Identification of cracks in gas pipes using digital radiography, wavelet and curvelet transforms

In oil and gas pipes, crack is one of the important defects that can lead to the pipelines fractures under high pressure and tension. This usually involves inconvenient and catastrophic events. Therefore, the timely identification of these cracks can prevent horrible human casualties and financial losses. In this research, digital industrial radiography NDT method was used to identify the cracks in the pipes. In many cases, the generated radiographs do not show clearly the defects and radiography images suffer from low contrast because of the photonic scattering of gamma and X-rays. In this research, an image processing method in wavelet domain was implemented. To improve the contrast, the curvelet method is used to make the defect areas more specific. The results show that this method has some superiority to conventional wavelets due to having higher (more emphasized) wavelets than the ordinary wavelets. So it is more capable of defining defect areas, especially in curvature regions. Radiography experts' judgments have been used to evaluate the results. The results of evaluation show that experts confirm the improvement of the contrast and more specific of the defect areas.