After 10 to 20 months of service, the carbon steel hoppers on three trucks used to transport bulk ammonium nitrate prills developed extensive cracking in the upper walls. The prills were discharged from the steel hoppers using air superchargers that generated an unloading pressure of approximately 11 kPa (7 psi). Each hopper truck held from 9,100 to 11,800 kg (10 to 13 tons) of prills when fully loaded and handled approximately 90,700 kg (100 tons) per month. The walls of the hoppers were made of 2.7 mm (0.105 in.) thick flat-rolled carbon steel sheet of structural quality, conforming to...