Manoharan Venugopal

Systematic Approach for Validation of X-Ray Automatic Defect Recognition Systems

With the advent of digital radiography, there has been a gradual shift from operators viewing images to find defects to totally automated defect recognition (ADR) systems. This has resulted in reduced operator subjectivity, reduced operator fatigue, and increased productivity. These automated defect recognition solutions are based on reference or non‐reference based approaches or a combination of both. There exists some amount of uncertainty or reluctance to accept automated systems in view of no systematic quantified metrics available on performance of these ADR systems in comparison to human operators. This paper describes the metrics that one could follow to quantify the performance of ADR systems such as detectability for different defect types and sizes, accuracy, false call rate, robustness to various noise levels etc., As it might be difficult to have images with defects of various sizes, shapes, contrast and noise levels, a methodology to generate images with simulated defects with variability’s i...

Beam Hardening Corrections in Quantitative Computed Tomography

Volumetric computed tomography (VCT) is the emerging 3D NDE inspection technique that gives highest throughput and better image quality. Industrial components in general demands higher x‐ray energy for inspection for which polychromatic x‐ray sources are used in common. Polychromatic nature of the x‐rays gives rise to non‐linear effects in the VCT projection data measurements called to be the beam hardening (BH) effects. BH produces prominent artifacts in the reconstructed images thereby deteriorating the image quality. Quantitative analysis such as density quantification, dimensional analysis etc., becomes difficult with the presence of these artifacts. This paper describes the BH correction using preprocessing technique for the homogeneous materials. Selection of effective energy at which the monoenergetic linear attenuation coefficient of a particular material equals to that of the polyenergetic beam is critical for BH correction. Various methods to determine the effective energy and their consequence in the quantitative measurements have been investigated in the present study. In this paper, BH corrections for heterogeneous materials have also been explored.Volumetric computed tomography (VCT) is the emerging 3D NDE inspection technique that gives highest throughput and better image quality. Industrial components in general demands higher x‐ray energy for inspection for which polychromatic x‐ray sources are used in common. Polychromatic nature of the x‐rays gives rise to non‐linear effects in the VCT projection data measurements called to be the beam hardening (BH) effects. BH produces prominent artifacts in the reconstructed images thereby deteriorating the image quality. Quantitative analysis such as density quantification, dimensional analysis etc., becomes difficult with the presence of these artifacts. This paper describes the BH correction using preprocessing technique for the homogeneous materials. Selection of effective energy at which the monoenergetic linear attenuation coefficient of a particular material equals to that of the polyenergetic beam is critical for BH correction. Various methods to determine the effective energy and their consequence ...

Quantitative Performance Assessment of Computed Radiography for Corrosion Detection in Process Pipes

Evaluation of integrity of process pipes in service is an important preventive maintenance issue for power generation and petrochemical industries. Ultrasonic wall thickness is traditionally used to measure wall thickness loss due to corrosion. This technique has various limitations such as need for removal of insulation, point based measurements and unsuitability for high temperature applications. Many have attempted computed radiography to quantify corrosion in pipelines as an alternative technique. Computed Radiography can be carried out without removing insulation and also at higher temperatures. However, the minimum detectability limit of wall thickness loss is limited by various physics complications in radiographic imaging process i.e. scattering, modulation due to detector response, focal spot blurring, the effective thickness of insulation and fluid inside pipe. An attempt has been made to study the effect of insulation and fluid inside pipe on detectability of wall loss due to corrosion using ph...