How can UT differentiate between lack of fusion and porosity?

How can UT differentiate between lack of fusion and porosity?

• A. Lack of fusion is always larger than porosity.
• B. Porosity cannot be detected by UT.
• C. Lack of fusion usually presents as planar or elongated reflections at the seam with strong spacing; porosity appears as multiple small reflections distributed within the material; use multiple angles and calibration.
• D. Porosity appears as single large reflections.

Answer: (C)

In ultrasonic testing, you identify defect types by how the ultrasound interacts with the flaw: the shape, orientation, and distribution of reflections tell you what you’re dealing with. A lack of fusion is essentially a planar discontinuity along the weld seam, so it behaves like a large, flat reflector. When you scan, you’ll see a strong, elongated echo aligned with the seam, often spaced at a regular interval along the weld because the flaw runs along that plane. Porosity, by contrast, consists of many tiny gas pockets scattered through the material. Each pore reflects a small amount of energy, so you get multiple small reflections spread throughout the weld volume rather than one big planar echo. The pattern is more chaotic in nature and not tied to a single planar feature. Using multiple angles helps confirm the difference. A planar lack-of-fusion defect will produce echoes that follow the seam orientation and change predictably with angle, while porosity echoes are more randomly distributed in depth and position and may behave differently as angles change. Calibration with known standards also helps size and distinguish the echoes correctly. So, the description that lack of fusion appears as planar or elongated reflections at the seam with strong spacing, and porosity appears as multiple small reflections distributed within the material, with the use of multiple angles and calibration, is the best way to differentiate between the two.

In ultrasonic testing, you identify defect types by how the ultrasound interacts with the flaw: the shape, orientation, and distribution of reflections tell you what you’re dealing with. A lack of fusion is essentially a planar discontinuity along the weld seam, so it behaves like a large, flat reflector. When you scan, you’ll see a strong, elongated echo aligned with the seam, often spaced at a regular interval along the weld because the flaw runs along that plane.

Porosity, by contrast, consists of many tiny gas pockets scattered through the material. Each pore reflects a small amount of energy, so you get multiple small reflections spread throughout the weld volume rather than one big planar echo. The pattern is more chaotic in nature and not tied to a single planar feature.

Using multiple angles helps confirm the difference. A planar lack-of-fusion defect will produce echoes that follow the seam orientation and change predictably with angle, while porosity echoes are more randomly distributed in depth and position and may behave differently as angles change. Calibration with known standards also helps size and distinguish the echoes correctly.

So, the description that lack of fusion appears as planar or elongated reflections at the seam with strong spacing, and porosity appears as multiple small reflections distributed within the material, with the use of multiple angles and calibration, is the best way to differentiate between the two.