Nondestructive Transmission Tomography of Pipeline Surface Defects

Based on results of theoretical analysis, a new method of transmission tomography of pipeline surface defects using ultrasound waves propagating along the pipeline walls is proposed. The waves are excited by a source and received by sensors that are located on ring-shaped lines and spaced along the tube surface. These waves propagating along the pipe surface represent either left or right handed rectilinear cylindrical waves like torsion waves. When a defect arises on the pipeline surface, the resulting waves are accompanied by changes in their shadow projections at the controlled pipe end. The problem of defect tomography is to determine locations and forms of defects using the backward projections. The physical feature of this method is that unlike traditional tomography, these projections arise on mutually intersecting left and right handed trajectories. The problem is solved by multiple joining of cylindrical pipe sections unfolded onto the plane in which all wave paths become rectilinear. A number of examples given in the paper confirm the possibility of restoration of locations and forms of various defects by the proposed method.