Corrosion of Ti-6Al-4V alloy and 304L stainless steel in liquid nitrogen oxides

Abstract

Liquid dinitrogen tetroxide is normally stored in stainless steel tanks, whereas the mixed oxides of nitrogen, dinitrogen tetroxide plus nitric oxide, may also be stored in titanium alloy vessels. This article presents new data on the corrosion of unstressed 304L stainless steel and Ti-6Al-4V by these rocket propellant oxidizers at 30°C as a function of time at a surface-to-volume ratio of 6 cm1. The results show that dry dinitrogen tetroxide (0.003 and 0.02-wt% water equivalent) is the more corrosive medium towards both alloys: the iron oxidation product dissolves more in dinitrogen tetroxide plus 3% nitric oxide, whereas the titanium alloy corrosion products are more soluble in the NO-free medium. However, attack is extremely limited in both oxidizers. It is finished after 550 days (and probably in less than 55 days) in dinitrogen tetroxide and corresponds to the oxidation of a 30- to 40-A layer of alloy. In dinitrogen tetroxide plus 3% nitric oxide only a fifth of the corrosion takes place, and then within a period of less than 50 days. The results depend substantially on the analysis of the key component metals (Al, Ti, V, Mn, Fe, Cr, and Ni) as determined by state-of-the-art spectrometric methods.