Failure Analysis of Stainless Steel Stem Used in Explosive Transfer Assembly (ETA) of High Performance Solid Propulsion System Igniter

Abstract

The adaptor of explosive transfer assembly (ETA) of high performance solid propulsion system igniter used for satellite launch vehicles, which functions as a detonation transfer device, is fabricated from 6.5 mm diameter extruded rod of stainless steels of AISI 304 grade. The stems, as end fittings of ETA were made of 5.5 mm diameter tubes. One of the two stems used in ETA was found ruptured after the high performance solid propulsion system igniter vacuum test. The failed stem was subjected to detailed metallurgical investigations to understand the cause of failure. The observations made were compared with the stem used in the test and did not fail. The failed stem was found to have unacceptable levels of nonmetallic inclusions, while the other stem was practically clean. As the stress experienced at load was beyond the yield point of the material, premature failure occurred by the formation of voids by de-bonding of the inclusions from the matrix. The voids subsequently coalesced to cause fracture. This paper highlights the details of the investigation that was carried out on the fractured stem and established the deleterious effect of inclusions in steel.