RESULTS OF EXPERIMENTAL STUDIES AND NUMERICAL MODELING OF INFLUENCE OF WATER-CHEMICAL PARAMETERS UPON INTENSITY OF METAL EROSION-CORROSION IN SINGLE- AND TWO-PHASE FLUID FLOWS AT HPPS AND NPPS

摘要

Operation of NPPs and HPPs is accompanied by implementation of erosive-corrosive effect of fluid upon the metal of working surfaces of equipment and pipelines. Practically all the elements of working circuit made of pearlitic or lean alloy steals and streamlined by one-phase (water) and two-phase (steam-water) flow are subjected to general erosion-corrosion. Due to general erosion-corrosion, carry-over of iron-containing compounds into the working fluid takes place with subsequent formation of deposits in steam generator and other flow channels of power units.Water-chemical regime of NPPs and HPPs is the principal tool for supervision and control of processes of formation of erosion-corrosion iron-containing products and, as a consequence, of their deposition. The most important parameter of water-chemical regime affecting mostly the intensity of general metal erosion-corrosion is the pH value of liquid phase.High intensity of erosion-corrosion process on the working surfaces of steam-water circuit (SWC) and condensate-feed circuit (CFC) being considerable in their space causes its significant input into general carry-over of iron-containing compounds into NPP process circuit. Intensity of erosion-corrosion in steam-water circuit of power units is determined to a great extent by local pH values of liquid film formed and flowing as a dense layer upon the metal surface already at steam humidity degree of more than 1,5-2,0%.With the purpose of solving the practical problems of optimization of NPP and HPP water-chemical regime concerning reduction of erosion-corrosion level intensity in condensate-feeding and steam-water circuits, the methods and software were developed and diagrams were drawn demonstrating relationship of pH_(25) values of one-phase water medium of liquid and steam phases, amine concentration and H_2O humidity degree. Using physical-chemical model of erosion-corrosion RAMEC, data were acquired on capability of various amines to inhibit erosion-corrosion processes in CFC and SWC of NPPs and HPPs.Suggested calculation methods and diagrams of pH values of liquid and steam phases during the change of H_2O aggregate state drawn basing upon them permit determining maximum permissible concentrations of alkalizing amines dispensed into one-phase water medium with appropriate accuracy extent within engineering estimates with provision of required low level of erosion-corrosion intensity and iron-containing compounds in working circuit of power units. The developed software complex RAMEC including possibilities of modeling of water-chemical parameters was used for updating of regulatory branch documents in force in Russia concerning optimization of amount and correction of periodicity of operational control of metal of CFC and SWC elements of NPPs subjected to erosion-corrosion.