THE CHEMICAL-PARAMETERS INFLUENCE UPON TH E CREVICE CORROSION OF THE TUBE-TUBULAR SHEET STEAM-GENERATOR

Corrosion is the major problem affecting the reliability Of steam gene rators. Many corrosion problems can be attributed to local concentrati on effects of aggressive solutes and/or impurities in restricted regio ns, such as tube-tubesheet crevices. The concentration effect, in thes e restricted areas, is of great importance and interest in the design and operation of steam generators. in this study there are presented t he results of corrosion testing performed in secondary circuit specifi c conditions of Nuclear Power Plant operation (temperature 260 degrees C, pressure 5.1. MPa), on crevice simulated devices manufactured from carbon steel (SA 508 class 2) and Incolloy-800. The following testing environments were utilized: demineralized water (pH=9.5 all volatile treatment) condenser raw cooling, water from the Danube (pH=9.5), NaCl solution 100 g/L (pH=10.5). The examination of the corrosion behaviou r of these materials has been realized by metallography and X-ray diff raction. The results are presented as micrographies which distinguish the appearance of pitting corrosion first on the tubesheet material an d eventually in the of very aggresive environment on the tubes materia l. The purpose of this paper is to develop a good understanding of the mechanism of corrosion and oxide growth on carbon steel in simulated crevice devices.