Metrological investigation and calibration of reference standard block for ultrasonic non-destructive testing

Ultrasonic Non-Destructive Testing (NDT) is a powerful tool used for testing, verification, and inspection of material, especially for quality control and assurance. The key applications are the identification of flaws, cracks, irregularities, defects, and estimation of material thickness. The standard documents available for ultrasonic NDT are used as a guideline for the specifications and certification of the calibration reference standard block (RSB). The method for metrological characterization of the testing blocks is not specifically addressed in standard documents and is left to the wisdom of metrologists working in the ultrasonic calibration laboratories to adopt the suitable one. The ultrasonic flaw detector (UFD) is used most widely in ultrasonic NDT. The International Institute of Welding (IIW) V1 RSB standard is used as a reference to ascertain the functionalities of UFDs. In this article, we have proposed a new methodology for calibration of RSB and evaluation of associated measurement uncertainty along with influencing parameters. The proposed method conforms to the international standard ISO 2400:2012 and Indian standard IS 4904:2006 for validation purposes. According to these standards, the clauses for RSB e.g., dimension and quality of material have been examined. The expanded measurement uncertainty in thickness, ultrasonic longitudinal velocity, ultrasonic attenuation, parallelism and perpendicularity is ±0.068 mm, ±6.70 m/s, ±0.22 dB, and ±0.066 mm, respectively. The measurement uncertainty of these parameters is well within as per clauses stipulated in the standard documents except the ultrasonic longitudinal velocity for the IS standards.