On Parameters Affecting the Sensitivity of Ultrasonic Testing of Tubes: Experimental and Simulation

The response (amplitude) of the reference notch during ultrasonic testing of tubes is dependent on several parameters like (1) size, shape and location of notch in the material (2) operating parameters like pitch, incidence angle, focusing, beam profile etc (3) Electronic parameters like PRF, pulse width etc. A thorough analysis of several parameters is made in this paper which affects the calibration sensitivity and its repeatability. Calibration during ultrasonic testing of tubes is carried out by using reference notches made on the tubes. The size and shape of the reference notches are defined in the specification of the tube. Different specifications like ASTM, ASME, AMS, BS etc recommend the type of notch to be used for calibration. These are varying from one standard to another and there is no comparison available for the achieved sensitivity during calibration. This paper deals with a comparison of the recommended size and shape of the notches in different codes and specifications. The sensitivity of test is dependent on the calibration notch size and shape. In the present work a comparison is made on the sensitivity (in terms of gain level) for different size and shape of notches used during calibration of a tube. Usually, these notches are made on the ID and OD surface of the tubes which are generally equal in size. During calibration equalization of the amplitude of indication from the ID and OD is recommended. However no sound basis is available for the reason for unequal amplitude indication from ID and OD notch. In the present work, response from the notches at ID and OD is experimentally determined and compared with modeling of the response from the ID and OD notches. The repeatability of the calibration is demonstrated by carrying out a series of repeated measurements of the gain of the response from the notch. Different specifications recommend different tests for demonstrating the repeatability of the calibration. A comparison is made here for the repeatability requirements in different specifications. An analysis of the operating and electronic parameters responsible for variation in gain during a repeatability test is made.