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.

The research presented in this paper investigated the effect of low temperatures on acoustic properties in coupling fluid and rail steel. The study focused on the effect of low temperature conditions on ultrasonic attenuation and velocity. The work introduces practical considerations for improving the quality of ultrasonic testing (UT) performed in cold weather. The study investigated common coupling fluids used in rail detector cars equipped with liquid-filled tires that house ultrasonic transducers. Velocity measurements of longitudinal waves propagating through the fluid and reflecting from a steel disc target were conducted. Steel properties were studied by fabricating two specimens from the head and web of two different 136RE rails sections. Velocity of longitudinal waves and mode-converted shear waves as well as attenuation measurements were conducted in rail specimens with side drilled holes (SDHs) at different depths. The tests were performed in an ultrasonic immersion tank integrated with a heat exchanger and chiller bath to obtain the targeted test temperatures ranging from -50° C to +20° C. The coupling fluid test results showed a linear increase in the ultrasonic velocity as the temperature decreased with a rate that ranged from -2.70 m/sec/° C to -1.83 m/sec/° C for the tested fluids. The test results also showed increased velocity in rail steel with decreasing temperatures with an average rate of -0.65 m/sec/° C for longitudinal waves and an average rate of -0.33 m/sec/° C for shear waves. These results indicate that temperature-dependent velocities must be used to obtain the desired refraction angle and adjustments to amplitude-based acceptance criteria may be needed to ensure uniform acceptance/rejection capabilities across all potential inspection temperatures.

Ultrasonic testing is utilized to ensure weld quality during the fabrication of steel bridges by identifying discontinuities that are classified as either acceptable or rejectable. The classification of a discontinuity can be affected by differences in the acoustic properties of the material under test and the reference standard used for calibration. Differences in wave velocity affect the refracted angle and amplitude of refracted shear waves. As a result, indications can be missed or incorrectly classified, or incorrectly located in the material. The objective of this research study was to characterize the acoustic wave velocities in a sample of contemporary steels to better understand the range over which velocities may vary for common steels. To address this objective, a series of velocity measurements have been conducted for shear waves propagating through different directions in steel plates of different strengths and reported manufacturing processes. The study also examines the loss of signal amplitude that results from changes in the refracted angle of shear waves used for the inspection of welds. Beam splitting that may occur in anisotropic materials and the potential impact on signal amplitudes is also presented. It was shown in the research that relatively small differences in velocity between the material under test and the reference standard cause a loss of sensitivity of the test. Data presented in the paper documents wave velocity and anisotropic ratios for a population of contemporary bridge steels used for the fabrication of steel bridges and an assessment of how velocity differences affect the amplitude of reflected shear waves.