The sky is falling: chemical characterization and corrosion evaluation of deposition produced during the static testing of solid rocket motors.

Static tests of horizontally restrained rocket motors at the ATK facility in Promontory UT, USA result in the deposition of entrained soil and fuel combustion products, referred to as Test Fire Soil (TFS), over areas as large as 30-50 mile (80-130 km) and at distances up to 10-12 miles (16-20 km) from the test site. Chloride is the main combustion product generated from the ammonium perchlorate-aluminum based composite propellant. Deposition sampling/characterization and a 6-month field corrosivity study using mild steel coupons were conducted in conjunction with the February 25th 2010 FSM-17 static test. The TFS deposition rates at the three study sites ranged from 1 to 5 g/min/m. TFS contained significantly more chloride than the surface soil collected from the test site. The TFS collected during two subsequent tests had similarly elevated chloride, suggesting that the results obtained in this study are applicable to other tests assuming that the rocket fuel composition remains similar. The field-deployed coupons exposed to the TFS had higher corrosion rates (3.6-5.0 mpy) than paired non-exposed coupons (1.6-1.8 mpy). Corrosion rates for all coupons decreased over time, but coupons exposed to the TFS always had a higher rate than the non-exposed. Differences in corrosion rates between the three study sites were also observed, with sites receiving more TFS deposition having higher corrosion rates.