Portable computed tomographic system for in-situ inspection of industrial pipelines

Computed tomography (CT) provides a cross-sectional view of the interior of ail object. The invention of the CT scanner revolutionised the field of medical diagnostic imaging because it provided more detailed and useful information than any previous non-invasive imaging techniques. For the same reason, the method is being used increasingly in industry. A wide variety of applications have arisen over recent years for non-destructive testing (NDT). Among advantages of using CT techniques in industry are that they are rapid, reliable, and, for most applications, can be used in places where no other techniques are applicable such as in aggressive environments or where control measurements must be made through the walls of vessels. More importantly, these techniques allow the results to be obtained in real time, thus enabling the measurements to be used for on-line process investigations. Measurements are accomplished non-destructively and without changing any properties of the examined material. This paper presents the development of a portable computed tomographic scanner for on-line imaging of industrial piping systems. Its design is based upon a third generation computed tomography system but is arranged so that the ray-sum data is acquired in such a way to be essentially equivalent to a first generation sinogram. This leads to a reconstruction process that requires no explicit ray-sum interpolation, and importantly, produces more accurate reconstructed CT images than current third generation systems. The idea of this design arose from a comprehensive study of the similarities and differences between parallel beam (first generation) and fan beam (third generation) X-ray and gamma-ray CT systems. This paper provides background information oil the development of the portable computed tomographic scanner. The theoretical approach, the system hardware, the data acquisition system and the adopted algorithm for image reconstruction are discussed. The scanner has large potential to be used to determine the extent of corrosion under insulation (CUI), to detect blockages, to measure the thickness of deposit/materials built-up on the walls and to improve understanding of material flow in pipelines.