CORROSION INHIBITION IN AN INDUSTRIAL CRYSTALLIZATION PLANT - OPTIMIZING THE PROCESS WITH A STATISTICAL-METHOD

An experimental statistical plan is utilized to solve corrosion proble ms of a section of an industrial plant for the production of caprolact am, consisting of a multistage flash evaporator entirely constructed i n AISI 316L (X2CrNiMo 17 12 2). Preliminary tests show that the nitrat es or acidity due to the sulfuric acid do not influence the corrosive phenomena and confirmed the positive, though costly, effect of adding hydroxylamine sulfate (SI) in the evaporator feed. An experimental pla n was prepared to diminish the cost and dosage of SI in the system: th e experimental statistical approach has allowed us to minimize the num ber of tests required in order to define the system rapidly and adequa tely, and to optimize the required amount of SI. The data processed ha ve been obtained in a two-step experimental plan that allowed us to es tablish a relationship between the logarithm of critical corrosion cur rent (i(cr)) and the concentrations of some evaporator feeding compone nts. In addition, it has been possible to clarify certain corrosion ef fects and to reduce the SI addition up to 1.4 g/l, thereby optimizing the chemical system and considerably reducing maintenance costs. A pla usible explanation of the related effects of some of the feeding compo nents is also proposed.