Influence of chemical composition and microstructural parameters on speed of sound of various materials used for high-pressure applications

A device for determination of wall thickness and centricity of high strength tubes during deep-hole drilling was designed. The system is equipped with an immersion transducer for wall thickness evaluation and an analogue inductive proximity sensor for detection of centricity. To achieve reliable results, it is crucial to apply correct values for the speed of sound in the investigated materials. For high pressure vessels and tubes it is common to use wrought high-strength, quenched and tempered steels (e.g. 1.6580) as well as martensitic corrosion-resistant steels (e.g. 1.4006). To reduce measurement uncertainty of wall thickness evaluation, the influences of chemical composition, microstructure, orientation and heat treatment condition on speed of sound of various materials were determined. Significant differences in sound velocities were obtained between normalized, quenched and quenched + tempered conditions. Furthermore, speed of sound was slightly higher in radial compared to axial direction in case of material 1.6580. In addition, sound velocities in one austenitic corrosion-resistant alloy and one super duplex stainless steel after different heat treatments were obtained. Results were utilized for calibration of the wall thickness measurement device in order to improve the accuracy of ultrasonic testing. As an outcome of this work, in-situ wall thickness evaluation during deep-hole drilling will be established as a standard characterisation method at BHDT GmbH, Austria.