CORROSION AT THE TUBE TUBE PLATE JOINT IN THE STEAM-GENERATOR IN THE PRESENCE OF DEPOSITS

Corrosion is the major problem affecting the reliability of the steam generator. Many corrosion problems can be attributed to local concentr ation effects of aggresive solutes and/or impurities in restricted reg ions, such as tube-tubesheet crevices. The concentration effect in the se restricted areas is of great importance and present interest in the design and operation of steam generators. In this study there are pre sented the results of corrosion testing performed in the secondary cir cuit specific conditions of Nuclear Power Plant; operation (temperatur e 260 degrees C, pressure 5.1 MPa) on crevice simulated devices manufa ctured from carbon steel (SA 508 class 2) and Incolloy-800. The follow ing testing environments were utilized:NaCl solution 2.5 g/L' (pH=10.5 ); NaCl solution 5.0 g/L @H=10.5); NaCl solution 7.5 g/L (pH = 10.5); Na2SO4 solution l.0 g/L + NaCl solution 7.5 g/L (pH=10.5). The examina tion of corrosion behaviour of these materials has been done by metall ography. The results are presented as micrographyes wich distinguis th e ocurrence of pitting corrosion first on the tubesheet material and e ventually in the presence of very aggressive environment on the tubes material. The purpose of this paper is to developed a good understandi ng of corrosion behaviour of SA 508 and Iy-800 in the presence of depo sits.