The Similarities Between Ultrasonic Thickness Gauges and Flaw Detectors

Ultrasonic thickness gauges and flaw detectors use the same basic concepts. They both use transducers that generate sound waves and both measure the time it takes for that sound to leave a transducer, travel through a material, bounce off a reflector, and return to the transducer.

A sound pulse generated by a transducer travels through a test piece and reflects back from the inside surface or far wall

And both use the basic equation of:

Distance = (Velocity x time) / 2

This equation divides by two since the one-way time measurement to the reflector is all that’s required.

The reflection and transmission of high-frequency sound waves—known as ultrasound—has long been an important tool for evaluating the integrity of welds, as well as testing structural metals, pipes and tanks, boiler tubes, railroad rails and axles, aerospace composites, and many other industrial applications.

Industrial ultrasonic testing equipment continues to be popular since it:

• Is cost effective, quick, and reliable
• Usually requires no test piece preparation other than wetting with couplant
• Has no specific safety hazards or regulatory licensing requirements associated with its use

Selecting an ultrasonic thickness gauge or flaw detector for an application largely depends on the main goal of the measurement. Before we get into the key differences between these instruments, let’s take a brief look at their use throughout the years.

Advantages of an Ultrasonic Thickness Gauge

Here are some advantages of an Olympus ultrasonic thickness gauge:

• More consistent and accurate time-of-flight (ToF) measurement. Straight beam inspection measures the ToF to a material’s back surface, which corresponds to the total thickness of that material.
• Compact size and lower cost.
• Easy to calibrate and operate.
• Specialized features or software for unique application needs, including boiler tube measurements, high temperature, and painted or coated applications.
• Measurement advantages include:
  • Auto zero compensation: enables a more precise zero offset measurement, which contributes to a more accurate ToF measurement.
  • V-path correction: compensates for the angular sound path of corrosion measurements using a dual element transducer, providing the highest degree of accuracy and repeatability over a large thickness range. Most flaw detectors do not compensate for this angular sound path.
  • Auto probe recognition: the D79X series of dual element transducers includes an auto recognition pin, enabling the gauge to recognize the transducer; this eases user operation by recalling the optimized setup and receiver gain, and also determines the transducer’s pre-recalled V-path correction.
  • Detection algorithms and digital signal processing (DSP): allows the calibrated accuracy to be maintained when gain or signal amplitude changes.

Advantages of an Ultrasonic Flaw Detector

Here are some advantages of an Olympus ultrasonic flaw detector:

• Highly versatile:

  • Straight beam inspection measures to a defect or a void to locate the distance to the flaw from the material’s surface.

  • Angle beam inspection to check the integrity of welds.

  • Ideal for scanning applications (due to a faster update rate of 60 Hz compared to a 25–30 Hz update rate of a thickness gauge)

• Includes specialized software for sizing defects:

  • Distance amplitude correction (DAC)

  • Time varied gain (TVG)

  • Distance gain sizing (DGS)