Ultrasonic Thickness Measurement in Belgium
Ultrasonic thickness measurement is an essential NDT technique for corrosion monitoring, residual thickness assessment and determination of the remaining service life of industrial equipment. Rapid, precise and non-invasive, it is indispensable to any preventive maintenance programme.
What is Ultrasonic Thickness Measurement?
Ultrasonic thickness measurement is a specific application of ultrasonic testing that consists of accurately determining the thickness of a material by measuring the propagation time of an ultrasonic wave between the entry surface and the opposite surface (back-wall echo) or between two successive back-wall echoes. An ultrasonic probe emits a short pulse that travels through the material; knowing the ultrasonic velocity in the material concerned, the instrument calculates the thickness from the measured transit time.
This technique is of critical importance in the field of industrial maintenance and corrosion monitoring. Pressure equipment, piping, storage tanks and structures exposed to corrosive environments experience a gradual reduction in wall thickness over time. Ultrasonic thickness measurement enables this material loss to be quantified non-destructively, without requiring a plant shutdown or insulation removal (thanks to special high-temperature probes). The results obtained are essential for calculating the corrosion rate, determining the minimum residual thickness and assessing the remaining service life of the equipment.
LCNDTEST carries out ultrasonic thickness measurement campaigns on all types of industrial installations in Belgium. We use the latest generation of digital thickness gauges, calibrated and verified, offering a measurement accuracy of approximately 0.01 mm. Our technicians produce detailed thickness mapping and reports that enable our clients to plan their maintenance and replacement operations effectively, in compliance with Belgian and European regulations governing the safety of pressure equipment.
Measurement Methodology
Ultrasonic thickness measurement is performed using a dedicated measuring instrument (thickness gauge) fitted with a probe suited to the type of measurement being conducted. For standard measurements on accessible surfaces at ambient temperature, a dual-element probe (SE probe — Separate Emitter) is used, offering excellent resolution on thin sections and good tolerance to slightly corroded surfaces. For measurements on in-service equipment at high temperatures (up to 500°C and beyond), special high-temperature probes with an appropriate couplant are employed.
Surface preparation is critical to measurement quality: the measurement area must be cleared of any flaking paint, loose rust or scale to ensure good acoustic coupling. The instrument is calibrated prior to each measurement campaign using certified reference step wedges of known thickness, and the ultrasonic velocity is adjusted according to the material being measured. Measurement points are distributed according to a predefined grid pattern covering the areas of interest, with a tighter grid in zones most likely to be subjected to stress or corrosion.
The results are recorded digitally and compiled in a measurement report comprising a thickness map (graphical representation of measured values on an equipment layout), the calculated corrosion rate (by comparing current measurements with previous measurements or the original nominal thickness), the minimum residual thickness measured and its comparison with the minimum required thickness from the strength calculation. These data are essential for performing fitness-for-service assessments in accordance with reference standards such as API 579 / ASME FFS-1.
Industrial Applications
- Corrosion monitoring on industrial piping, transport pipelines and distribution networks
- Residual thickness measurement on storage tanks (bottoms, shells, roofs), atmospheric tanks and pressure vessels
- Inspection of heat exchangers: thickness measurement of tubes, tube sheets and shells
- Thickness measurement on marine and offshore structures (ship hulls, platforms, port structures)
- Wall thickness verification on new equipment during fabrication acceptance (dimensional inspection)
- Thickness measurement campaigns within the framework of regulatory inspection programmes and periodic requalification
Advantages of Ultrasonic Thickness Measurement
- Rapid, precise (0.01 mm resolution) and completely non-destructive measurement with no alteration to the component
- Single-side access: measurement possible even when the opposite face is inaccessible
- Applicable to in-service equipment, including at high temperatures, without requiring a production shutdown
- Quantitative data directly usable for remaining life calculation and maintenance planning
- Thickness maps enabling visualisation of the overall degradation state of the equipment and identification of critical zones
Reference Standards
EN 14127 • ASTM E797 • EN ISO 16809 • ASTM E114 • API 510 • API 570 • API 653 • API 579-1/ASME FFS-1
Frequently asked questions
Ultrasonic thickness measurement is critical for monitoring the condition of pressure equipment, piping, storage tanks and structures exposed to corrosion or erosion. Over time, these components lose wall thickness, which can compromise their structural integrity and safety. Regular thickness measurements allow engineers to quantify material loss, calculate corrosion rates, determine the remaining service life of equipment and plan maintenance or replacement before a failure occurs.
Modern digital ultrasonic thickness gauges offer a measurement resolution of approximately 0.01 mm (10 micrometres), providing highly accurate and repeatable results. The accuracy depends on proper surface preparation, correct calibration using certified reference blocks and appropriate selection of the probe type for the material and application. LCNDTEST uses the latest generation of calibrated instruments, verified and traceable to international standards, ensuring reliable measurements across all applications.
Ultrasonic thickness measurement can be performed on virtually any material that conducts sound waves, including carbon steel, stainless steel, aluminium, copper, titanium, nickel alloys, cast iron, plastics and glass. Special probes and instrument settings are available for different materials, and measurements can even be performed on in-service equipment at elevated temperatures (up to 500 degrees Celsius and beyond) using dedicated high-temperature probes and couplants.