Burst pressure estimation of reworked nozzle weld on spherical domes

Abstract

Propellant tanks of rockets or launch vehicles have nozzles welded to their domes as interfaces for valves or pressurisation/vent lines. These nozzle welds are critical since more often the failure happens here when the tank is pressurised. The considerable difference between the yield and ultimate strength of weld as compared to the parent material is the reason for the low burst pressure of the nozzle welds. To eliminate unacceptable weld defects like porosities, cracks etc., the defective portions are rewelded and are called weld reworks. Residual stress present because of rework, further reduces the burst pressure. In this study, burst pressure estimation of a typical nozzle welded to the dome is analysed by finite element method. The effect of geometric non-linearity of the structure in the prediction of burst pressure is clearly brought out. Also, the burst pressure reduction when weld reworks are carried out in a portion of the weld length and reduction in burst pressure when this rework length increases is demonstrated using finite element analysis.