Corrosion of the tube-tubesheet joint in the Candu steam generator at operation resuming after the chemical cleaning of depositions occurred due to the contamination of condense by the cooling water

The purpose of this paper is to establish the corrosion behaviour of the Iy-800 (material of the tube) and SA 508 cl.2 (material of the tube sheet) after the chemical cleaning of the steam generator on the secondary circuit specific components. On the surface of these materials there are initial deposits consisting of oxides and corrosion products. The chemical cleaning was made at temperatures between 60-80oC. The substances included in the chemical cleaning solution are citric acid, Na2EDTA, HEDTA, ammonium citrate, hydrazine hydrate and thiourea. After the chemical cleaning the samples were passivated and corrosion-tested at the typical parameters of the steam generator secondary circuit (demineralized water, pH=9.5, all volatile treatment, temperature 265oC and pressure 5.1 MPa). The results of metallographic and X-ray diffraction examinations are presented as well as the reasons for selecting the best solution for the chemical cleaning. (author)