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Ultrasonic NDT

Metal Coils Thickness Inspection

Published on 20th April 2021

Metal Coils Thickness Inspection

Batches of coiled steel often need to be inspected for compliance with thickness specifications. Conventional measurements are limited to the cut edges at the head of the coil. Ultrasonic thickness measurements, on the other hand, are made from one side only - the exposed side - making it possible to monitor the thickness over the entire width of the coil. Since the thickness can vary as much as 0.002 to 0.004 in. (0.05 to 0.10 mm) from edges to center, steel processors find great advantages in using small ultrasonic gauges.

Equipment: Selection of instrumentation depends on the accuracy that is required. The best accuracy can be achieved with the Model 38DL PLUS or 45MG with Single Element software gages with a 20 MHz (M208) or 10 MHz (M202) delay line transducer. In general, the calibrated accuracy with these gages combined with an M116 contact transducer is ±0.001 in. (±0.01 mm). In the High Resolution mode with an M208 or M202 delay line transducer they are capable of a calibrated accuracy of ±0.0003 in. (±0.008 mm) or better if thickness measurements are taken with delay line transducers under optimum circumstances. Continuous on-line thickness gaging can also be applied to coiled steel, using immersion type transducers. Contact us for details.

Products used for this application

The handheld 45MG ultrasonic thickness gauge is packed with measurement features and software options. This unique instrument is compatible with the complete range of Olympus dual element and single element transducers, making this gauge an all-in-one solution for virtually every thickness gauge application.


The 38DL PLUS is an advanced ultrasonic thickness gauge. Uses dual element transducer for internal corrosion applications, and has features that include THRU-COAT technology and echo-to-echo. Uses single element transducers for very precise thickness measurements of thin, very thick, or multilayer materials.


The 27MG is a basic ultrasonic thickness gauge designed to make accurate measurements from one side on internally corroded or eroded metal pipes and parts. It is lightweight, durable, and ergonomically designed for easy, one-hand operation.


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Application Notes