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Abstract: The seamless tube-making process often causes wall-thickness variations generally in a helical pattern along the tube length. A laser-ultrasonic system installed immediately after the final operation in tube making provides process monitoring. Tube wall thickness and temperature measurements guide the mill adjustments to achieve the desired tolerances. Using the same ultrasonic signals, additional functionality provides the ability to measure the size of austenite grains. A signal processing approach based on a single echo analysis is used for determining wall thickness and austenitic grain size in relatively thick materials. Discussions review challenges specific to on-line conditions such as limited signal-to-noise ratio. A statistical comparison with metallographic results shows that the laser-ultrasonic grain sizes determined on-line have at least the same accuracy. [Copyright &y& Elsevier]