What Does Clad Layer Thickness Checking Mean?
Clad layer thickness checking is performed on corrosion resistant alloys (CRA) that have been put through a cladding or weld overlay process on the equipment. A clad layer thickness check is performed using equipment known as a clad thickness measurement system, which has magnetic sensors. The primary application is non-destructive evaluation of industrial reactors and pressure vessels that are cladded with CRA.
Corrosionpedia Explains Clad Layer Thickness Checking
Ultrasonic testing (UT) can determine the total flaw depth on a surface, but the depth into the base metal cannot be measured precisely unless the cladding thickness is known. A magnetic clad sensor is used for this purpose. In another similar application, the sensor is used to measure the thickness of Inconel attachment weld areas on the inner walls of boiling water reactor (BWR) pressure vessels.
The clad thickness measurement system is based on a magnetic technique that responds to the distance between the probe that is placed on the clad surface or attachment weld surface and the ferromagnetic steel base metal. This distance is equal to the clad or weld thickness. Because welded stainless steel clad contains some ferrite, it is also slightly ferromagnetic, and therefore its presence must be accounted for by calibrating on a block with welded stainless clad of different thicknesses. Inconel welds are non-ferromagnetic; therefore, a calibration can be performed using nonmagnetic material.