Study On Corrosion Behavior Of Alloy 600 Tubing Materials Used For Steam Generator(SG)

Alloy 600 is a Nickel-based alloy material with perfect anti-corrosion and anti-oxidation properties. So it was widely used as the tubing materials of steam generator (SG) in Nuclear Power Plant (NPP). Because of seriously corrosive operation condition, Alloy 600 had been experiencing kinds of materials attack, such as IGA/SCC (Intergranular Attack、Stress Corrosion Cracking)、PWSCC (Primary Water Intergranular-stress Corrosion), SWSCC(Secondary Water Intergranular-stress Corrosion) and wastage. It was reported that more than 70% reactor shutdown accidents were related to rupture of heat transfer tubes of steam generator (SG), which seriously affected the security, reliability, economy of Nuclear Power Plant (NPP). It is very important and necessary to decrease and prevent cracking of heat transfer tubes for reliable, prolonging operation of SG.In this thesis, the corrrosion behaviors of Alloy 600 tubing materials used for steam generator(SG) was studied with electrochemistry methods in different solutions and conditions, e.g. NaOH, Na2SO4, Na2S2O3, Na3PO4, NaCl, and different pH condition. Tafel polarization, AC impedance were employed in this research. Experiment results showed that Alloy 600 became more corrosion sensitive as pH increased from pH 7 to pH 14; small amount electrolyte can accelerate the corrosion of Alloy 600, which ranking as NaOH, Na3PO4, NaCl, Na2SO4, Na2S2O3.High temperature corrosion behaviors of Alloy 600 in different solutions were studied in autoclave, and results showed that the surface of Alloy 600 was covered by the oxides; and corrosion pitting was found in conditions of sodium chloride solution and sodium sulfate solution, and IGA was also found in the condition of sodium chloride solution. The components of solutions was investigated by Atomic Absorption Spectrophotometer, which indicated that Alloy 600 suffered from de chromium corrosion and de of iron corrosion.