Metallurgical investigation on stainless steel bellows used in satellite launch vehicle

Bellows made of austenitic stainless steel AISI 304 grade are being used as conduit for liquid fuel and oxidizer in propellant tank of satellite launch vehicle. These bellows encountered frequent leakage problems. Leakage locations were found to be along the fusion line of ring to ply weld. In many of such failures, synergistic effect of chloride ions and thermal stresses from welding was the cause identified. Detailed metallurgical characterization of bellows with different weld parameters have been carried out, which served as an efficient tool for qualification of the processing of bellows. This paper highlights various metallurgical features observed in stainless steel bellows during process qualification programme and their impact on the performance.