will be a parameter limiting the predicted fatigue life; and thirdly, the distance which is of interest is in three-dimensional (3-D)
7 Conclusions In this article, an algorithm has been derived to handle the detection, positioning, and sizing of submillimetersized pore defects in thin laser-welded titanium inspected with radiography

Summary

Introduction

Radiographic inspection is frequently used within the manufacturing industry to detect and characterize defects in a wide variety of structures. The size together with its distance to other defects and to the surface are known to affect the fatigue life of the structure [1]. This results in three issues: firstly, the size is of interest to measure in itself; secondly, the size is of interest since assuming no interaction between the defects, the smallest defect that can be detected with high probability, will be a parameter limiting the predicted fatigue life; and thirdly, the distance which is of interest is in three-dimensional (3-D). The second approach is based on not reconstructing the whole volume but rather by focusing on reconstructing the 3-D position of each defect, referred to as point reconstruction methods [5]. The 3-D position of the defect is calculated using the defect projection coordinates in the image plane for a few rotations and/or translations

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Conclusion