How is material velocity used in UT thickness measurements?

How is material velocity used in UT thickness measurements?

• A. Thickness = (velocity × time) / 2.
• B. Time = thickness / velocity.
• C. Velocity × time gives thickness.
• D. Time is divided by velocity to determine thickness.

Answer: (A)

In UT thickness measurements, you convert the measured travel time of an ultrasonic pulse into a physical thickness using the material’s sound velocity. The pulse travels from the probe to the far surface and back, so the recorded time is a two-way travel time. The distance the sound covers in that round trip is velocity × two-way time. Since the actual thickness is only the forward path (half of the round-trip distance), the thickness is given by thickness = (velocity × two-way travel time) / 2. This relies on having an accurate velocity value for the material, which can vary with temperature and material composition, so velocity must be known or calibrated for the condition in which you’re measuring. Using the wrong velocity will scale the thickness reading incorrectly. If you used a one-way time or omitted the factor of two, you’d miscalculate the thickness.

In UT thickness measurements, you convert the measured travel time of an ultrasonic pulse into a physical thickness using the material’s sound velocity. The pulse travels from the probe to the far surface and back, so the recorded time is a two-way travel time. The distance the sound covers in that round trip is velocity × two-way time. Since the actual thickness is only the forward path (half of the round-trip distance), the thickness is given by thickness = (velocity × two-way travel time) / 2.

This relies on having an accurate velocity value for the material, which can vary with temperature and material composition, so velocity must be known or calibrated for the condition in which you’re measuring. Using the wrong velocity will scale the thickness reading incorrectly. If you used a one-way time or omitted the factor of two, you’d miscalculate the thickness.