What is Ultrasonic Thickness Gauging (UTG/UTT/UTM)? Advantage and Limitation Of UTG.

What is Ultrasonic Thickness Gauging (UTG)?

Ultrasonic Thickness Gauging (UTG) is a non-destructive testing (NDT) method used to measure the thickness of a material from one side only, using ultrasonic sound waves.

It is widely used in industries to check for corrosion, erosion, wear, and material thinning, especially when access to both sides of the component is not possible.

Principle of Operation:

• UTG works on the pulse-echo principle of ultrasonics:
• A transducer probe sends short ultrasonic pulses into the material.
• The sound wave travels through the material until it hits the back wall surface.
• The wave is reflected back (echo) to the transducer.
• The instrument measures the time of flight (TOF) between sending and receiving the echo.
• Knowing the velocity of sound in the material, the thickness is calculated: Thickness = Velocity of sound in material× Time of flight / 2        (The division by 2 is because the sound travels down and back.)

Types of UTG:

• Contact Method → probe directly contacts the surface.
• Immersion Method → part is submerged in liquid, sound travels through water.
• High-temperature UTG → special probes & couplants for hot surfaces.
• Corrosion Gauging → detects wall thinning in pipelines, tanks, boilers.

Key components of a UTG system:

Transducer: The probe that sends and receives the ultrasonic waves. Different types are used for specific applications:

Single-element transducers: Use one crystal for both transmitting and receiving, offering high precision on smooth surfaces.

Dual-element transducers: Have separate transmitting and receiving crystals, making them ideal for measuring rough, corroded surfaces.

Gauge: The electronic unit that generates the electrical impulses, receives and processes the signals from the transducer, and calculates and displays the thickness measurement.

Couplant: A gel, paste, or liquid applied to the surface to ensure proper acoustic contact and transmission of sound waves.

Advantages Of UTG:

• One-sided access is enough.
• High accuracy (±0.01 mm possible).
• Quick & portable measurements.
• Can measure thin or thick sections (0.5 mm to 500 mm, depending on probe).
• Safer than radiography (no radiation).

Limitations Of UTG:

• Requires smooth, clean surface (rust/paint may need removal).
• Sound velocity varies with material type & temperature, so calibration is important.
• Not ideal for very rough or uneven surfaces.