A Complete Solution for Weld Inspections – Phased Arrays and Diffraction Sizing

Welds have been inspected by radiography for years, but this technology has major drawbacks: low detection rates for critical planar defects (i.e. cracks and lack of fusion), subjective interpretation, no vertical sizing capability, significant safety hazards, licensing issues, plant closures, and generally slow inspection rates. For decades, the main alternative was manual ultrasonics, which is also slow, subjective and has limited hardcopy recording. New technology and techniques are now available for improved weld inspections, specifically phased array technology and diffraction techniques. New portable phased arrays can now perform a single linear scan of the weld, performing multiple scans at different angles simultaneously. In addition, phased arrays can perform unique scans, like S-scans (sectorial scans), record and display all data in “top, side, end” views or similar, and perform multi-mode scans. Some estimates show that linear scanning with phased arrays is five times quicker than manual scanning. Besides being requiring just a single operator, portable phased arrays are now economically competitive with other weld inspection techniques. The “new” techniques consist of forward (Time of Flight Diffraction, or TOFD) and backward diffraction for sizing defects. Both these techniques have been around for decades, but new technology has made them more practical. TOFD has the major advantage that it is essentially angle-independent. Back diffraction has the advantages that it is intuitive, and can size defects down to ~1 mm, which is generally better than TOFD. Phased arrays can perform both pulse echo and TOFD simultaneously during a single linear scan, so giving essentially a “complete” weld inspection.