Which ultrasonic testing method is generally best for detecting discontinuities oriented along the fusion zone in a welded plate?

Which ultrasonic testing method is generally best for detecting discontinuities oriented along the fusion zone in a welded plate?

• A. An angle beam method using shear waves
• B. A straight beam method
• C. A through-transmission method
• D. A contact method using longitudinal waves

Answer: (A)

Discontinuities that run along the fusion zone are planar features aligned with the weld plane, so you want a wave setup that makes energy interact with that plane at a favorable angle. An angle-beam arrangement that excites shear waves does just that. By introducing the beam obliquely into the weld, the shear wave meets the planar defect in a geometry that produces a strong back reflection, making the defect most detectable. Shear waves are particularly responsive to crack-like and planar flaws, so the signal from a defect oriented along the fusion line stands out clearly. In contrast, a straight beam interrogates defects best when they are normal to the surface, which isn’t the case for a fusion-line flaw, so reflections can be weak. Through-transmission relies on energy passing completely through the plate and is less capable of pinpointing planar weld defects along the fusion line. Longitudinal waves in contact methods can detect surface and near-surface flaws, but they aren’t as sensitive to weld-oriented planes as an oblique-angle shear-wave inspection.

Discontinuities that run along the fusion zone are planar features aligned with the weld plane, so you want a wave setup that makes energy interact with that plane at a favorable angle. An angle-beam arrangement that excites shear waves does just that. By introducing the beam obliquely into the weld, the shear wave meets the planar defect in a geometry that produces a strong back reflection, making the defect most detectable. Shear waves are particularly responsive to crack-like and planar flaws, so the signal from a defect oriented along the fusion line stands out clearly.

In contrast, a straight beam interrogates defects best when they are normal to the surface, which isn’t the case for a fusion-line flaw, so reflections can be weak. Through-transmission relies on energy passing completely through the plate and is less capable of pinpointing planar weld defects along the fusion line. Longitudinal waves in contact methods can detect surface and near-surface flaws, but they aren’t as sensitive to weld-oriented planes as an oblique-angle shear-wave inspection.