Stress corrosion failure of ammonia synthesis waste heat boiler

Abstract

Stainless steel tubes in the waste heat boiler of a 900 t d⁻¹ capacity ammonia plant failed after about 20 months’ operation. Investigations revealed that the tubes, made of Sanicro 30, had suffered stress corrosion cracking as a result of the combined action of stress and a corrosive environment containing chloride ions in an alkaline solution. Crevices present between the tubes and the tube plate provided areas for the build-up of high local concentrations of the corrosive agents. These agents had entered the system with return condensate from the plant, which was passed untreated to the deaerator, and/or as a result of slippage from demineralization units.