Dry-coupled pulse echo ultrasonic inspection methodology for solid graphite products of rocket boosters

High modulus solid graphite products are used in nozzle throats of solid rocket boosters. Functionally, nozzle throats are critical and hence require to be inspected thoroughly, Ultrasonic method can be utilised for detecting tight defects/cracks and estimating material properties, such as elastic modulus, grain size, uniformity of structure, etc. For ultrasonic energy to pass to the material, a liquid coupling medium is used conventionally, and hence, commercially available transducers are meant for usage with a liquid couplant. Such a liquid couplant is harmful to graphite products and hence cannot be used. Replaceable solid couplant transducer faces have been developed that can be used on conventional probes for inspection of any product. Studies were conducted to understand various aspects of ultrasonic inspection for critical applications. This paper details the experimentation conducted and analysis done on signals collected for evolving an application methodology and a procedure.