What is beam path length in ultrasonic testing?

Beam path is the distance the ultrasonic wave travels from the probe to the reflector. For angle beam: beam path = thickness / cos(angle). For the full V-path (skip): beam path = 2 × thickness / cos(angle).

What is skip distance?

Skip distance is the surface distance between the probe entry point and where the beam reflects off the back wall. Full skip = 2 × thickness × tan(angle). Half skip = thickness × tan(angle). Used for weld inspection positioning.

What is near field length?

Near field (Fresnel zone) N = D²f/(4v) where D = probe diameter, f = frequency, v = velocity. Within the near field, the beam has uneven pressure distribution. Inspections should be done beyond N for reliable results.

How does probe angle affect inspection?

Common angles: 0° for thickness measurement, 45° for detecting vertical flaws in welds, 60° for general weld inspection (most common), 70° for thin materials and near-surface flaws. Angle refers to refracted shear wave angle in the test material.

What frequency to choose for ultrasonic testing?

Higher frequency = better resolution but less penetration. 1-2 MHz for castings and coarse grain. 2-5 MHz for general steel inspection. 5-10 MHz for thin materials and high resolution. 10-25 MHz for precision measurement.

Free Engineering Tool

Ultrasonic Testing Calculator

Calculate beam path, skip distance, near field length, and wavelength for ultrasonic NDT inspections. Material velocity reference included.

NDT CalculatorBeam PathNear Field

UT Calculation Results

Beam Path (full V-path)

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Skip Distance (full)

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Half Skip Distance

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Near Field Length N

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Wavelength λ

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Velocity Used

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Material / Probe

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Min. Detectable Flaw

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Beam Path & Skip Distance

Near Field Length

Wavelength

Material Velocity Reference

Material	V_L (m/s)	V_S (m/s)	ρ (kg/m³)

Practical Example

Example — 60° angle beam on 25mm carbon steel

V_shear = 3250 m/s, t = 25 mm, θ = 60°

Half skip = 25 × tan(60°) = 25 × 1.732 = 43.3 mm

Full skip = 2 × 43.3 = 86.6 mm

Beam path = 2 × 25 / cos(60°) = 50 / 0.5 = 100 mm

N = 20² × 4×10⁶ / (4 × 3250) = 1600000/13000 = 123 mm

λ = 3250 / (4×10⁶) × 1000 = 0.81 mm

Ultrasonic Testing Calculator — Beam Path & Near Field | Vibromera

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026