Computed Tomography - A Diagnostic Tool

Pyrogen Igniter (PI) is a mission critical component used for igniting large rocket motors. PI is made up of propellant grain cast into a Synthetic Resin Bonded Paper (SRBP) tube, which in turn bonded inside Glass Epoxy (GE) casing. The variations in processing of PI may result in non-uniformity in thickness of its constituents and defects at interfaces that can affect performance of PI. X-ray Radiography is widely used to assess the quality of PI during different stages of manufacturing though Radiography compresses 3D volume information of PI into a 2D image. UT is less used because of couplant seepage and difficulty in interpreting the multiple reflection & refraction from different interfaces. This paper discusses the application of Computed Tomography (CT) in diagnosing the indications observed in RT of PI. Radiographs have shown a thickness variation between SRBP and Propellant grain but the boundaries could not be delineated due to the overlapping of the features. Then CT was employed to resolve the ambiguity in identifying the boundaries. CT could reveal all the interfaces, their boundaries including thickness variation noticeably without any overlap. Further investigation has concluded that the thickness variations were due to the mandrel shift during propellant casting.