Ammonium nitrate induced cracking of a dryer

After less than 1 year of service, extensive cracking of two ammonium nitrate prill dryers was found. The cracking was found to be ammonium nitrate-induced stress corrosion cracking and the failure was attributed to a lack of post-weld stress relieving of the fabricated structures. It was considered likely that the SCC would occur more slowly once the cracks had progressed beyond the region of high residual stresses and that the design operating stresses in the dryer would be insufficient to cause rapid cracking in the dryers. It order to manage the dryers until new ones could be fabricated, the dryers were operated normally with regular inspections to monitor crack growth and to date, no significant addition crack growth of major cracks was observed.

► An ammonium nitrate (AN) dryer cracked due to AN induced stress corrosion cracking.
► The failure was attributed a failure to stress relieve the welded structure.
► The dryer was considered safe to operate until a replacement could be made.