Wall Thickness Measurements by Ultrasonic Probes in a Liquid Rocket Combustion Chamber

The regenerative cooling combustion chamber of a liquid rocket engine is exposed to a large temperature difference between the combustion gas and the liquid fuel. To estimate the inner wall damage, an evaluation of wall deformations is very important since chamber life is usually related to such deformations. In this study, the ultrasonic thickness measurement technique based on the pulse reflection method was chosen and conducted the measuring tests of ligament thicknesses and the analyses of ultrasonic wave propagations. Two types probe were manufactured which have a polystyrene and a local immersion delay. From the test and the analysis results with a polystyrene delay, it was shown that the b1 echo could not stably obtained in an A-scan graph and measurement accuracy was not sufficient in measuring the thicknesses of a convex and a concave ligaments. From the test results with a local immersion delay, the measurement accuracy within ±50 μm was attained to measure the thicknesses of a convex and a concave ligaments. Nomenclature S1 = First surface echo B1 = First bottom echo B2 = Second bottom echo Vl = Acoustic velocity of longitudinal wave Vs = Acoustic velocity of shear wave