Wall Thickness Gauges - Knowledge Base
Understanding Wall Thickness Measurement
Wall thickness measurement is an essential process in industries such as metal fabrication, shipbuilding, plastics production and packaging inspection. It allows technicians to verify material integrity and detect wear or corrosion without cutting or damaging the part.
Two main non-destructive technologies are used for this purpose: ultrasonic and magnetic.
Each operates on a different principle and is suitable for specific materials and measurement conditions.
1. Principles of Wall Thickness Measurement
Wall thickness gauges determine the distance between two opposite surfaces, typically the inner and outer walls of a material. Accurate readings depend on the physical properties of the material, surface condition, and calibration quality.
The two primary methods are:
- Ultrasonic measurement, based on sound wave reflection.
- Magnetic measurement, based on magnetic field detection through non-metallic materials.
2. Ultrasonic Thickness Gauges – Technology and Use Cases
Ultrasonic gauges emit high-frequency sound waves that travel through the material and reflect from the rear surface. The instrument calculates thickness based on the echo time.
Key Advantages:
- Measurement from one side only
- Works on metals, plastics, composites and glass
- Available in single- and dual-element probe versions
- Echo-Echo modes for readings through coatings and paint
- Reliable and repeatable readings under most conditions
Typical Applications:
Corrosion monitoring in steel structures, quality control in plastic components, inspection of ship hulls, pipelines, tanks, and pressure vessels.
3. Magnetic Thickness Gauges – MiniTest FH Principle
Magnetic gauges are designed for non-magnetic materials such as glass, plastic and aluminium. They use a magnetic probe on the outside and a small steel ball placed inside the test object. The gauge measures the magnetic field strength to determine the wall thickness.
Key Advantages:
- Ideal for thin, transparent or curved parts
- No couplant or disassembly required
- Suitable for limited internal access or narrow diameters
- Compact, portable and easy to use
Typical Applications:
Measurement of glass and plastic bottles, medical containers, films, tubes and other non-metallic components.
| Feature | Ultrasonic Measurement | Magnetic Measurement |
|---|---|---|
| Materials: | Metals, plastics, composites | Non-magnetic (glass, plastic, aluminium) |
| Access required: | One side only | Inside and outside |
| Couplant: | Required | Not required |
| Accuracy: | High | High for thin walls |
| Best for: | Corrosion, metals, composites | Transparent or non-metallic materials |
For more information on each Method, check out our knowledge base on Ultrasonic Measurement and Magnetic Measurement. |
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5. Selecting the Right Type of Gauge
Choosing the correct technology depends mainly on:
- Material type (metallic, plastic, glass, composite)
- Access (one side vs both sides)
- Wall thickness range
- Surface condition
Ultrasonic gauges are ideal for metallic or dense materials where only one side is accessible.
Magnetic gauges are preferred for non-metallic or transparent materials with limited internal access.
For assistance, our technical team can help you identify the correct model, probe and accessories for your specific process.
6. Typical Industrial Applications
- Metal and steel production – corrosion detection, material verification
- Plastic and composite manufacturing – uniform wall control
- Packaging industry – film and bottle wall analysis
- Shipbuilding and aerospace – structural inspection
- R&D and quality control labs – prototype testing, material analysis
7. Recommended Accessories and Calibration Tools
- Certified and standard calibration blocks
- Coupling fluids and gels
- Replacement transducers and cables
- Magnetic balls and sensors for MiniTest FH
- Test stands for repeatable measurement setups
Need further guidance?
Our application specialists can assist you in selecting the correct gauge, probe and configuration for your specific materials and inspection conditions.
8. FAQs – Wall Thickness Measurement
If it’s non-metallic, transparent or internally inaccessible, choose magnetic.