Ultrasonic Velocity Chart
In Ultrasonic Testing (NDT), your equipment is only as good as your calibration. If you punch in the wrong velocity, your depth readings will be wrong, your defect location will be off, and you might just reject a good weld—or worse, accept a bad one.
Whether you are setting up a straight beam probe for thickness gauging or calibrating a 70° angle beam for weld inspection, having accurate Longitudinal and Shear Wave velocities at your fingertips is non-negotiable.
We have built a fully interactive UT Velocity Reference Chart below. You can search for materials instantly or download the entire table as a PDF for your field-book.
Check out the handy Ultrasonic Velocity Chart given in this article for an idea of the average speed of longitudinal ultrasonic waves in various materials. Keep in mind, these are just rough estimates. The actual velocity could be vastly different due to various factors like composition, structure, porosity, temperature, and more.
This is especially so in materials like cast metals, fiberglass, plastics, and composites. To ensure the most accurate thickness readings, it’s always best to calibrate the sound velocity in the test material by using a sample of known thickness.
Understanding Sound Velocity in NDT
Ultrasonic testing works on a simple principle: Distance = Velocity × Time.
The flaw detector measures time, but it relies on you to tell it the Velocity.
1. Longitudinal Wave Velocity (V_L)
- Used For: Thickness Gauging (0° Probes) and Straight Beam inspection of plates/forgings.
- Physics: The particle motion is parallel to the direction of wave propagation.
- Standard Steel: ~5,920 m/s (0.2330 in/µs).
2. Shear Wave Velocity (V_S)
- Used For: Angle Beam Inspection (Weld Inspection) with wedges (45°, 60°, 70°).
- Physics: The particle motion is perpendicular to the direction of propagation.
- Standard Steel: ~3,240 m/s (0.1280 in/µs).
- Rule of Thumb: Shear velocity is typically roughly half the longitudinal velocity.
3. Acoustic Impedance (Z)
- Formula: Z = Density \times Velocity
- Why it matters: The difference in impedance between two materials determines how much sound is reflected and how much is transmitted. This is critical for immersion testing or composite inspection.
Interactive UT Velocity Chart
Use the search bar below to find your material. Note that velocities can vary based on heat treatment and alloy composition. Always perform a 2-point calibration on a reference block of the same material before critical inspections.
UT Velocity Reference
Longitudinal & Shear Wave Speeds| Material | Longitudinal (m/s) | Shear (m/s) | Impedance (MRayl) |
|---|---|---|---|
| Air | 330 | – | 0.0004 |
| Aluminum (Rolled) | 6,320 | 3,130 | 17.1 |
| Steel (Mild/Carbon) | 5,920 | 3,240 | 46.0 |
| Steel (Stainless 304) | 5,660 | 3,120 | 45.4 |
| Steel (4340) | 5,850 | 3,240 | 45.0 |
| Brass (Naval) | 4,430 | 2,120 | 36.6 |
| Copper | 4,660 | 2,260 | 41.6 |
| Glass (Pyrex) | 5,640 | 3,280 | 12.7 |
| Iron (Cast) | 4,600 | 2,200 | 35.0 |
| Lead | 2,160 | 700 | 24.0 |
| Magnesium | 5,770 | 3,050 | 10.0 |
| Nickel | 5,630 | 2,960 | 49.5 |
| Plexiglass (Acrylic) | 2,730 | 1,430 | 3.2 |
| Polystyrene | 2,350 | 1,120 | 2.5 |
| Titanium | 6,070 | 3,120 | 27.3 |
| Tungsten | 5,180 | 2,870 | 101.0 |
| Water (20°C) | 1,480 | – | 1.48 |
| Oil (Transformer) | 1,390 | – | 1.39 |
| Zinc | 4,170 | 2,410 | 29.6 |
Ultrasonic Testing Velocity
Ultrasonic testing is a widely used non-destructive evaluation (NDE) method for evaluating the properties of engineering materials.
The method relies on the measurement of ultrasonic waves to determine the properties of a material such as its thickness, density, and elastic modulus.
The speed at which these ultrasonic waves travel through a material is known as the ultrasonic velocity.
In this article, we will explore the ultrasonic velocity chart, including a comprehensive list of engineering materials that are tested using ultrasonic testing and the relevant topics that are covered.
Ultrasonic Velocity Chart for Materials
The below ultrasonic velocity chart lists the longitudinal ultrasonic wave velocity at which ultrasonic waves travel through different materials.
The velocity is typically given in units of meters per second (m/sec) or inches per microsecond (in./µsec).
The chart includes a wide range of materials, including metals, plastics, ceramics, liquids, and composites.
| Material | V (in./µsec) | V (m/sec) |
|---|---|---|
| Aluminum | 0.2490 | 6320 |
| Beryllium | 0.5080 | 12900 |
| Brass | 0.1740 | 4430 |
| Copper | 0.1830 | 4660 |
| Inconel | 0.2290 | 5820 |
| Iron, Cast (soft) | 0.1380 | 3500 |
| Iron, Cast (hard) | 0.2200 | 5600 |
| Iron oxide (magnetite) | 0.2320 | 5890 |
| Lead | 0.0850 | 2160 |
| Lucite | 0.1060 | 2680 |
| Molybdenum | 0.2460 | 6250 |
| Nickel, pure | 0.2220 | 5630 |
| Steel, 1020 | 0.2320 | 5890 |
| Steel, 4340 | 0.2300 | 5850 |
| Steel, 302 austenitic stainless | 0.2260 | 5740 |
| Tin | 0.1310 | 3320 |
| Titanium | 0.2400 | 6100 |
| Tungsten | 0.2040 | 5180 |
| Zinc | 0.1640 | 4170 |
| Zirconium | 0.1830 | 4650 |
| Acrylic (Perspex) | 0.1070 | 2730 |
| Composite, graphite/epoxy | 0.1200 | 3070 |
| Diamond | 0.7090 | 18000 |
| Fiberglass | 0.1080 | 2740 |
| Glycerin | 0.0760 | 1920 |
| Motor oil | 0.0690 | 1740 |
| Polyamide | 0.0870 | 2200 |
| Nylon | 0.1020 | 2600 |
| Polyethylene, high density (HDPE) | 0.0970 | 2460 |
| Polyethylene, low density (LDPE) | 0.0820 | 2080 |
| Polystyrene | 0.0920 | 2340 |
| Polyvinylchloride, (PVC) | 0.0940 | 2395 |
| Rubber, polybutadiene | 0.0630 | 1610 |
| Silicon | 0.3790 | 9620 |
| Silicone | 0.0580 | 1485 |
| Water (20 °C or 68 °F) | 0.0580 | 1480 |
Materials Tested by Ultrasonic Testing
- Metals: Ultrasonic testing is commonly used to test the properties of various metals such as aluminum, steel, titanium, and copper.
- Polymers: Ultrasonic testing is also used to evaluate the properties of polymers such as polyethylene, polypropylene, and PVC.
- Composites: Ultrasonic testing is used to evaluate the properties of composite materials, including fiber-reinforced composites and carbon fiber composites.
- Ceramics: Ultrasonic testing is used to evaluate the properties of ceramics, including aluminum oxide and zirconia.
- Glass: Ultrasonic testing is used to evaluate the properties of glass, including soda-lime glass and tempered glass.
Ultrasonic Velocity Formula
The formula for ultrasonic velocity is given by:
V = √(E/ρ)
where: V = ultrasonic velocity (m/s) E = Young’s modulus (Pa) ρ = density of the material (kg/m3)
Field Tips for Technicians
- The “Temperature” Trap: Sound velocity changes with temperature. If you calibrate your machine on a cool morning (15°C) and inspect a hot pipe ($80°C) at noon, your depth readings will drift. Re-calibrate often.
- Cast Iron Warning: Notice the velocity for Cast Iron is much lower than Carbon Steel? The graphite flakes in cast iron slow down and scatter the sound. You cannot inspect cast iron using standard steel settings.
- Shear Wave conversion: If you only know the Longitudinal velocity, you can estimate the Shear velocity by dividing by approximately 1.82 (for steel), but never rely on math alone—verify with a calibration block (IIW or DSC).
Frequently Asked Questions about Ultrasonic Velocity
What is Ultrasonic Velocity in NDT?
Ultrasonic velocity is the precise speed at which sound waves travel through a specific medium. It is determined by the material’s density and elastic properties (Young’s Modulus). In Ultrasonic Testing (UT), correct velocity calibration is critical because the flaw detector measures time, not distance. If the velocity input is wrong, the depth reading of a defect will be incorrect.
How is Ultrasonic Velocity calculated?
Velocity (V) is calculated using the formula V = D / T, where D is the known thickness of a calibration block and T is the time of flight measured by the instrument. In the field, technicians perform a “2-Point Calibration” using a step wedge (e.g., measuring 5mm and 25mm steps) to calculate the exact velocity for that specific material batch.
Does temperature affect Ultrasonic Velocity?
Yes, significantly. As the temperature of a metal increases, the ultrasonic velocity generally decreases. This is because heating the metal reduces its elastic modulus (stiffness). A general rule of thumb for carbon steel is that velocity drops by approximately 1% for every 55°C (100°F) rise in temperature. You must re-calibrate if inspecting hot piping.
How does grain size affect Ultrasonic Testing?
Large or coarse grain structures (common in Cast Iron or Austenitic Stainless Steel) cause attenuation (signal loss) and scattering (grass/noise on the screen). While this affects the ability of the sound to penetrate the part more than the velocity itself, it often requires utilizing lower frequencies (e.g., 2.25 MHz instead of 5 MHz) and specialized probes to get accurate readings.
What is the difference between Longitudinal and Shear Wave velocity?
Longitudinal Velocity (Compression wave) is roughly twice as fast as Shear Velocity. It is used for thickness gauging and straight-beam inspection. Shear Velocity (Transverse wave) is slower and is used for angle-beam weld inspection. For Carbon Steel, Longitudinal velocity is ~5,920 m/s, while Shear velocity is ~3,240 m/s.
Why is the velocity of Stainless Steel different from Carbon Steel?
Even though both are “steel,” their alloying elements change their density and elasticity. 304 Stainless Steel typically has a longitudinal velocity of ~5,660 m/s, whereas Carbon Steel is ~5,920 m/s. If you use a Carbon Steel setup to measure a Stainless Steel pipe, your thickness reading will be dangerously inaccurate (reading thinner than it actually is).
Can I use a standard velocity chart for all inspections?
No. Velocity charts are for reference only. The exact velocity can vary based on heat treatment, rolling direction, and alloy composition. For code-compliant inspections (ASME/API), you must always calibrate your equipment on a reference block made of the same material as the part being inspected.
Material Welding is run by highly experienced welding engineers, welding trainers & ASNT NDT Level III bloggers.
We strive to provide most accurate and practical knowledge in welding, metallurgy, NDT and Engineering domains.
