DETECTION OF AXIAL CRACKS IN TUBE AND PIPE USING TORSIONAL GUIDED WAVES

Guided‐waves are now widely used for long‐range inspection of piping and tubing for detection of corrosion metal loss areas and circumferential cracks. The reflection coefficient of guided‐waves from a defect is proportional to the circumferential cross‐sectional area of the defect. Since axial cracks have negligibly small circumferential cross‐sectional area, they are usually undetectable. However, when the depth of axial crack reaches about 70‐percent of wall thickness, the interaction mechanism between the torsional wave and the axial crack changes and the crack begins to produce detectable signals accompanied with characteristic tailing signals. Experimental data from various sized pipes including a seam‐welded pipe with lack of fusion are presented and potential interaction mechanisms are discussed.