Performance and verification of ultrasonic thickness measuring equipment

If you read the UT thickness measuring device manual, you may noticed that it is mentioned that the equipment conforms to the requirements of BS EN 15317. This article is a briefing for that requirements for Characterization and verification of ultrasonic thickness measuring equipment.

The performance & verification tests are categorized into 3 groups:

Group 1 Tests: performed by the manufacturer on a representative sample of the ultrasonic thickness measuring equipment produced.

Group 2 Tests: performed on all ultrasonic thickness measuring equipment by the manufacturer prior to the supply of the equipment, test performed at annual intervals to verify the performance of the equipment by manufacturer/owner/laboratory or tests performed following any equipment repairs.

Group 3 Tests: Performed by the operator at site prior to and at the completion of any series of measurements.

The photo below addresses the tests for each group.

If you are reviewing the calibration certificate for a device, you will focus on group 2 test.

There are requirements for the calibration blocks used in such tests, generally the material is from steel grade S355JO specified in EN 10025-2, be rough-machined before heat treatment which shall consist of austenitizing at 920 "C for 30 min, rapid cooling (quenching) in water, tempering by heating to 650 'C for 3 h; and then cooling in still air. The velocity far longitudinal waves in the calibration block material shall be (5920+/-30) m/s and the surfaces used for measurement shall be machined to an Ra value not greater than 0.8 μm. It is permissible to chromium plate or electroless nickel plate the surfaces of the block to a maximum of 0.5 % of the block thickness.

There are 2 types of blocks are being used generally, accuracy blocks are 5 cylinders with max. & min. lengths equal to the max. & min. ranges of thickness for the device, resolution blocks are step blocks, step height is less than the resolution of the device.

When performing calibration mechanisms to meet group 3 requirments, Select the recommended probe for the material and range of thicknesses to be measured, complete the probe zeroing operation according to the manufacturer's instructions, use a calibration block made of the same material as that which is to be measured and of a thickness in the range expected to be measured and adjust the system's material vebcity setting. The obtained readings shall be within the manufacturer stated accuracy for the device.

And finally, calibration is very important because it helps ensure reliabilty of instruments, accurate measurements, and accurate measurements are foundational to the quality.