Ultrasonic technique for measuring the thickness of cladding on the

Abstract

An ultrasonic inspection method for measuring the thickness of non-welded (non-metallurgically bonded) cladding on the inside surface of a vessel from an outside diameter surface of the vessel relies upon the occurrence of a phase change at an interface between the base metal and cladding layers to precisely determine its presence and location. By measuring the length of time for the ultrasonic pulse to propagate through the cladding material, suitable predetermined calibration standards for the cladding material in question can be used to convert the time of flight of the ultrasonic pulses through the cladding into a thickness of the cladding. The cladding thickness can be measured from an outside surface of the vessel whether or not it is empty and/or without stopping the process and/or draining it, and the method can even be employed at elevated temperatures through the use of known delay lines. Alternatively, if safe access to the interior portion of the vessel is available, an internal direct inspection can be performed to determine the thickness of the non-welded cladding using a modification of the technique in which a first multiple or second reflection signal from the base metal/cladding layer interface is used.