When thickness survey of boiler tubes performed, some observations were showing thickness of the boiler tube more than the original thickness. Possible reason could be -
Oxide layer
The presence of an oxide layer on the outside of the tube can interfere with the measurement. The oxide layer can be rough, which prevents proper sound coupling, and the thickness of the oxide is added to the steel thickness.
Surface roughness
The surface of the test piece should be smooth for accurate measurements. If the surface is rough, the minimum thickness that can be measured will increase.
Remarks : In such a case operator can show the performance of Digital Thickness Gauge on standard thicknesses to satisfy customers.
