METHOD OF CHEMICAL CLEANING OF INTERNAL SURFACE OF HEAT- EXCHANGE EQUIPMENT Russian patent published in 2003 - IPC

FIELD: removal of deposits difficult for solution from internal surface of pipe space of heat- exchange apparatuses producing carbamide. SUBSTANCE: cleaning is carried out with use of mixture of phosphoric and nitric acids with concentration of H₃PO₄ equal to 10-30 per cent by mass, of HNO₃ equal to 15- 25 per cent by mass and corrosion inhibitor in the capacity of flushing solution. Potassium bichromate in the amount of 4.0-6.0 g per liter of flushing solution is utilized as corrosion inhibitor. Deposits are removed at boiling temperature 95-110 C of flushing solution without circulation by way of multiple filling of pipe clearance with subsequent flushing with condensate of water vapor. EFFECT: improved method of cleaning of internal surface of pipe clearance in heat exchange equipment that can be utilized in apparatuses made of any corrosion-resistant materials, titanium included, used in production of carbamide. 1 tbl